diff --git a/frontend/css/styles.css b/frontend/css/styles.css
new file mode 100644
index 0000000..c120c56
--- /dev/null
+++ b/frontend/css/styles.css
@@ -0,0 +1,476 @@
+/* Reset and Base Styles */
+* {
+    margin: 0;
+    padding: 0;
+    box-sizing: border-box;
+}
+
+:root {
+    --primary-color: #4f46e5;
+    --primary-dark: #4338ca;
+    --secondary-color: #6b7280;
+    --success-color: #10b981;
+    --danger-color: #ef4444;
+    --background-color: #f3f4f6;
+    --card-background: #ffffff;
+    --text-color: #1f2937;
+    --text-secondary: #6b7280;
+    --border-color: #e5e7eb;
+    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
+    --radius: 12px;
+    --radius-sm: 8px;
+    --nav-height: 64px;
+    --header-height: 56px;
+}
+
+body {
+    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
+    background-color: var(--background-color);
+    color: var(--text-color);
+    line-height: 1.5;
+    min-height: 100vh;
+    -webkit-font-smoothing: antialiased;
+}
+
+#app {
+    display: flex;
+    flex-direction: column;
+    min-height: 100vh;
+}
+
+/* Header */
+.header {
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    height: var(--header-height);
+    background: var(--card-background);
+    border-bottom: 1px solid var(--border-color);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 100;
+    padding: 0 16px;
+}
+
+.header-title {
+    font-size: 18px;
+    font-weight: 600;
+}
+
+/* Main Content */
+.main-content {
+    flex: 1;
+    padding: calc(var(--header-height) + 16px) 16px calc(var(--nav-height) + 16px);
+    max-width: 600px;
+    margin: 0 auto;
+    width: 100%;
+}
+
+/* Views */
+.view {
+    display: none;
+}
+
+.view.active {
+    display: block;
+}
+
+.view-header {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    margin-bottom: 16px;
+}
+
+.view-header h2 {
+    font-size: 24px;
+    font-weight: 600;
+}
+
+/* Sections */
+.section {
+    margin-top: 24px;
+}
+
+.section h3 {
+    font-size: 16px;
+    font-weight: 600;
+    color: var(--text-secondary);
+    margin-bottom: 12px;
+}
+
+.section h4 {
+    font-size: 14px;
+    font-weight: 600;
+    margin-bottom: 8px;
+}
+
+/* Buttons */
+.btn {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 10px 20px;
+    border: none;
+    border-radius: var(--radius-sm);
+    font-size: 14px;
+    font-weight: 500;
+    cursor: pointer;
+    transition: all 0.2s;
+}
+
+.btn-primary {
+    background: var(--primary-color);
+    color: white;
+}
+
+.btn-primary:hover {
+    background: var(--primary-dark);
+}
+
+.btn-secondary {
+    background: var(--border-color);
+    color: var(--text-color);
+}
+
+.btn-secondary:hover {
+    background: #d1d5db;
+}
+
+.btn-text {
+    background: transparent;
+    color: var(--primary-color);
+    padding: 8px 12px;
+}
+
+.btn-danger {
+    background: var(--danger-color);
+    color: white;
+}
+
+.btn-large {
+    width: 100%;
+    padding: 14px 24px;
+    font-size: 16px;
+}
+
+.btn-small {
+    padding: 6px 12px;
+    font-size: 12px;
+}
+
+/* Quick Actions */
+.quick-actions {
+    margin-bottom: 24px;
+}
+
+/* Cards */
+.card-list {
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+}
+
+.card {
+    background: var(--card-background);
+    border-radius: var(--radius);
+    padding: 16px;
+    box-shadow: var(--shadow);
+}
+
+.card-header {
+    display: flex;
+    justify-content: space-between;
+    align-items: flex-start;
+    margin-bottom: 8px;
+}
+
+.card-title {
+    font-size: 16px;
+    font-weight: 600;
+}
+
+.card-subtitle {
+    font-size: 13px;
+    color: var(--text-secondary);
+}
+
+.card-body {
+    margin-top: 8px;
+}
+
+.card-actions {
+    display: flex;
+    gap: 8px;
+    margin-top: 12px;
+}
+
+.badge {
+    display: inline-block;
+    padding: 2px 8px;
+    border-radius: 12px;
+    font-size: 11px;
+    font-weight: 500;
+    text-transform: uppercase;
+}
+
+.badge-strength {
+    background: #dbeafe;
+    color: #1e40af;
+}
+
+.badge-cardio {
+    background: #fef3c7;
+    color: #92400e;
+}
+
+/* Empty State */
+.empty-state {
+    text-align: center;
+    color: var(--text-secondary);
+    padding: 32px 16px;
+}
+
+/* Forms */
+.form {
+    display: flex;
+    flex-direction: column;
+    gap: 16px;
+}
+
+.form-group {
+    display: flex;
+    flex-direction: column;
+    gap: 6px;
+}
+
+.form-group label {
+    font-size: 14px;
+    font-weight: 500;
+    color: var(--text-secondary);
+}
+
+.form-group input,
+.form-group select,
+.form-group textarea {
+    padding: 12px;
+    border: 1px solid var(--border-color);
+    border-radius: var(--radius-sm);
+    font-size: 16px;
+    background: var(--card-background);
+    color: var(--text-color);
+}
+
+.form-group input:focus,
+.form-group select:focus,
+.form-group textarea:focus {
+    outline: none;
+    border-color: var(--primary-color);
+    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
+}
+
+.form-row {
+    display: grid;
+    grid-template-columns: repeat(3, 1fr);
+    gap: 12px;
+}
+
+/* Tabs */
+.tabs {
+    display: flex;
+    gap: 8px;
+    margin-bottom: 16px;
+    overflow-x: auto;
+    padding-bottom: 4px;
+}
+
+.tab {
+    padding: 8px 16px;
+    border: none;
+    background: var(--border-color);
+    border-radius: 20px;
+    font-size: 14px;
+    font-weight: 500;
+    color: var(--text-secondary);
+    cursor: pointer;
+    white-space: nowrap;
+    transition: all 0.2s;
+}
+
+.tab.active {
+    background: var(--primary-color);
+    color: white;
+}
+
+/* Modal */
+.modal {
+    position: fixed;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: rgba(0, 0, 0, 0.5);
+    display: flex;
+    align-items: flex-end;
+    justify-content: center;
+    z-index: 200;
+}
+
+.modal.hidden {
+    display: none;
+}
+
+.modal-content {
+    background: var(--card-background);
+    border-radius: var(--radius) var(--radius) 0 0;
+    padding: 20px;
+    width: 100%;
+    max-width: 600px;
+    max-height: 90vh;
+    overflow-y: auto;
+}
+
+.modal-header {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    margin-bottom: 20px;
+}
+
+.modal-header h3 {
+    font-size: 18px;
+    font-weight: 600;
+}
+
+/* Bottom Navigation */
+.bottom-nav {
+    position: fixed;
+    bottom: 0;
+    left: 0;
+    right: 0;
+    height: var(--nav-height);
+    background: var(--card-background);
+    border-top: 1px solid var(--border-color);
+    display: flex;
+    justify-content: space-around;
