diff --git a/backend/internal/models/models.go b/backend/internal/models/models.go
new file mode 100644
index 0000000..add5a36
--- /dev/null
+++ b/backend/internal/models/models.go
@@ -0,0 +1,114 @@
+package models
+
+import (
+	"time"
+)
+
+// ExerciseType represents the type of exercise
+type ExerciseType string
+
+const (
+	ExerciseTypeStrength ExerciseType = "strength"
+	ExerciseTypeCardio   ExerciseType = "cardio"
+)
+
+// Exercise represents an exercise definition
+type Exercise struct {
+	ID          int64        `json:"id"`
+	Name        string       `json:"name"`
+	Type        ExerciseType `json:"type"`
+	MuscleGroup string       `json:"muscle_group,omitempty"`
+	Description string       `json:"description,omitempty"`
+	CreatedAt   time.Time    `json:"created_at"`
+}
+
+// TrainingPlan represents a training plan template
+type TrainingPlan struct {
+	ID          int64          `json:"id"`
+	Name        string         `json:"name"`
+	Description string         `json:"description,omitempty"`
+	Exercises   []PlanExercise `json:"exercises,omitempty"`
+	CreatedAt   time.Time      `json:"created_at"`
+}
+
+// PlanExercise represents an exercise within a training plan
+type PlanExercise struct {
+	ID         int64    `json:"id"`
+	PlanID     int64    `json:"plan_id"`
+	ExerciseID int64    `json:"exercise_id"`
+	Exercise   Exercise `json:"exercise,omitempty"`
+	Sets       int      `json:"sets,omitempty"`
+	Reps       int      `json:"reps,omitempty"`
+	Duration   int      `json:"duration,omitempty"` // in seconds
+	Order      int      `json:"order"`
+}
+
+// Session represents a completed training session
+type Session struct {
+	ID        int64          `json:"id"`
+	PlanID    *int64         `json:"plan_id,omitempty"`
+	Plan      *TrainingPlan  `json:"plan,omitempty"`
+	Date      time.Time      `json:"date"`
+	Notes     string         `json:"notes,omitempty"`
+	Entries   []SessionEntry `json:"entries,omitempty"`
+	CreatedAt time.Time      `json:"created_at"`
+}
+
+// SessionEntry represents an individual exercise entry in a session
+type SessionEntry struct {
+	ID            int64     `json:"id"`
+	SessionID     int64     `json:"session_id"`
+	ExerciseID    int64     `json:"exercise_id"`
+	Exercise      *Exercise `json:"exercise,omitempty"`
+	Weight        float64   `json:"weight,omitempty"`        // in kg
+	Reps          int       `json:"reps,omitempty"`          // for strength
+	SetsCompleted int       `json:"sets_completed,omitempty"`
+	Duration      int       `json:"duration,omitempty"`      // in seconds, for cardio
+	Distance      float64   `json:"distance,omitempty"`      // in km, for cardio
+	HeartRate     int       `json:"heart_rate,omitempty"`    // average HR
+	Notes         string    `json:"notes,omitempty"`
+	CreatedAt     time.Time `json:"created_at"`
+}
+
+// CreateExerciseRequest represents the request to create an exercise
+type CreateExerciseRequest struct {
+	Name        string       `json:"name"`
+	Type        ExerciseType `json:"type"`
+	MuscleGroup string       `json:"muscle_group,omitempty"`
+	Description string       `json:"description,omitempty"`
+}
+
+// CreatePlanRequest represents the request to create a training plan
+type CreatePlanRequest struct {
+	Name        string               `json:"name"`
+	Description string               `json:"description,omitempty"`
+	Exercises   []PlanExerciseInput  `json:"exercises,omitempty"`
+}
+
+// PlanExerciseInput represents exercise input for plan creation
