Reliability of lower quarter physical performance measures in healthy service members

Measures of endurance, flexibility, strength, and power may be of value in predicting injury risk, but application to the military setting has been limited. The purpose of this study was to assess the reliability and precision of lower quarter physical performance measures among novice raters.

Sixty-four (53 male, 11 female) healthy active duty Soldiers (aged 25.2±3.8 years, 25.1±3.1 kg/m²) were recruited while in training at Fort Sam Houston, Texas. Subjects completed 13 lower quarter physical performance measures in a counterbalanced order. Measures included indicators of lumbopelvic endurance (trunk flexion, trunk extension, and trunk lateral flexion), lower extremity flexibility (gastrocnemius, soleus, iliotibial band, hamstring, and quadriceps), hip strength (hip external rotation, hip abduction), quality of movement (lateral step down), and lower extremity power (timed hop test and crossover hop test). Interrater test-retest reliability was assessed between baseline scores and those obtained 48 hours later using intraclass correlation coefficients (ICC) and standard errors of measurements (SEM).

Measures of lumbopelvic endurance had ICC(2,1) values ranging from 0.77 to 0.79 with SEM ranging from 18.3 to 24.5 seconds. Measures of flexibility had ICC(2,2) values ranging from 0.27 to 0.59 with SEM ranging from 4.1° to 9.9°. Measures of hip strength had ICC(2,3) values ranging from 0.61 to 0.82 with SEM ranging from 1.3 kg to 3.0 kg. Measures of power had ICC(2,3) values ranging from 0.78 to 0.93 with SEM values of 0.2 seconds and 27.4 cm.

The majority of measures assessed had adequate reliability in this sample of uniformed service members assessed by novice raters. The measures of strength and power had moderate to good reliability with small measurement error, indicating the possibility of these measures to detect change over time. Although the measures of lumbopelvic endurance had good reliability, they were associated with relatively large SEM values compared to the group mean, thus limiting the ability of these tests to detect change over time. The measures of flexibility had limited reliability which may be associated with a restriction in range of the underlying scores that could artificially underestimate reliability. These results can help inform which physical performance measures should be used in future research to assess injury prediction and human performance optimization among uniformed service members.