+    align-items: center;
+    padding-bottom: env(safe-area-inset-bottom);
+}
+
+.nav-item {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 4px;
+    padding: 8px 16px;
+    background: none;
+    border: none;
+    color: var(--text-secondary);
+    cursor: pointer;
+    transition: color 0.2s;
+}
+
+.nav-item.active {
+    color: var(--primary-color);
+}
+
+.nav-icon {
+    font-size: 20px;
+}
+
+.nav-label {
+    font-size: 11px;
+    font-weight: 500;
+}
+
+/* Plan Exercise Item */
+.plan-exercise-item {
+    display: flex;
+    gap: 8px;
+    align-items: flex-start;
+    padding: 12px;
+    background: var(--background-color);
+    border-radius: var(--radius-sm);
+    margin-bottom: 8px;
+}
+
+.plan-exercise-item select {
+    flex: 1;
+}
+
+.plan-exercise-item input {
+    width: 70px;
+}
+
+.plan-exercise-item .btn {
+    padding: 8px;
+}
+
+/* Session Entry */
+.session-entry {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    padding: 12px;
+    background: var(--background-color);
+    border-radius: var(--radius-sm);
+}
+
+.entry-info {
+    flex: 1;
+}
+
+.entry-name {
+    font-weight: 500;
+}
+
+.entry-details {
+    font-size: 13px;
+    color: var(--text-secondary);
+}
+
+/* Utilities */
+.hidden {
+    display: none !important;
+}
+
+.text-center {
+    text-align: center;
+}
+
+.mt-2 {
+    margin-top: 8px;
+}
+
+.mt-4 {
+    margin-top: 16px;
+}
+
+/* Responsive adjustments for larger screens */
+@media (min-width: 640px) {
+    .modal-content {
+        border-radius: var(--radius);
+        margin-bottom: 20px;
+    }
+
+    .modal {
+        align-items: center;
+    }
+}
+
+@media (min-width: 768px) {
+    :root {
+        --header-height: 64px;
+    }
+
+    .header-title {
+        font-size: 20px;
+    }
+
+    .main-content {
+        padding: calc(var(--header-height) + 24px) 24px calc(var(--nav-height) + 24px);
+    }
+}
diff --git a/frontend/index.html b/frontend/index.html
new file mode 100644
index 0000000..c43edb9
--- /dev/null
+++ b/frontend/index.html
@@ -0,0 +1,259 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Training Tracker</title>
+    <link rel="stylesheet" href="css/styles.css">
+</head>
+<body>
+    <div id="app">
+        <!-- Header -->
+        <header class="header">
+            <h1 class="header-title">Training Tracker</h1>
+        </header>
+
+        <!-- Main Content -->
+        <main class="main-content">
+            <!-- Dashboard View -->
+            <section id="view-dashboard" class="view active">
+                <h2>Dashboard</h2>
+                <div class="quick-actions">
+                    <button class="btn btn-primary btn-large" onclick="app.startNewSession()">
+                        Start New Session
+                    </button>
+                </div>
+                <div class="section">
+                    <h3>Recent Sessions</h3>
+                    <div id="recent-sessions" class="card-list">
+                        <p class="empty-state">No sessions yet</p>
+                    </div>
+                </div>
+            </section>
+
+            <!-- Sessions View -->
+            <section id="view-sessions" class="view">
+                <div class="view-header">
+                    <h2>Sessions</h2>
+                    <button class="btn btn-primary" onclick="app.startNewSession()">New</button>
+                </div>
+                <div id="sessions-list" class="card-list">
+                    <p class="empty-state">No sessions yet</p>
+                </div>
+            </section>
+
+            <!-- Session Detail View -->
+            <section id="view-session-detail" class="view">
+                <div class="view-header">
+                    <button class="btn btn-text" onclick="app.navigateTo('sessions')">Back</button>
+                    <h2 id="session-detail-title">Session</h2>
+                </div>
+                <div id="session-detail-content"></div>
+            </section>
+
+            <!-- Log Session View -->
+            <section id="view-log-session" class="view">
+                <div class="view-header">
+                    <button class="btn btn-text" onclick="app.navigateTo('sessions')">Cancel</button>
+                    <h2>Log Session</h2>
+                </div>
+                <form id="session-form" class="form">
+                    <div class="form-group">
+                        <label for="session-date">Date</label>
+                        <input type="datetime-local" id="session-date" required>
+                    </div>
+                    <div class="form-group">
+                        <label for="session-plan">Training Plan (Optional)</label>
+                        <select id="session-plan">
+                            <option value="">No plan</option>
+                        </select>
+                    </div>
+                    <div class="form-group">
+                        <label for="session-notes">Notes</label>
+                        <textarea id="session-notes" rows="3" placeholder="How did it go?"></textarea>
+                    </div>
+                    <button type="submit" class="btn btn-primary btn-large">Create Session</button>
+                </form>
+
+                <div id="session-entries-section" class="section hidden">
+                    <h3>Exercises</h3>
+                    <div id="session-entries" class="card-list"></div>
+                    <button class="btn btn-secondary" onclick="app.showAddEntryForm()">Add Exercise</button>
+                </div>
+            </section>
+
+            <!-- Add Entry Modal -->
+            <div id="add-entry-modal" class="modal hidden">
+                <div class="modal-content">
+                    <div class="modal-header">
+                        <h3>Add Exercise Entry</h3>
+                        <button class="btn btn-text" onclick="app.hideAddEntryForm()">Cancel</button>
+                    </div>
+                    <form id="entry-form" class="form">
+                        <div class="form-group">
+                            <label for="entry-exercise">Exercise</label>
+                            <select id="entry-exercise" required></select>
+                        </div>
+                        <div id="strength-fields">
+                            <div class="form-row">
+                                <div class="form-group">
