What Predicts Whether You'll Finish a Long Ruck? Muscle Mass and Aerobic Fitness
- Alastair Hunt
- Jul 29
- 3 min read
Updated: Jul 30
Researchers set out to identify what actually determines success on a demanding, long-duration load carriage task. They studied 65 Reserve Officers' Training Corps cadets completing a 12 mile (19.3km) foot march carrying a 15.9kg (35lb) rucksack, against the US Army's 3 hour completion standard. The study measured body composition, Army Combat Fitness Test (ACFT) scores, and vertical jump power, then compared those who finished within the time standard against those who didn't.
As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment. Links to all studies / resources at bottom of page.
What They Found
Cadets who met the 3 hour standard had lower body fat percentage, more fat-free mass (lean muscle), higher overall ACFT scores, and better jump power than those who fell short.
When the researchers crunched the numbers further, two factors stood out as genuinely predictive: every one point increase in ACFT score raised the odds of finishing on time by 6.1%, and every 1 kg increase in fat-free mass raised those odds by 24%.
When they broke the ACFT down event by event, only the 2 mile (3.2km) run remained a significant predictor, with each point improvement boosting finishing odds by 9%.
What This Means for Us
This study offers a genuinely useful and specific training insight for anyone preparing for a long ruck event, not just a repeat of "get fit." The standout finding is fat-free mass. Building lean muscle appears to matter more than almost anything else measured here, more than general jump power, more than most individual fitness test components.
If you're training for a long ruck, dedicated strength training aimed at building muscle, not just losing weight, should be a core part of your programme.
The second clear signal is aerobic capacity, specifically reflected in 2 mile run performance. Despite rucking being a loaded, muscular-endurance task, straightforward running fitness was the one ACFT event that predicted success on its own. This suggests your engine matters just as much as your muscle when the march stretches past three hours.
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Final Thoughts
Together, these findings point to a fairly clean training prescription for anyone with a long ruck event on the calendar:
Build lean muscle mass through resistance training
Build your aerobic base through running or similar cardio work
Neither alone appears to be enough. It's a helpful, evidence-backed argument against training ruck fitness in isolation and skipping the gym or the run.
Wherever you are: train safe and enjoy the process!
Alastair
Studies & Resources
Sax van der Weyden M, Merrigan JJ, Martin J. Long Duration Load Carriage Performance Is Associated With Army Combat Fitness Test Scores and Fat-Free Mass. J Strength Cond Res. 2024 Nov 1;38(11):1959-1966. doi: 10.1519/JSC.0000000000004903. Epub 2024 Sep 17. PMID: 39454191.
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