BLUF (Bottom Line Up Front)
A study on British Army personnel found that 1.5-mile run time and body mass are the most reliable predictors of 8-mile Loaded March (LM) performance, regardless of sex. The research highlights that aerobic fitness and weight are critical factors for load-carrying capability, while muscular strength (e.g., lift capacity) adds little predictive value. Women demonstrated lower overall performance metrics compared to men but showed overlap in individual capabilities.
Purpose of the Study
- The study aimed to develop a model predicting 8-mile Loaded March (LM) performance and assess the physical performance differences between men and women in the British Army.
Testing Protocols
- Participants: 135 soldiers (87 men, 48 women).
- Session 1 Tests:
- 1.5-Mile Run: A timed run to evaluate aerobic capacity.
- Max Single Lift (SL): Lifting a weighted Powerbag™ to a 4.75-foot platform for maximum weight.
- Water Can Carry (WCC): Carrying two 44-lb water cans until exhaustion.
- Body mass, fat-free mass, and height measurements were taken using a DXA scan.
- Session 2 Test:
- 8-Mile Loaded March (LM): Carried a 55-lb load over 8 miles. The first 4 miles were completed at a prescribed pace of 4 mph (5.8 ft/s), and the last 4 miles were completed at a self-selected maximum pace.
Key Findings
- The best predictors of LM performance were 1.5-mile run time and body mass, explaining 71% of the variance (R² = 0.71).
- Adding muscular endurance (WCC) or strength (SL) tests provided limited additional value to the prediction model.
- The Single Lift (SL), designed to measure maximal strength, had minimal influence on LM performance.
- The WCC, a proxy for muscular endurance, also contributed minimally to LM performance prediction. Although relevant for some operational tasks, muscular endurance did not significantly impact long-distance rucking performance.
Performance Metrics Comparison Between Men and Women
1.5-Mile Run Times and Loaded March Success
- Average Run Times for Successful Participants:
- Men: 9.7 minutes
- Women: 10.9 minutes
- Combined Average: 10.0 minutes
- Run Times for Failed Participants:
- Women Who Failed: 12.5 minutes
- Women Who Did Not Finish (DNF): 12.2 minutes
- Key Insight: Participants with slower 1.5-mile run times (e.g., exceeding 12 minutes for women) were significantly more likely to fail or not complete the LM, emphasizing the importance of aerobic fitness.
Body Mass and Loaded March Success
- Average Body Mass for Successful Participants:
- Men: 173.6 lbs (78.7 kg)
- Women: 144.8 lbs (65.7 kg)
- Combined Average: 165.8 lbs (75.2 kg)
- Body Mass for Failed Participants:
- Women Who Failed: 146.9 lbs (66.6 kg)
- Women Who Did Not Finish (DNF): 140 lbs (63.6 kg)
- Key Insight: Higher body mass was beneficial for LM success when paired with strong aerobic capacity, as lean mass helped support load carriage. However, excessive mass without sufficient fitness became a liability.
Combined Impact on Performance
- Soldiers with faster 1.5-mile run times and optimal body mass (lean body composition) consistently performed better in the LM.
- For instance:
- Men with an average run time of 9.7 minutes and a body mass of 173.6 lbs were most successful.
- Women with run times around 10.9 minutes and a body mass of 144.8 lbs were likely to meet the LM pass standard.
- The best-performing individuals combined a strong aerobic base with efficient weight-to-strength ratios, allowing them to sustain high performance over the loaded march.
How Body Mass and Run Time Predict Loaded March Performance
The relationship between body mass and 1.5-mile run time in predicting 8-mile Loaded March (LM) performance is not always intuitive. Based on the study’s regression model, lighter soldiers with the same run time as heavier soldiers are predicted to perform better in the LM. Here’s why:
How the Model Works
The model assigns positive weight to aerobic fitness (run time) and negative weight to body mass in calculating a predictor score:
Principal Component = 0.666 × (Run Time Z-score) −0.666 × (Body Mass Z-score)
- Faster Run Time → More positive impact on LM performance.
- Higher Body Mass → More negative impact on LM performance.
Since body mass has a negative weight, higher mass predicts slower LM completion times, even if two individuals have the same aerobic fitness.
Study Performance Data
| Metric | Men | Women |
|---|---|---|
| 1.5-Mile Run Time (min) | 9.7 | 11.4 |
| Single Lift (kg) | 52 | 32 |
| Water Can Carry Distance (meters) | 302 | 157 |
| 8-Mile Loaded March Pass Rate (%) | 100% | 69% |
Takeaways
- Aerobic Fitness is King: The 1.5-mile run time is the strongest predictor of Loaded March success.
- Extra Weight is a Liability: Even if the extra weight is muscle, it adds to the total load carried, making movement less efficient.
- Leaner Soldiers Excel: Soldiers with high aerobic fitness and moderate body weight tend to perform the best.
Sources
- Coakley, S. L., Myers, S. D., Walker, E. F., Hale, B., Jackson, S., Greeves, J. P., Roberts, R., & Blacker, S. D. (2019). 1.5 Mile Run Time and Body Mass Predict 8-Mile Loaded March Performance, Irrespective of Sex. Journal of Science and Medicine in Sport, 22(3), 217-221.