+                                    <label for="entry-weight">Weight (kg)</label>
+                                    <input type="number" id="entry-weight" step="0.5" min="0">
+                                </div>
+                                <div class="form-group">
+                                    <label for="entry-sets">Sets</label>
+                                    <input type="number" id="entry-sets" min="0">
+                                </div>
+                                <div class="form-group">
+                                    <label for="entry-reps">Reps</label>
+                                    <input type="number" id="entry-reps" min="0">
+                                </div>
+                            </div>
+                        </div>
+                        <div id="cardio-fields" class="hidden">
+                            <div class="form-row">
+                                <div class="form-group">
+                                    <label for="entry-duration">Duration (min)</label>
+                                    <input type="number" id="entry-duration" min="0">
+                                </div>
+                                <div class="form-group">
+                                    <label for="entry-distance">Distance (km)</label>
+                                    <input type="number" id="entry-distance" step="0.1" min="0">
+                                </div>
+                            </div>
+                            <div class="form-group">
+                                <label for="entry-hr">Avg Heart Rate</label>
+                                <input type="number" id="entry-hr" min="0">
+                            </div>
+                        </div>
+                        <div class="form-group">
+                            <label for="entry-notes">Notes</label>
+                            <input type="text" id="entry-notes" placeholder="Optional notes">
+                        </div>
+                        <button type="submit" class="btn btn-primary btn-large">Add Entry</button>
+                    </form>
+                </div>
+            </div>
+
+            <!-- Exercises View -->
+            <section id="view-exercises" class="view">
+                <div class="view-header">
+                    <h2>Exercises</h2>
+                    <button class="btn btn-primary" onclick="app.showExerciseForm()">Add</button>
+                </div>
+                <div class="tabs">
+                    <button class="tab active" data-filter="all">All</button>
+                    <button class="tab" data-filter="strength">Strength</button>
+                    <button class="tab" data-filter="cardio">Cardio</button>
+                </div>
+                <div id="exercises-list" class="card-list">
+                    <p class="empty-state">No exercises yet</p>
+                </div>
+            </section>
+
+            <!-- Exercise Form Modal -->
+            <div id="exercise-modal" class="modal hidden">
+                <div class="modal-content">
+                    <div class="modal-header">
+                        <h3 id="exercise-modal-title">Add Exercise</h3>
+                        <button class="btn btn-text" onclick="app.hideExerciseForm()">Cancel</button>
+                    </div>
+                    <form id="exercise-form" class="form">
+                        <input type="hidden" id="exercise-id">
+                        <div class="form-group">
+                            <label for="exercise-name">Name</label>
+                            <input type="text" id="exercise-name" required placeholder="e.g., Bench Press">
+                        </div>
+                        <div class="form-group">
+                            <label for="exercise-type">Type</label>
+                            <select id="exercise-type" required>
+                                <option value="strength">Strength</option>
+                                <option value="cardio">Cardio</option>
+                            </select>
+                        </div>
+                        <div class="form-group">
+                            <label for="exercise-muscle">Muscle Group</label>
+                            <input type="text" id="exercise-muscle" placeholder="e.g., Chest">
+                        </div>
+                        <div class="form-group">
+                            <label for="exercise-description">Description</label>
+                            <textarea id="exercise-description" rows="2" placeholder="Optional description"></textarea>
+                        </div>
+                        <button type="submit" class="btn btn-primary btn-large">Save Exercise</button>
+                    </form>
+                </div>
+            </div>
+
+            <!-- Plans View -->
+            <section id="view-plans" class="view">
+                <div class="view-header">
+                    <h2>Training Plans</h2>
+                    <button class="btn btn-primary" onclick="app.showPlanForm()">Add</button>
+                </div>
+                <div id="plans-list" class="card-list">
+                    <p class="empty-state">No plans yet</p>
+                </div>
+            </section>
+
+            <!-- Plan Form Modal -->
+            <div id="plan-modal" class="modal hidden">
+                <div class="modal-content">
+                    <div class="modal-header">
+                        <h3 id="plan-modal-title">Add Training Plan</h3>
+                        <button class="btn btn-text" onclick="app.hidePlanForm()">Cancel</button>
+                    </div>
+                    <form id="plan-form" class="form">
+                        <input type="hidden" id="plan-id">
+                        <div class="form-group">
+                            <label for="plan-name">Name</label>
+                            <input type="text" id="plan-name" required placeholder="e.g., Push Day">
+                        </div>
+                        <div class="form-group">
+                            <label for="plan-description">Description</label>
+                            <textarea id="plan-description" rows="2" placeholder="Optional description"></textarea>
+                        </div>
+                        <div class="section">