+type PlanExerciseInput struct {
+	ExerciseID int64 `json:"exercise_id"`
+	Sets       int   `json:"sets,omitempty"`
+	Reps       int   `json:"reps,omitempty"`
+	Duration   int   `json:"duration,omitempty"`
+	Order      int   `json:"order"`
+}
+
+// CreateSessionRequest represents the request to create a session
+type CreateSessionRequest struct {
+	PlanID *int64    `json:"plan_id,omitempty"`
+	Date   time.Time `json:"date"`
+	Notes  string    `json:"notes,omitempty"`
+}
+
+// CreateSessionEntryRequest represents the request to add an entry to a session
+type CreateSessionEntryRequest struct {
+	ExerciseID    int64   `json:"exercise_id"`
+	Weight        float64 `json:"weight,omitempty"`
+	Reps          int     `json:"reps,omitempty"`
+	SetsCompleted int     `json:"sets_completed,omitempty"`
+	Duration      int     `json:"duration,omitempty"`
+	Distance      float64 `json:"distance,omitempty"`
+	HeartRate     int     `json:"heart_rate,omitempty"`
+	Notes         string  `json:"notes,omitempty"`
+}
diff --git a/backend/internal/storage/db.go b/backend/internal/storage/db.go
new file mode 100644
index 0000000..8addade
--- /dev/null
+++ b/backend/internal/storage/db.go
@@ -0,0 +1,109 @@
+package storage
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"os"
+
+	_ "github.com/lib/pq"
+)
+
+type DB struct {
+	*sql.DB
+}
+
+func NewDB(ctx context.Context) (*DB, error) {
+	host := getEnv("DB_HOST", "localhost")
+	port := getEnv("DB_PORT", "5432")
+	user := getEnv("DB_USER", "postgres")
+	password := getEnv("DB_PASSWORD", "postgres")
+	dbname := getEnv("DB_NAME", "training_tracker")
+
+	connStr := fmt.Sprintf(
+		"host=%s port=%s user=%s password=%s dbname=%s sslmode=disable",
+		host, port, user, password, dbname,
+	)
+
+	db, err := openDB(connStr)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := db.PingContext(ctx); err != nil {
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	return &DB{db}, nil
+}
+
+func openDB(connStr string) (*sql.DB, error) {
+	db, err := sql.Open("postgres", connStr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %w", err)
+	}
+	return db, nil
+}
+
+func (db *DB) Migrate(ctx context.Context) error {
+	migrations := []string{
+		`CREATE TABLE IF NOT EXISTS exercises (
+			id SERIAL PRIMARY KEY,
+			name VARCHAR(255) NOT NULL,
+			type VARCHAR(50) NOT NULL,
+			muscle_group VARCHAR(100),
+			description TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS training_plans (
+			id SERIAL PRIMARY KEY,
+			name VARCHAR(255) NOT NULL,
+			description TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS plan_exercises (
+			id SERIAL PRIMARY KEY,
+			plan_id INTEGER REFERENCES training_plans(id) ON DELETE CASCADE,
+			exercise_id INTEGER REFERENCES exercises(id) ON DELETE CASCADE,
+			sets INTEGER,
+			reps INTEGER,
+			duration INTEGER,
+			sort_order INTEGER DEFAULT 0
+		)`,
+		`CREATE TABLE IF NOT EXISTS sessions (
+			id SERIAL PRIMARY KEY,
+			plan_id INTEGER REFERENCES training_plans(id) ON DELETE SET NULL,
+			date TIMESTAMP NOT NULL,
+			notes TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS session_entries (
+			id SERIAL PRIMARY KEY,
+			session_id INTEGER REFERENCES sessions(id) ON DELETE CASCADE,
+			exercise_id INTEGER REFERENCES exercises(id) ON DELETE CASCADE,
+			weight DECIMAL(10, 2),
+			reps INTEGER,
+			sets_completed INTEGER,
+			duration INTEGER,
+			distance DECIMAL(10, 2),
+			heart_rate INTEGER,
