Stroke Mechanics
The Biomechanics of Swimming Speed
The Fundamental Equation of Swimming Speed
The Velocity Equation
Translation: How fast you swim depends on how often you stroke (SR) multiplied by how far you travel per stroke (DPS).
This deceptively simple equation governs all swimming performance. To get faster, you must either:
- Increase Stroke Rate (turnover faster) while maintaining DPS
- Increase Distance Per Stroke (travel farther per stroke) while maintaining SR
- Optimize both (the ideal approach)
⚖️ The Trade-off
SR and DPS are generally inversely related. As one increases, the other tends to decrease. The art of swimming is finding the optimal balance for your event, body type, and current fitness level.
Stroke Rate (SR)
What is Stroke Rate?
Stroke Rate (SR), also called cadence or tempo, measures how many complete stroke cycles you perform per minute, expressed in Strokes Per Minute (SPM).
Formula
Or:
Example:
If your stroke cycle takes 1 second:
If you complete 30 strokes in 25 seconds:
📝 Stroke Counting Note
For freestyle/backstroke: Count individual arm entries (left + right = 2 strokes)
For breaststroke/butterfly: Arms move simultaneously (one pull = 1 stroke)
Typical Stroke Rates by Event
Freestyle Sprint (50m)
Freestyle 100m
Middle Distance (200-800m)
Distance (1500m+ / Open Water)
🎯 Gender Differences
Elite male 50m free: ~65-70 SPM
Elite female 50m free: ~60-64 SPM
Elite male 100m free: ~50-54 SPM
Elite female 100m free: ~53-56 SPM
Interpreting Stroke Rate
🐢 SR Too Low
Characteristics:
- Long glide phases between strokes
- Deceleration and momentum loss
- "Dead spots" where velocity drops significantly
Result: Inefficient energy use—you're constantly re-accelerating from reduced speed.
Fix: Reduce glide time, initiate catch earlier, maintain continuous propulsion.
🏃 SR Too High
Characteristics:
- Short, choppy strokes ("spinning wheels")
- Poor catch mechanics—hand slipping past water
- Excessive energy expenditure for minimal propulsion
Result: High effort, low efficiency. Feels busy but not fast.
Fix: Lengthen stroke, improve catch, ensure full extension and push-through.
⚡ Optimal SR
Characteristics:
- Balanced rhythm—continuous but not frantic
- Minimal deceleration between strokes
- Strong catch and full extension
- Sustainable at race pace
Result: Maximum velocity with minimum wasted energy.
How to Find: Experiment with ±5 SPM adjustments while maintaining pace. Lowest RPE = optimal SR.
Distance Per Stroke (DPS)
What is Distance Per Stroke?
Distance Per Stroke (DPS), also called Stroke Length, measures how far you travel with each complete stroke cycle. It's a primary indicator of stroke efficiency and "feel for the water."
Formula
Or:
Example (25m pool, 5m push-off):
Swim 20m in 12 strokes:
For 100m with 48 strokes (4 × 5m push-offs):
DPS = 80 / 48 = 1.67 m/stroke
Typical DPS Values (25m Pool Freestyle)
Elite Swimmers
Competitive Swimmers
Fitness Swimmers
Beginners
📏 Height Adjustments
6'0" (183cm): Target ~12 strokes/25m
5'6" (168cm): Target ~13 strokes/25m
5'0" (152cm): Target ~14 strokes/25m
Taller swimmers naturally have longer DPS due to arm length and body size.
Factors Affecting DPS
1️⃣ Catch Quality
The ability to "hold" water with your hand and forearm during the pull phase. A strong catch = more propulsion per stroke.
Drill: Catch-up drill, fist swimming, sculling exercises.
2️⃣ Stroke Completion
Pushing all the way through to full extension at the hip. Many swimmers release early, losing the final 20% of propulsion.
Drill: Fingertip drag drill, extension focus sets.
3️⃣ Body Position & Streamline
Reduced drag = farther travel per stroke. High hips, horizontal body, tight core all minimize resistance.
Drill: Kick on side, streamline push-offs, core stability work.
4️⃣ Kick Effectiveness
The kick maintains velocity between arm strokes. Weak kick = deceleration = shorter DPS.