+                            <h4>Exercises</h4>
+                            <div id="plan-exercises-list"></div>
+                            <button type="button" class="btn btn-secondary" onclick="app.addPlanExercise()">Add Exercise</button>
+                        </div>
+                        <button type="submit" class="btn btn-primary btn-large">Save Plan</button>
+                    </form>
+                </div>
+            </div>
+
+            <!-- Plan Detail View -->
+            <section id="view-plan-detail" class="view">
+                <div class="view-header">
+                    <button class="btn btn-text" onclick="app.navigateTo('plans')">Back</button>
+                    <h2 id="plan-detail-title">Plan</h2>
+                </div>
+                <div id="plan-detail-content"></div>
+            </section>
+        </main>
+
+        <!-- Bottom Navigation -->
+        <nav class="bottom-nav">
+            <button class="nav-item active" data-view="dashboard">
+                <span class="nav-icon">&#127968;</span>
+                <span class="nav-label">Home</span>
+            </button>
+            <button class="nav-item" data-view="sessions">
+                <span class="nav-icon">&#128221;</span>
+                <span class="nav-label">Sessions</span>
+            </button>
+            <button class="nav-item" data-view="exercises">
+                <span class="nav-icon">&#128170;</span>
+                <span class="nav-label">Exercises</span>
+            </button>
+            <button class="nav-item" data-view="plans">
+                <span class="nav-icon">&#128203;</span>
+                <span class="nav-label">Plans</span>
+            </button>
+        </nav>
+    </div>
+
+    <script src="js/api.js"></script>
+    <script src="js/app.js"></script>
+</body>
+</html>
diff --git a/frontend/js/api.js b/frontend/js/api.js
new file mode 100644
index 0000000..a067d79
--- /dev/null
+++ b/frontend/js/api.js
@@ -0,0 +1,139 @@
+// API Client for Training Tracker
+
+const API_BASE_URL = 'http://localhost:8080/api';
+
+class ApiClient {
+    constructor(baseUrl = API_BASE_URL) {
+        this.baseUrl = baseUrl;
+    }
+
+    async request(endpoint, options = {}) {
+        const url = `${this.baseUrl}${endpoint}`;
+        const config = {
+            headers: {
+                'Content-Type': 'application/json',
+                ...options.headers,
+            },
+            ...options,
+        };
+
+        if (config.body && typeof config.body === 'object') {
+            config.body = JSON.stringify(config.body);
+        }
+
+        try {
+            const response = await fetch(url, config);
+
+            if (response.status === 204) {
+                return null;
+            }
+
+            const data = await response.json();
+
+            if (!response.ok) {
+                throw new Error(data.error || 'API request failed');
+            }
+
+            return data;
+        } catch (error) {
+            console.error('API Error:', error);
+            throw error;
+        }
+    }
+
+    // Exercises
+    async getExercises() {
+        return this.request('/exercises');
+    }
+
+    async getExercise(id) {
+        return this.request(`/exercises/${id}`);
+    }
+
+    async createExercise(data) {
+        return this.request('/exercises', {
+            method: 'POST',
+            body: data,
+        });
+    }
+
+    async updateExercise(id, data) {
+        return this.request(`/exercises/${id}`, {
+            method: 'PUT',
+            body: data,
+        });
+    }
+
+    async deleteExercise(id) {
+        return this.request(`/exercises/${id}`, {
+            method: 'DELETE',
+        });
+    }
+
+    // Training Plans
+    async getPlans() {
+        return this.request('/plans');
+    }
+
+    async getPlan(id) {
+        return this.request(`/plans/${id}`);
+    }
+
+    async createPlan(data) {
+        return this.request('/plans', {
+            method: 'POST',
+            body: data,
+        });
+    }
+
+    async updatePlan(id, data) {
+        return this.request(`/plans/${id}`, {
+            method: 'PUT',
+            body: data,
+        });
+    }
+
+    async deletePlan(id) {
+        return this.request(`/plans/${id}`, {
+            method: 'DELETE',
+        });
+    }
+
+    // Sessions
+    async getSessions() {
+        return this.request('/sessions');
+    }
+
+    async getSession(id) {
+        return this.request(`/sessions/${id}`);
+    }
+
+    async createSession(data) {
+        return this.request('/sessions', {
+            method: 'POST',
+            body: data,
+        });
+    }
+
+    async updateSession(id, data) {
+        return this.request(`/sessions/${id}`, {
+            method: 'PUT',
+            body: data,
+        });
+    }
+
+    async deleteSession(id) {
+        return this.request(`/sessions/${id}`, {
+            method: 'DELETE',
+        });
+    }
+
+    async addSessionEntry(sessionId, data) {
+        return this.request(`/sessions/${sessionId}/entries`, {
+            method: 'POST',
+            body: data,
+        });
+    }
+}
+
+const api = new ApiClient();
diff --git a/frontend/js/app.js b/frontend/js/app.js
new file mode 100644
index 0000000..0931aa6
--- /dev/null
+++ b/frontend/js/app.js
@@ -0,0 +1,718 @@
+// Training Tracker App
+
+const app = {
+    currentView: 'dashboard',
+    exercises: [],
+    plans: [],
+    sessions: [],
+    currentSession: null,
+    currentPlan: null,
+    exerciseFilter: 'all',
+
+    // Initialize the app
+    async init() {
+        this.setupNavigation();
+        this.setupForms();
+        this.setupTabs();
+        await this.loadData();
+        this.render();
+    },
+
+    // Setup navigation
+    setupNavigation() {
+        document.querySelectorAll('.nav-item').forEach(item => {
+            item.addEventListener('click', () => {
+                const view = item.dataset.view;
+                this.navigateTo(view);
+            });
+        });
+    },
+
+    // Navigate to a view
+    navigateTo(viewName) {
+        // Hide all views
+        document.querySelectorAll('.view').forEach(view => {
+            view.classList.remove('active');
+        });
+
+        // Show target view
+        const targetView = document.getElementById(`view-${viewName}`);
+        if (targetView) {