+			notes TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+	}
+
+	for _, migration := range migrations {
+		if _, err := db.ExecContext(ctx, migration); err != nil {
+			return fmt.Errorf("migration failed: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func getEnv(key, defaultValue string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return defaultValue
+}
diff --git a/backend/internal/storage/exercises.go b/backend/internal/storage/exercises.go
new file mode 100644
index 0000000..efe294a
--- /dev/null
+++ b/backend/internal/storage/exercises.go
@@ -0,0 +1,121 @@
+package storage
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"training-tracker/internal/models"
+)
+
+type ExerciseRepository struct {
+	db *DB
+}
+
+func NewExerciseRepository(db *DB) *ExerciseRepository {
+	return &ExerciseRepository{db: db}
+}
+
+func (r *ExerciseRepository) List(ctx context.Context) ([]models.Exercise, error) {
+	query := `SELECT id, name, type, muscle_group, description, created_at
+			  FROM exercises ORDER BY name`
+
+	rows, err := r.db.QueryContext(ctx, query)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query exercises: %w", err)
+	}
+	defer rows.Close()
+
+	var exercises []models.Exercise
+	for rows.Next() {
+		var e models.Exercise
+		var muscleGroup, description sql.NullString
+		if err := rows.Scan(&e.ID, &e.Name, &e.Type, &muscleGroup, &description, &e.CreatedAt); err != nil {
+			return nil, fmt.Errorf("failed to scan exercise: %w", err)
+		}
+		e.MuscleGroup = muscleGroup.String
+		e.Description = description.String
+		exercises = append(exercises, e)
+	}
+
+	return exercises, nil
+}
+
+func (r *ExerciseRepository) GetByID(ctx context.Context, id int64) (*models.Exercise, error) {
+	query := `SELECT id, name, type, muscle_group, description, created_at
+			  FROM exercises WHERE id = $1`
+
+	var e models.Exercise
+	var muscleGroup, description sql.NullString
+	err := r.db.QueryRowContext(ctx, query, id).Scan(&e.ID, &e.Name, &e.Type, &muscleGroup, &description, &e.CreatedAt)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to get exercise: %w", err)
+	}
+	e.MuscleGroup = muscleGroup.String
+	e.Description = description.String
+
+	return &e, nil
+}
+
+func (r *ExerciseRepository) Create(ctx context.Context, req *models.CreateExerciseRequest) (*models.Exercise, error) {
+	query := `INSERT INTO exercises (name, type, muscle_group, description)
+			  VALUES ($1, $2, $3, $4)
+			  RETURNING id, name, type, muscle_group, description, created_at`
+
+	var e models.Exercise
+	var muscleGroup, description sql.NullString
+	err := r.db.QueryRowContext(ctx, query, req.Name, req.Type, nullString(req.MuscleGroup), nullString(req.Description)).
+		Scan(&e.ID, &e.Name, &e.Type, &muscleGroup, &description, &e.CreatedAt)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create exercise: %w", err)
+	}
+	e.MuscleGroup = muscleGroup.String
+	e.Description = description.String
+
+	return &e, nil
+}
+
+func (r *ExerciseRepository) Update(ctx context.Context, id int64, req *models.CreateExerciseRequest) (*models.Exercise, error) {
+	query := `UPDATE exercises
+			  SET name = $1, type = $2, muscle_group = $3, description = $4
+			  WHERE id = $5
+			  RETURNING id, name, type, muscle_group, description, created_at`
+
+	var e models.Exercise
+	var muscleGroup, description sql.NullString
+	err := r.db.QueryRowContext(ctx, query, req.Name, req.Type, nullString(req.MuscleGroup), nullString(req.Description), id).
