Page 102 - JSOM Spring 2023

FIGURE 3 Funnel Plot of Studies Comparing Risk of Injury in
Healthy Weight to Underweight.
FIGURE 4 Forest Plot of Studies Comparing Risk of Injury in
Healthy Weight to Overweight.
FIGURE 5 Funnel Plot of Studies Comparing Risk of Injury in
Healthy Weight to Overweight.
FIGURE 6 Forest Plot of Studies Comparing Risk of Injury in
Healthy Weight to Obese.
100 | JSOM Volume 23, Edition 1 / Spring 2023
FIGURE 7 Funnel Plot of Studies Comparing Risk of Injury in
Healthy Weight to Obese.
As the introduction notes, relationship between BMI and in-
jury is likely complex because high BMI can be due to higher
body fat or higher fat-free mass (mostly bone and muscle).
The higher injury risk among underweight individuals may
reflect a paucity of either fat or fat-free mass. Low BMI may
render SMs more susceptible to injury because they may lack
the muscle mass or strength in the supportive structures (liga-
ments, bones) required to perform certain occupational phys-
ical tasks and/or they may overexert or overuse the available
muscle mass or supportive structures. Also, military clothing
and equipment may not be adequately sized to smaller body
dimensions. The proportion of underweight individuals in US
military samples in this review was small, ranging from 1.3%
to 4.3%. 55,57,65–67 Although the US military designs clothing
and equipment to account for the anthropometric differences
among individuals and regularly updates anthropometric
data, 69–71 some small individuals may be disadvantaged by
certain types of equipment that is not well tailored to their
more extreme body dimensions. These “smaller” individuals
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may be using military clothing and equipment (load-bearing
equipment, packs, weapon systems) that are uncomfortable
and produce repetitive stress on particular body parts, thereby
affecting injury risk directly or through discomfort affecting
attention and situational awareness.
Overweight individuals had only marginally higher injury risk
than healthy weight individuals, although the risk for obese in-
dividuals was similar (although somewhat lower) than that of
underweight individuals. If high BMI reflects a larger percent-
age of body fat relative to height, injury risk might be increased,
owing to the additional fat burden increasing the intensity of
physical activity, 73–75 thereby leading to more rapid fatigue.
The additional fat could impose additional repetitive stress on
the musculoskeletal system, owing to greater weight relative to
height. Studies have also shown that as body weight increases,
postural stability decreases. 76,77 Thus, excess body weight may
cause awkward movements that increase injury risk through
repetitive stress or acute events (i.e., falls, stumbles). Weight
loss improves balance control suggesting a causal relation-
78
ship between excess weight and postural stability.
In summary, this meta-analysis suggests that, compared
with normal weight SMs, those who are underweight, over-
weight, or obese have a higher risk of injury than those of
healthy weight. The higher injury risk was similar for those
underweight and those obese when compared with healthy
weight SMs. As a matter of prevention, it might be prudent
to remain in the healthy-weight BMI category, but we could