+            targetView.classList.add('active');
+        }
+
+        // Update nav items
+        document.querySelectorAll('.nav-item').forEach(item => {
+            item.classList.toggle('active', item.dataset.view === viewName);
+        });
+
+        this.currentView = viewName;
+        this.render();
+    },
+
+    // Setup form handlers
+    setupForms() {
+        // Exercise form
+        document.getElementById('exercise-form').addEventListener('submit', async (e) => {
+            e.preventDefault();
+            await this.saveExercise();
+        });
+
+        // Plan form
+        document.getElementById('plan-form').addEventListener('submit', async (e) => {
+            e.preventDefault();
+            await this.savePlan();
+        });
+
+        // Session form
+        document.getElementById('session-form').addEventListener('submit', async (e) => {
+            e.preventDefault();
+            await this.saveSession();
+        });
+
+        // Entry form
+        document.getElementById('entry-form').addEventListener('submit', async (e) => {
+            e.preventDefault();
+            await this.saveEntry();
+        });
+
+        // Exercise select change (for entry form)
+        document.getElementById('entry-exercise').addEventListener('change', (e) => {
+            this.updateEntryFields(e.target.value);
+        });
+    },
+
+    // Setup tabs
+    setupTabs() {
+        document.querySelectorAll('.tab').forEach(tab => {
+            tab.addEventListener('click', () => {
+                const filter = tab.dataset.filter;
+                this.exerciseFilter = filter;
+                document.querySelectorAll('.tab').forEach(t => t.classList.remove('active'));
+                tab.classList.add('active');
+                this.renderExercises();
+            });
+        });
+    },
+
+    // Load all data
+    async loadData() {
+        try {
+            [this.exercises, this.plans, this.sessions] = await Promise.all([
+                api.getExercises(),
+                api.getPlans(),
+                api.getSessions(),
+            ]);
+        } catch (error) {
+            console.error('Failed to load data:', error);
+        }
+    },
+
+    // Render current view
+    render() {
+        switch (this.currentView) {
+            case 'dashboard':
+                this.renderDashboard();
+                break;
+            case 'sessions':
+                this.renderSessions();
+                break;
+            case 'exercises':
+                this.renderExercises();
+                break;
+            case 'plans':
+                this.renderPlans();
+                break;
+        }
+    },
+
+    // Render dashboard
+    renderDashboard() {
+        const container = document.getElementById('recent-sessions');
+        const recentSessions = this.sessions.slice(0, 5);
+
+        if (recentSessions.length === 0) {
+            container.innerHTML = '<p class="empty-state">No sessions yet. Start your first workout!</p>';
+            return;
+        }
+
+        container.innerHTML = recentSessions.map(session => this.renderSessionCard(session)).join('');
+    },
+
+    // Render sessions list
+    renderSessions() {
+        const container = document.getElementById('sessions-list');
+
+        if (this.sessions.length === 0) {
+            container.innerHTML = '<p class="empty-state">No sessions yet</p>';
+            return;
+        }
+
+        container.innerHTML = this.sessions.map(session => this.renderSessionCard(session)).join('');
+    },
+
+    // Render session card
+    renderSessionCard(session) {
+        const date = new Date(session.date).toLocaleDateString('en-US', {
+            weekday: 'short',
+            month: 'short',
+            day: 'numeric',
+        });
+        const planName = session.plan ? session.plan.name : 'No plan';
+        const entryCount = session.entries ? session.entries.length : 0;
+
+        return `
+            <div class="card" onclick="app.viewSession(${session.id})">
+                <div class="card-header">
+                    <div>
+                        <div class="card-title">${date}</div>
+                        <div class="card-subtitle">${planName}</div>
+                    </div>
+                    <span class="badge badge-strength">${entryCount} exercises</span>
+                </div>
+                ${session.notes ? `<div class="card-body">${session.notes}</div>` : ''}
+            </div>
+        `;
+    },
+
+    // View session details
+    async viewSession(id) {
+        try {
+            this.currentSession = await api.getSession(id);
+            this.renderSessionDetail();
+            document.querySelectorAll('.view').forEach(v => v.classList.remove('active'));
+            document.getElementById('view-session-detail').classList.add('active');
+        } catch (error) {
+            alert('Failed to load session');
+        }
+    },
+
+    // Render session detail
+    renderSessionDetail() {
+        const session = this.currentSession;
+        if (!session) return;
+
+        const date = new Date(session.date).toLocaleDateString('en-US', {
+            weekday: 'long',
+            year: 'numeric',
+            month: 'long',
+            day: 'numeric',
+        });
+
+        document.getElementById('session-detail-title').textContent = date;
+
+        let html = '';
+        if (session.plan) {
+            html += `<p class="card-subtitle">Plan: ${session.plan.name}</p>`;
+        }
+        if (session.notes) {
+            html += `<p class="mt-2">${session.notes}</p>`;
+        }
+
+        html += '<div class="section"><h3>Exercises</h3><div class="card-list">';
+
+        if (session.entries && session.entries.length > 0) {
+            session.entries.forEach(entry => {
+                const exercise = entry.exercise || {};
+                let details = '';
+
+                if (exercise.type === 'cardio') {
+                    const parts = [];
+                    if (entry.duration) parts.push(`${Math.floor(entry.duration / 60)} min`);
+                    if (entry.distance) parts.push(`${entry.distance} km`);
+                    if (entry.heart_rate) parts.push(`${entry.heart_rate} bpm`);
+                    details = parts.join(' | ');
+                } else {
+                    const parts = [];
+                    if (entry.weight) parts.push(`${entry.weight} kg`);