+		Scan(&e.ID, &e.Name, &e.Type, &muscleGroup, &description, &e.CreatedAt)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to update exercise: %w", err)
+	}
+	e.MuscleGroup = muscleGroup.String
+	e.Description = description.String
+
+	return &e, nil
+}
+
+func (r *ExerciseRepository) Delete(ctx context.Context, id int64) error {
+	query := `DELETE FROM exercises WHERE id = $1`
+	result, err := r.db.ExecContext(ctx, query, id)
+	if err != nil {
+		return fmt.Errorf("failed to delete exercise: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}
+
+func nullString(s string) sql.NullString {
+	if s == "" {
+		return sql.NullString{}
+	}
+	return sql.NullString{String: s, Valid: true}
+}
diff --git a/backend/internal/storage/plans.go b/backend/internal/storage/plans.go
new file mode 100644
index 0000000..f900ea9
--- /dev/null
+++ b/backend/internal/storage/plans.go
@@ -0,0 +1,183 @@
+package storage
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"training-tracker/internal/models"
+)
+
+type PlanRepository struct {
+	db *DB
+}
+
+func NewPlanRepository(db *DB) *PlanRepository {
+	return &PlanRepository{db: db}
+}
+
+func (r *PlanRepository) List(ctx context.Context) ([]models.TrainingPlan, error) {
+	query := `SELECT id, name, description, created_at FROM training_plans ORDER BY name`
+
+	rows, err := r.db.QueryContext(ctx, query)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query plans: %w", err)
+	}
+	defer rows.Close()
+
+	var plans []models.TrainingPlan
+	for rows.Next() {
+		var p models.TrainingPlan
+		var description sql.NullString
+		if err := rows.Scan(&p.ID, &p.Name, &description, &p.CreatedAt); err != nil {
+			return nil, fmt.Errorf("failed to scan plan: %w", err)
+		}
+		p.Description = description.String
+		plans = append(plans, p)
+	}
+
+	return plans, nil
+}
+
+func (r *PlanRepository) GetByID(ctx context.Context, id int64) (*models.TrainingPlan, error) {
+	query := `SELECT id, name, description, created_at FROM training_plans WHERE id = $1`
+
+	var p models.TrainingPlan
+	var description sql.NullString
+	err := r.db.QueryRowContext(ctx, query, id).Scan(&p.ID, &p.Name, &description, &p.CreatedAt)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to get plan: %w", err)
+	}
+	p.Description = description.String
+
+	exerciseQuery := `
+		SELECT pe.id, pe.plan_id, pe.exercise_id, pe.sets, pe.reps, pe.duration, pe.sort_order,
+			   e.id, e.name, e.type, e.muscle_group, e.description, e.created_at
+		FROM plan_exercises pe
+		JOIN exercises e ON pe.exercise_id = e.id
+		WHERE pe.plan_id = $1
+		ORDER BY pe.sort_order`
+
+	rows, err := r.db.QueryContext(ctx, exerciseQuery, id)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query plan exercises: %w", err)
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var pe models.PlanExercise
+		var sets, reps, duration sql.NullInt64
+		var muscleGroup, exerciseDesc sql.NullString
+		if err := rows.Scan(
+			&pe.ID, &pe.PlanID, &pe.ExerciseID, &sets, &reps, &duration, &pe.Order,
+			&pe.Exercise.ID, &pe.Exercise.Name, &pe.Exercise.Type, &muscleGroup, &exerciseDesc, &pe.Exercise.CreatedAt,
+		); err != nil {
+			return nil, fmt.Errorf("failed to scan plan exercise: %w", err)
+		}
+		pe.Sets = int(sets.Int64)
+		pe.Reps = int(reps.Int64)
+		pe.Duration = int(duration.Int64)
+		pe.Exercise.MuscleGroup = muscleGroup.String
+		pe.Exercise.Description = exerciseDesc.String
+		p.Exercises = append(p.Exercises, pe)
+	}
+
+	return &p, nil
+}
+
+func (r *PlanRepository) Create(ctx context.Context, req *models.CreatePlanRequest) (*models.TrainingPlan, error) {
+	tx, err := r.db.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer tx.Rollback()
+
+	query := `INSERT INTO training_plans (name, description)
+			  VALUES ($1, $2)
+			  RETURNING id, name, description, created_at`
+
+	var p models.TrainingPlan
+	var description sql.NullString
+	err = tx.QueryRowContext(ctx, query, req.Name, nullString(req.Description)).