Drill: Vertical kicking, kick with board, kick on side.
5️⃣ Breathing Technique
Poor breathing disrupts body position and creates drag. Minimize head movement and rotation.
Drill: Side breathing drill, bilateral breathing, breathing every 3/5 strokes.
The SR × DPS Balance
Elite swimmers don't just have high SR or high DPS—they have the optimal combination for their event.
Real-World Example: Caeleb Dressel's 50m Freestyle
World Record Metrics:
- Stroke Rate: ~130 strokes/min
- Distance Per Stroke: ~0.92 yards/stroke (~0.84 m/stroke)
- Velocity: ~2.3 m/s (world record pace)
Analysis: Dressel combines exceptionally high SR with good DPS. His power allows him to maintain reasonable stroke length despite extreme turnover.
Scenario Analysis
🔴 High DPS + Low SR = "Overgliding"
Example: 1.8 m/stroke × 50 SPM = 1.5 m/s
Problem: Too much glide creates dead spots where velocity drops. Inefficient despite good stroke length.
🔴 Low DPS + High SR = "Spinning Wheels"
Example: 1.2 m/stroke × 90 SPM = 1.8 m/s
Problem: High energy cost. Feels busy but lacks propulsion per stroke. Unsustainable.
🟢 Balanced DPS + SR = Optimal
Example: 1.6 m/stroke × 70 SPM = 1.87 m/s
Result: Strong propulsion per stroke with sustainable turnover. Efficient and fast.
✅ Finding Your Optimal Balance
Set: 6 × 100m @ CSS pace
- 100 #1-2: Swim naturally, record SR and DPS
- 100 #3: Reduce stroke count by 2-3 (increase DPS), try to maintain pace
- 100 #4: Increase SR by 5 SPM, try to maintain pace
- 100 #5: Find middle ground—balance SR and DPS
- 100 #6: Lock in on what felt most efficient
The rep that felt easiest at pace = your optimal SR/DPS combination.
Stroke Index: The Power-Efficiency Metric
Formula
Stroke Index combines speed and efficiency into one metric. Higher SI = better performance.
Example:
Swimmer A: 1.5 m/s velocity × 1.7 m/stroke DPS = SI of 2.55
Swimmer B: 1.4 m/s velocity × 1.9 m/stroke DPS = SI of 2.66
Analysis: Swimmer B is slightly slower but more efficient. With improved power, they have higher performance potential.
🔬 Research Foundation
Barbosa et al. (2010) found that stroke length is a more important predictor of performance than stroke rate in competitive swimming. However, the relationship isn't linear—there's an optimal point beyond which increasing DPS (by decreasing SR) becomes counterproductive due to lost momentum.
The key is biomechanical efficiency: maximizing propulsion per stroke while maintaining rhythm that prevents deceleration.
Practical Training Applications
🎯 SR Control Set
8 × 50m (20s rest)
Use a Tempo Trainer or count strokes/time
- 50 #1-2: Baseline SR (swim naturally)
- 50 #3-4: SR +10 SPM (faster turnover)
- 50 #5-6: SR -10 SPM (slower, longer strokes)
- 50 #7-8: Return to baseline, note which felt most efficient
Goal: Develop awareness of how SR changes affect pace and effort.
🎯 DPS Maximization Set
8 × 25m (15s rest)
Count strokes per length
- 25 #1: Establish baseline stroke count
- 25 #2-4: Reduce by 1 stroke per lap (max DPS)
- 25 #5: Hold minimum stroke count, increase pace slightly
- 25 #6-8: Find sustainable reduced stroke count at target pace
Goal: Improve stroke efficiency—travel farther per stroke without slowing down.
🎯 Golf Set (Minimize SWOLF)
4 × 100m (30s rest)
Goal: Lowest SWOLF score (time + strokes) at CSS pace
Experiment with different SR/DPS combinations. The rep with lowest SWOLF = most efficient.
Track how SWOLF changes across reps—rising SWOLF indicates fatigue breaking down technique.
Master the Mechanics, Master the Speed
Velocity = SR × DPS isn't just a formula—it's a framework for understanding and improving every aspect of your swimming technique.
Track both variables. Experiment with the balance. Find your optimal combination. Speed will follow.