Running Performance: Is Smaller Better?

Body composition impacts many aspects of athletic performance. A new study investigates its relation to respiratory compensation point, or RCP.

Bodyweight and body composition are critical factors in most sports. Compare marathon runners to football linemen, for example. It’s no coincidence that they are dramatically different in size, muscularity, and body fat. This difference in size affects their performance. A recent study in the Journal of Strength and Conditioning Research compared respiratory compensation point (RCP) in participants with varying body composition. RCP is the point at which there is no longer a balance between the production of acid and the body’s ability to eliminate the acid. At this point, numerous metabolic changes occur and endurance takes a nosedive.

Normally, the body buffers acid through a few chemical channels, one of which is simply by breathing. Exhaling all by itself can actually reduce the acidity of the blood. When you first begin breathing harder during exercise, it’s because your muscles need more oxygen. Once exercise becomes intense enough you reach the RCP, and breathing speeds up in an attempt to further reduce acid. Hyperventilation during vigorous exercise is actually largely caused by acidosis, or too much acid, than by a greater need for oxygen.

It’s been long known in distance running that being small is an advantage. Because your body is the resistance when running, having lower resistance equates to better performance. In this study, the researchers theorized that lower bodyweight also meant a higher RCP. It was the first study of its kind, controlling the body composition pretty strictly in varied athletes, none of whom were overweight.

The researchers in the study compared the RCP of three difference groups: a control group, a group with higher body fat than the control, and a group with higher lean mass than the control. Here’s how the the three groups compared to each other:

  • The higher-lean mass group and higher-body fat group each had higher body mass total on average than the control group.
  • The lean-mass group was a little bigger than the high-fat group.
  • The lean-mass group averaged about 22lbs heavier than the control.
  • The lean-mass group had about as much body fat as the control group.
  • The high-fat group had about as much lean mass as the control group.

In the testing, the control group was faster and lasted longer in a treadmill test before reaching their RCP, at about 6.6 miles per hour (mph). Compare this to 5.8 mph for the high fat group and 5.9 mph for the high lean mass group. The control also lasted about two minutes longer than the lean mass group and had a heart rate of over ten beats per minute more than the lean mass group. When considered in the context of any sport or activity, these are huge differences.

Based on the results, it’s clear that muscularity helps endurance to a degree in similarly-sized athletes. However, total body size modulates endurance performance the most in sports where you are on your feet anyway, such as running.

Keep in mind that sports have varied needs. When a sport has a high aerobic component (basically any sport that lasts longer than, say, a minute), bodyweight is a major factor. Coaches should consider how light an athlete could be with just enough muscle to meet the demands of the sport so as to maximize endurance. In sports where the physical dimensions of the athlete are highly specific, such as basketball or weight-classed sports like MMA, appropriately balanced body composition needs to be addressed for the success of an athlete.


1. Marcin Maciejczyk, et. al., “Effect Of Body Composition On Respiratory Compensation Point During An Incremental Test,Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000347

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