+		Scan(&p.ID, &p.Name, &description, &p.CreatedAt)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create plan: %w", err)
+	}
+	p.Description = description.String
+
+	for _, pe := range req.Exercises {
+		exerciseQuery := `INSERT INTO plan_exercises (plan_id, exercise_id, sets, reps, duration, sort_order)
+						  VALUES ($1, $2, $3, $4, $5, $6)`
+		_, err = tx.ExecContext(ctx, exerciseQuery, p.ID, pe.ExerciseID, nullInt(pe.Sets), nullInt(pe.Reps), nullInt(pe.Duration), pe.Order)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create plan exercise: %w", err)
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
+	return r.GetByID(ctx, p.ID)
+}
+
+func (r *PlanRepository) Update(ctx context.Context, id int64, req *models.CreatePlanRequest) (*models.TrainingPlan, error) {
+	tx, err := r.db.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer tx.Rollback()
+
+	query := `UPDATE training_plans SET name = $1, description = $2 WHERE id = $3`
+	result, err := tx.ExecContext(ctx, query, req.Name, nullString(req.Description), id)
+	if err != nil {
+		return nil, fmt.Errorf("failed to update plan: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return nil, nil
+	}
+
+	_, err = tx.ExecContext(ctx, `DELETE FROM plan_exercises WHERE plan_id = $1`, id)
+	if err != nil {
+		return nil, fmt.Errorf("failed to delete plan exercises: %w", err)
+	}
+
+	for _, pe := range req.Exercises {
+		exerciseQuery := `INSERT INTO plan_exercises (plan_id, exercise_id, sets, reps, duration, sort_order)
+						  VALUES ($1, $2, $3, $4, $5, $6)`
+		_, err = tx.ExecContext(ctx, exerciseQuery, id, pe.ExerciseID, nullInt(pe.Sets), nullInt(pe.Reps), nullInt(pe.Duration), pe.Order)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create plan exercise: %w", err)
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
+	return r.GetByID(ctx, id)
+}
+
+func (r *PlanRepository) Delete(ctx context.Context, id int64) error {
+	query := `DELETE FROM training_plans WHERE id = $1`
+	result, err := r.db.ExecContext(ctx, query, id)
+	if err != nil {
+		return fmt.Errorf("failed to delete plan: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}
+
+func nullInt(i int) sql.NullInt64 {
+	if i == 0 {
+		return sql.NullInt64{}
+	}
+	return sql.NullInt64{Int64: int64(i), Valid: true}
+}
diff --git a/backend/internal/storage/sessions.go b/backend/internal/storage/sessions.go
new file mode 100644
index 0000000..fd5938f
--- /dev/null
+++ b/backend/internal/storage/sessions.go
@@ -0,0 +1,239 @@
+package storage
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"training-tracker/internal/models"
+)
+
+type SessionRepository struct {
+	db *DB
+}
+
+func NewSessionRepository(db *DB) *SessionRepository {
+	return &SessionRepository{db: db}
+}
+
+func (r *SessionRepository) List(ctx context.Context) ([]models.Session, error) {
+	query := `
+		SELECT s.id, s.plan_id, s.date, s.notes, s.created_at,
+			   p.id, p.name, p.description, p.created_at
+		FROM sessions s
+		LEFT JOIN training_plans p ON s.plan_id = p.id
+		ORDER BY s.date DESC`
+
+	rows, err := r.db.QueryContext(ctx, query)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query sessions: %w", err)
+	}
+	defer rows.Close()
+
+	var sessions []models.Session
+	for rows.Next() {
+		var s models.Session
+		var planID sql.NullInt64
+		var notes sql.NullString
+		var planIDVal, planName, planDesc sql.NullString
+		var planCreatedAt sql.NullTime
+
+		if err := rows.Scan(
+			&s.ID, &planID, &s.Date, &notes, &s.CreatedAt,
+			&planIDVal, &planName, &planDesc, &planCreatedAt,
