Overview
This lecture discusses how optimal stride frequency (SF) for running, which minimizes heart rate (HR) and energy use, relates to speed in inexperienced runners, and evaluates whether SF should be adjusted as speed changes.
Stride Frequency and Running Economy
- Running speed equals stride frequency (SF) times stride length (SL); both increase with running speed.
- SF is measured in strides per minute (spm) and influences running biomechanics and energy expenditure.
- Optimal SF (SF opt) minimizes energy cost at a given speed, but self-selected SF (SF self) is often lower, especially in inexperienced runners.
Previous Findings and Hypotheses
- It is commonly advised to run at 90 spm, but this may be higher than needed for most runners.
- Experienced runners typically select SF close to SF opt; inexperienced runners select lower SF than their optimum.
- Hypotheses: (1) SF-HR forms a parabola at each speed; (2) SF opt increases with speed; (3) Parabola flattens at higher speeds; (4) Inexperienced runners run below SF opt.
Methods
- Twelve inexperienced runners ran on treadmills at 90%, 100%, and 110% of their self-selected speed.
- At each speed, they ran at various imposed SFs and their self-selected SF.
- HR and SF were measured, and models tested the relationship between SF, speed, and HR.
Results
- The SF-HR relationship was parabolic at all speeds, with a stable SF opt (~83 spm).
- SF opt did not significantly increase with speed, nor did the parabolic curve flatten at higher speeds.
- At all speeds, most runners chose SF self below SF opt, suggesting room for efficiency improvement.
- Participants found it hardest to maintain extreme imposed SFs (very high or very low).
Discussion and Implications
- Unlike common advice, SF opt for inexperienced runners is typically lower than 90 spm and consistent across moderate speeds.
- Increasing SF closer to 83 spm may reduce HR and energy use for most inexperienced runners.
- Large individual variation means SF advice should be individualized, not generalized.
- Factors like coordination, fatigue, footwear, and environment can affect SF self.
Key Terms & Definitions
- Stride Frequency (SF) — The number of strides taken per minute.
- Stride Length (SL) — The length of each stride.
- SF Optimum (SF opt) — The stride frequency that minimizes energy expenditure or HR at a given speed.
- Self-selected SF (SF self) — The stride frequency a runner naturally chooses.
- Heart Rate (HR) — Number of heartbeats per minute, used as a proxy for energy expenditure.
Action Items / Next Steps
- If running between 2.4–2.9 m/s, try increasing stride frequency toward 83 spm for potentially lower HR.
- Use personal running data (SF, HR, speed) to determine individual SF opt.
- Further research: test over a wider speed range and in experienced runners; investigate why runners under-select SF.