+                    if (entry.sets_completed) parts.push(`${entry.sets_completed} sets`);
+                    if (entry.reps) parts.push(`${entry.reps} reps`);
+                    details = parts.join(' x ');
+                }
+
+                html += `
+                    <div class="session-entry">
+                        <div class="entry-info">
+                            <div class="entry-name">${exercise.name || 'Exercise'}</div>
+                            <div class="entry-details">${details}</div>
+                            ${entry.notes ? `<div class="entry-details">${entry.notes}</div>` : ''}
+                        </div>
+                        <span class="badge ${exercise.type === 'cardio' ? 'badge-cardio' : 'badge-strength'}">${exercise.type || 'strength'}</span>
+                    </div>
+                `;
+            });
+        } else {
+            html += '<p class="empty-state">No exercises logged</p>';
+        }
+
+        html += '</div></div>';
+
+        html += `
+            <div class="card-actions mt-4">
+                <button class="btn btn-danger" onclick="app.deleteSession(${session.id})">Delete Session</button>
+            </div>
+        `;
+
+        document.getElementById('session-detail-content').innerHTML = html;
+    },
+
+    // Start new session
+    startNewSession() {
+        this.currentSession = null;
+        document.getElementById('session-form').reset();
+        document.getElementById('session-date').value = new Date().toISOString().slice(0, 16);
+        document.getElementById('session-entries-section').classList.add('hidden');
+        document.getElementById('session-entries').innerHTML = '';
+
+        // Populate plans dropdown
+        const planSelect = document.getElementById('session-plan');
+        planSelect.innerHTML = '<option value="">No plan</option>' +
+            this.plans.map(p => `<option value="${p.id}">${p.name}</option>`).join('');
+
+        document.querySelectorAll('.view').forEach(v => v.classList.remove('active'));
+        document.getElementById('view-log-session').classList.add('active');
+    },
+
+    // Save session
+    async saveSession() {
+        const date = document.getElementById('session-date').value;
+        const planId = document.getElementById('session-plan').value;
+        const notes = document.getElementById('session-notes').value;
+
+        const data = {
+            date: new Date(date).toISOString(),
+            notes: notes,
+        };
+        if (planId) {
+            data.plan_id = parseInt(planId);
+        }
+
+        try {
+            if (this.currentSession) {
+                this.currentSession = await api.updateSession(this.currentSession.id, data);
+            } else {
+                this.currentSession = await api.createSession(data);
+            }
+
+            // Show entries section
+            document.getElementById('session-entries-section').classList.remove('hidden');
+            this.renderSessionEntries();
+
+            // Reload sessions
+            this.sessions = await api.getSessions();
+        } catch (error) {
+            alert('Failed to save session');
+        }
+    },
+
+    // Render session entries
+    renderSessionEntries() {
+        const container = document.getElementById('session-entries');
+        const entries = this.currentSession?.entries || [];
+
+        if (entries.length === 0) {
+            container.innerHTML = '<p class="empty-state">No exercises yet. Add your first one!</p>';
+            return;
+        }
+
+        container.innerHTML = entries.map(entry => {
+            const exercise = entry.exercise || {};
+            let details = '';
+
+            if (exercise.type === 'cardio') {
+                const parts = [];
+                if (entry.duration) parts.push(`${Math.floor(entry.duration / 60)} min`);
+                if (entry.distance) parts.push(`${entry.distance} km`);
+                details = parts.join(' | ');
+            } else {
+                const parts = [];
+                if (entry.weight) parts.push(`${entry.weight} kg`);
+                if (entry.sets_completed) parts.push(`${entry.sets_completed} sets`);
+                if (entry.reps) parts.push(`${entry.reps} reps`);
+                details = parts.join(' x ');
+            }
+
+            return `
+                <div class="session-entry">
+                    <div class="entry-info">
+                        <div class="entry-name">${exercise.name || 'Exercise'}</div>
+                        <div class="entry-details">${details}</div>
+                    </div>
+                </div>
+            `;
+        }).join('');
+    },
+
+    // Show add entry form
+    showAddEntryForm() {
+        const select = document.getElementById('entry-exercise');
+        select.innerHTML = '<option value="">Select exercise</option>' +
+            this.exercises.map(e => `<option value="${e.id}" data-type="${e.type}">${e.name}</option>`).join('');
+
+        document.getElementById('entry-form').reset();
+        document.getElementById('strength-fields').classList.remove('hidden');
+        document.getElementById('cardio-fields').classList.add('hidden');
+        document.getElementById('add-entry-modal').classList.remove('hidden');
+    },
+
+    // Hide add entry form
+    hideAddEntryForm() {
+        document.getElementById('add-entry-modal').classList.add('hidden');
+    },
+
+    // Update entry fields based on exercise type
+    updateEntryFields(exerciseId) {
+        const exercise = this.exercises.find(e => e.id === parseInt(exerciseId));
+        const isCardio = exercise && exercise.type === 'cardio';
+
+        document.getElementById('strength-fields').classList.toggle('hidden', isCardio);
+        document.getElementById('cardio-fields').classList.toggle('hidden', !isCardio);
+    },
+
+    // Save entry
+    async saveEntry() {
+        if (!this.currentSession) return;
+
+        const exerciseId = parseInt(document.getElementById('entry-exercise').value);
+        const exercise = this.exercises.find(e => e.id === exerciseId);
+
+        const data = {
+            exercise_id: exerciseId,
+            notes: document.getElementById('entry-notes').value,
+        };
+
+        if (exercise && exercise.type === 'cardio') {
+            const duration = parseInt(document.getElementById('entry-duration').value);