+		); err != nil {
+			return nil, fmt.Errorf("failed to scan session: %w", err)
+		}
+		s.Notes = notes.String
+		if planID.Valid {
+			pid := planID.Int64
+			s.PlanID = &pid
+			s.Plan = &models.TrainingPlan{
+				ID:          pid,
+				Name:        planName.String,
+				Description: planDesc.String,
+				CreatedAt:   planCreatedAt.Time,
+			}
+		}
+		sessions = append(sessions, s)
+	}
+
+	return sessions, nil
+}
+
+func (r *SessionRepository) GetByID(ctx context.Context, id int64) (*models.Session, error) {
+	query := `
+		SELECT s.id, s.plan_id, s.date, s.notes, s.created_at,
+			   p.id, p.name, p.description, p.created_at
+		FROM sessions s
+		LEFT JOIN training_plans p ON s.plan_id = p.id
+		WHERE s.id = $1`
+
+	var s models.Session
+	var planID sql.NullInt64
+	var notes sql.NullString
+	var planIDVal, planName, planDesc sql.NullString
+	var planCreatedAt sql.NullTime
+
+	err := r.db.QueryRowContext(ctx, query, id).Scan(
+		&s.ID, &planID, &s.Date, &notes, &s.CreatedAt,
+		&planIDVal, &planName, &planDesc, &planCreatedAt,
+	)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("failed to get session: %w", err)
+	}
+	s.Notes = notes.String
+	if planID.Valid {
+		pid := planID.Int64
+		s.PlanID = &pid
+		s.Plan = &models.TrainingPlan{
+			ID:          pid,
+			Name:        planName.String,
+			Description: planDesc.String,
+			CreatedAt:   planCreatedAt.Time,
+		}
+	}
+
+	entriesQuery := `
+		SELECT se.id, se.session_id, se.exercise_id, se.weight, se.reps, se.sets_completed,
+			   se.duration, se.distance, se.heart_rate, se.notes, se.created_at,
+			   e.id, e.name, e.type, e.muscle_group, e.description, e.created_at
+		FROM session_entries se
+		JOIN exercises e ON se.exercise_id = e.id
+		WHERE se.session_id = $1
+		ORDER BY se.created_at`
+
+	rows, err := r.db.QueryContext(ctx, entriesQuery, id)
+	if err != nil {
+		return nil, fmt.Errorf("failed to query session entries: %w", err)
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var se models.SessionEntry
+		var weight, distance sql.NullFloat64
+		var reps, setsCompleted, duration, heartRate sql.NullInt64
+		var entryNotes, muscleGroup, exerciseDesc sql.NullString
+		var exercise models.Exercise
+
+		if err := rows.Scan(
+			&se.ID, &se.SessionID, &se.ExerciseID, &weight, &reps, &setsCompleted,
+			&duration, &distance, &heartRate, &entryNotes, &se.CreatedAt,
+			&exercise.ID, &exercise.Name, &exercise.Type, &muscleGroup, &exerciseDesc, &exercise.CreatedAt,
+		); err != nil {
+			return nil, fmt.Errorf("failed to scan session entry: %w", err)
+		}
+		se.Weight = weight.Float64
+		se.Reps = int(reps.Int64)
+		se.SetsCompleted = int(setsCompleted.Int64)
+		se.Duration = int(duration.Int64)
+		se.Distance = distance.Float64
+		se.HeartRate = int(heartRate.Int64)
+		se.Notes = entryNotes.String
+		exercise.MuscleGroup = muscleGroup.String
+		exercise.Description = exerciseDesc.String
+		se.Exercise = &exercise
+		s.Entries = append(s.Entries, se)
+	}
+
+	return &s, nil
+}
+
+func (r *SessionRepository) Create(ctx context.Context, req *models.CreateSessionRequest) (*models.Session, error) {
+	query := `INSERT INTO sessions (plan_id, date, notes)
+			  VALUES ($1, $2, $3)
+			  RETURNING id, plan_id, date, notes, created_at`
+
+	var s models.Session
+	var planID sql.NullInt64
+	var notes sql.NullString
+
+	var reqPlanID sql.NullInt64
+	if req.PlanID != nil {
+		reqPlanID = sql.NullInt64{Int64: *req.PlanID, Valid: true}
+	}
+
+	err := r.db.QueryRowContext(ctx, query, reqPlanID, req.Date, nullString(req.Notes)).
+		Scan(&s.ID, &planID, &s.Date, &notes, &s.CreatedAt)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create session: %w", err)
+	}
+	s.Notes = notes.String
+	if planID.Valid {
+		pid := planID.Int64
+		s.PlanID = &pid
+	}
+
+	return &s, nil
+}
+
+func (r *SessionRepository) Update(ctx context.Context, id int64, req *models.CreateSessionRequest) (*models.Session, error) {
+	var reqPlanID sql.NullInt64
+	if req.PlanID != nil {
+		reqPlanID = sql.NullInt64{Int64: *req.PlanID, Valid: true}
+	}
+
+	query := `UPDATE sessions SET plan_id = $1, date = $2, notes = $3 WHERE id = $4`
+	result, err := r.db.ExecContext(ctx, query, reqPlanID, req.Date, nullString(req.Notes), id)
+	if err != nil {
+		return nil, fmt.Errorf("failed to update session: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return nil, nil
+	}
+
+	return r.GetByID(ctx, id)
+}
+
+func (r *SessionRepository) Delete(ctx context.Context, id int64) error {
+	query := `DELETE FROM sessions WHERE id = $1`
+	result, err := r.db.ExecContext(ctx, query, id)
+	if err != nil {
+		return fmt.Errorf("failed to delete session: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}
+
+func (r *SessionRepository) AddEntry(ctx context.Context, sessionID int64, req *models.CreateSessionEntryRequest) (*models.SessionEntry, error) {
+	query := `INSERT INTO session_entries (session_id, exercise_id, weight, reps, sets_completed, duration, distance, heart_rate, notes)
+			  VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
+			  RETURNING id, session_id, exercise_id, weight, reps, sets_completed, duration, distance, heart_rate, notes, created_at`
+
+	var se models.SessionEntry
+	var weight, distance sql.NullFloat64
+	var reps, setsCompleted, duration, heartRate sql.NullInt64
+	var notes sql.NullString
+
+	err := r.db.QueryRowContext(ctx, query, sessionID, req.ExerciseID,
+		nullFloat(req.Weight), nullInt(req.Reps), nullInt(req.SetsCompleted),
+		nullInt(req.Duration), nullFloat(req.Distance), nullInt(req.HeartRate),
+		nullString(req.Notes)).
+		Scan(&se.ID, &se.SessionID, &se.ExerciseID, &weight, &reps, &setsCompleted, &duration, &distance, &heartRate, &notes, &se.CreatedAt)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create session entry: %w", err)
+	}
+	se.Weight = weight.Float64
+	se.Reps = int(reps.Int64)
+	se.SetsCompleted = int(setsCompleted.Int64)
+	se.Duration = int(duration.Int64)
+	se.Distance = distance.Float64
+	se.HeartRate = int(heartRate.Int64)
+	se.Notes = notes.String
+
+	return &se, nil
+}
+
+func nullFloat(f float64) sql.NullFloat64 {
+	if f == 0 {
+		return sql.NullFloat64{}
+	}
+	return sql.NullFloat64{Float64: f, Valid: true}
+}