+            if (duration) data.duration = duration * 60; // convert to seconds
+            const distance = parseFloat(document.getElementById('entry-distance').value);
+            if (distance) data.distance = distance;
+            const hr = parseInt(document.getElementById('entry-hr').value);
+            if (hr) data.heart_rate = hr;
+        } else {
+            const weight = parseFloat(document.getElementById('entry-weight').value);
+            if (weight) data.weight = weight;
+            const sets = parseInt(document.getElementById('entry-sets').value);
+            if (sets) data.sets_completed = sets;
+            const reps = parseInt(document.getElementById('entry-reps').value);
+            if (reps) data.reps = reps;
+        }
+
+        try {
+            await api.addSessionEntry(this.currentSession.id, data);
+            this.currentSession = await api.getSession(this.currentSession.id);
+            this.renderSessionEntries();
+            this.hideAddEntryForm();
+        } catch (error) {
+            alert('Failed to add entry');
+        }
+    },
+
+    // Delete session
+    async deleteSession(id) {
+        if (!confirm('Are you sure you want to delete this session?')) return;
+
+        try {
+            await api.deleteSession(id);
+            this.sessions = await api.getSessions();
+            this.navigateTo('sessions');
+        } catch (error) {
+            alert('Failed to delete session');
+        }
+    },
+
+    // Render exercises list
+    renderExercises() {
+        const container = document.getElementById('exercises-list');
+        let filtered = this.exercises;
+
+        if (this.exerciseFilter !== 'all') {
+            filtered = this.exercises.filter(e => e.type === this.exerciseFilter);
+        }
+
+        if (filtered.length === 0) {
+            container.innerHTML = '<p class="empty-state">No exercises yet</p>';
+            return;
+        }
+
+        container.innerHTML = filtered.map(exercise => `
+            <div class="card">
+                <div class="card-header">
+                    <div>
+                        <div class="card-title">${exercise.name}</div>
+                        ${exercise.muscle_group ? `<div class="card-subtitle">${exercise.muscle_group}</div>` : ''}
+                    </div>
+                    <span class="badge ${exercise.type === 'cardio' ? 'badge-cardio' : 'badge-strength'}">${exercise.type}</span>
+                </div>
+                ${exercise.description ? `<div class="card-body">${exercise.description}</div>` : ''}
+                <div class="card-actions">
+                    <button class="btn btn-secondary btn-small" onclick="app.editExercise(${exercise.id})">Edit</button>
+                    <button class="btn btn-danger btn-small" onclick="app.deleteExercise(${exercise.id})">Delete</button>
+                </div>
+            </div>
+        `).join('');
+    },
+
+    // Show exercise form
+    showExerciseForm(exercise = null) {
+        document.getElementById('exercise-modal-title').textContent = exercise ? 'Edit Exercise' : 'Add Exercise';
+        document.getElementById('exercise-id').value = exercise ? exercise.id : '';
+        document.getElementById('exercise-name').value = exercise ? exercise.name : '';
+        document.getElementById('exercise-type').value = exercise ? exercise.type : 'strength';
+        document.getElementById('exercise-muscle').value = exercise ? exercise.muscle_group : '';
+        document.getElementById('exercise-description').value = exercise ? exercise.description : '';
+        document.getElementById('exercise-modal').classList.remove('hidden');
+    },
+
+    // Hide exercise form
+    hideExerciseForm() {
+        document.getElementById('exercise-modal').classList.add('hidden');
+    },
+
+    // Edit exercise
+    async editExercise(id) {
+        const exercise = this.exercises.find(e => e.id === id);
+        if (exercise) {
+            this.showExerciseForm(exercise);
+        }
+    },
+
+    // Save exercise
+    async saveExercise() {
+        const id = document.getElementById('exercise-id').value;
+        const data = {
+            name: document.getElementById('exercise-name').value,
+            type: document.getElementById('exercise-type').value,
+            muscle_group: document.getElementById('exercise-muscle').value,
+            description: document.getElementById('exercise-description').value,
+        };
+
+        try {
+            if (id) {
+                await api.updateExercise(id, data);
+            } else {
+                await api.createExercise(data);
+            }
+            this.exercises = await api.getExercises();
+            this.hideExerciseForm();
+            this.renderExercises();
+        } catch (error) {
+            alert('Failed to save exercise');
+        }
+    },
+
+    // Delete exercise
+    async deleteExercise(id) {
+        if (!confirm('Are you sure you want to delete this exercise?')) return;
+
+        try {
+            await api.deleteExercise(id);
+            this.exercises = await api.getExercises();
+            this.renderExercises();
+        } catch (error) {
+            alert('Failed to delete exercise');
+        }
+    },
+
+    // Render plans list
+    renderPlans() {
+        const container = document.getElementById('plans-list');
+
+        if (this.plans.length === 0) {
+            container.innerHTML = '<p class="empty-state">No training plans yet</p>';
+            return;
+        }
+
+        container.innerHTML = this.plans.map(plan => `
+            <div class="card" onclick="app.viewPlan(${plan.id})">
+                <div class="card-header">
+                    <div>
+                        <div class="card-title">${plan.name}</div>
+                        ${plan.description ? `<div class="card-subtitle">${plan.description}</div>` : ''}
+                    </div>
+                </div>
+                <div class="card-actions">
+                    <button class="btn btn-secondary btn-small" onclick="event.stopPropagation(); app.editPlan(${plan.id})">Edit</button>
+                    <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); app.deletePlan(${plan.id})">Delete</button>
+                </div>
+            </div>
+        `).join('');
+    },
+
+    // View plan detail
+    async viewPlan(id) {
+        try {
+            this.currentPlan = await api.getPlan(id);
+            this.renderPlanDetail();
+            document.querySelectorAll('.view').forEach(v => v.classList.remove('active'));
+            document.getElementById('view-plan-detail').classList.add('active');
+        } catch (error) {
+            alert('Failed to load plan');
+        }
+    },
+
+    // Render plan detail
+    renderPlanDetail() {
+        const plan = this.currentPlan;
+        if (!plan) return;
+
+        document.getElementById('plan-detail-title').textContent = plan.name;
+
+        let html = '';
+        if (plan.description) {
+            html += `<p class="card-subtitle">${plan.description}</p>`;
+        }
+
+        html += '<div class="section"><h3>Exercises</h3><div class="card-list">';
+
+        if (plan.exercises && plan.exercises.length > 0) {
+            plan.exercises.forEach((pe, index) => {
+                const exercise = pe.exercise || {};
+                let details = [];
+                if (pe.sets) details.push(`${pe.sets} sets`);
+                if (pe.reps) details.push(`${pe.reps} reps`);
+                if (pe.duration) details.push(`${Math.floor(pe.duration / 60)} min`);
+
+                html += `
+                    <div class="session-entry">
+                        <div class="entry-info">
+                            <div class="entry-name">${index + 1}. ${exercise.name || 'Exercise'}</div>
+                            <div class="entry-details">${details.join(' x ') || 'No targets set'}</div>
+                        </div>
+                        <span class="badge ${exercise.type === 'cardio' ? 'badge-cardio' : 'badge-strength'}">${exercise.type || 'strength'}</span>
+                    </div>
+                `;
+            });
+        } else {
+            html += '<p class="empty-state">No exercises in this plan</p>';
+        }
+
+        html += '</div></div>';
+
+        html += `
+            <div class="card-actions mt-4">
+                <button class="btn btn-primary" onclick="app.startSessionFromPlan(${plan.id})">Start Session</button>
+            </div>
+        `;
+
+        document.getElementById('plan-detail-content').innerHTML = html;
+    },
+
+    // Start session from plan
+    startSessionFromPlan(planId) {
+        this.startNewSession();
+        document.getElementById('session-plan').value = planId;
+    },
+
+    // Show plan form
+    showPlanForm(plan = null) {
+        document.getElementById('plan-modal-title').textContent = plan ? 'Edit Plan' : 'Add Training Plan';
+        document.getElementById('plan-id').value = plan ? plan.id : '';
+        document.getElementById('plan-name').value = plan ? plan.name : '';
+        document.getElementById('plan-description').value = plan ? plan.description : '';
+
+        const exercisesList = document.getElementById('plan-exercises-list');
+        exercisesList.innerHTML = '';
+
+        if (plan && plan.exercises) {
+            plan.exercises.forEach(pe => this.addPlanExerciseRow(pe));
+        }
+
+        document.getElementById('plan-modal').classList.remove('hidden');
+    },
+
+    // Hide plan form
+    hidePlanForm() {
+        document.getElementById('plan-modal').classList.add('hidden');
+    },
+
+    // Add plan exercise row
+    addPlanExercise() {
+        this.addPlanExerciseRow();
+    },
+
+    addPlanExerciseRow(data = null) {
+        const container = document.getElementById('plan-exercises-list');
+        const index = container.children.length;
+
+        const div = document.createElement('div');
+        div.className = 'plan-exercise-item';
+        div.innerHTML = `
+            <select name="exercise_id" required>
+                <option value="">Select</option>
+                ${this.exercises.map(e => `<option value="${e.id}" ${data && data.exercise_id === e.id ? 'selected' : ''}>${e.name}</option>`).join('')}
+            </select>
+            <input type="number" name="sets" placeholder="Sets" min="0" value="${data?.sets || ''}">
+            <input type="number" name="reps" placeholder="Reps" min="0" value="${data?.reps || ''}">
+            <button type="button" class="btn btn-danger btn-small" onclick="this.parentElement.remove()">X</button>
+        `;
+        container.appendChild(div);
+    },
+
+    // Edit plan
+    async editPlan(id) {
+        try {
+            const plan = await api.getPlan(id);
+            this.showPlanForm(plan);
+        } catch (error) {
+            alert('Failed to load plan');
+        }
+    },
+
+    // Save plan
+    async savePlan() {
+        const id = document.getElementById('plan-id').value;
+        const exercises = [];
+
+        document.querySelectorAll('#plan-exercises-list .plan-exercise-item').forEach((item, index) => {
+            const exerciseId = item.querySelector('[name="exercise_id"]').value;
+            const sets = item.querySelector('[name="sets"]').value;
+            const reps = item.querySelector('[name="reps"]').value;
+
+            if (exerciseId) {
+                exercises.push({
+                    exercise_id: parseInt(exerciseId),
+                    sets: sets ? parseInt(sets) : 0,
+                    reps: reps ? parseInt(reps) : 0,
+                    order: index,
+                });
+            }
+        });
+
+        const data = {
+            name: document.getElementById('plan-name').value,
+            description: document.getElementById('plan-description').value,
+            exercises: exercises,
+        };
+
+        try {
+            if (id) {
+                await api.updatePlan(id, data);
+            } else {
+                await api.createPlan(data);
+            }
+            this.plans = await api.getPlans();
+            this.hidePlanForm();
+            this.renderPlans();
+        } catch (error) {
+            alert('Failed to save plan');
+        }
+    },
+
+    // Delete plan
+    async deletePlan(id) {
+        if (!confirm('Are you sure you want to delete this plan?')) return;
+
+        try {
+            await api.deletePlan(id);
+            this.plans = await api.getPlans();
+            this.renderPlans();
+        } catch (error) {
+            alert('Failed to delete plan');
+        }
+    },
+};
+
+// Initialize app when DOM is ready
+document.addEventListener('DOMContentLoaded', () => {
+    app.init();
+});