Test-Retest Variability and Reliability of Volitional and Nonvolitional Assessments of Muscle Endurance in Healthy Humans.

PURPOSE: Muscle endurance is commonly assessed using repeated or sustained volitional contractions, but measurement can be affected by subject cooperation and motivation. Nonvolitional techniques employing direct muscle stimulation may overcome the shortcomings associated with volitional techniques. We have therefore examined the variability and reliability of both volitional and nonvolitional techniques to assess quadriceps and handgrip endurance.

METHODS

Fourteen healthy participants (10 male, age 30 ± 7 yr, height 173.3 ± 9.2 cm, weight 67.0 ± 12 kg) completed measurements of strength and endurance on three occasions. Hand grip and quadriceps strength were determined from hand grip maximal voluntary contraction (HGMVC) and quadriceps maximal voluntary contraction (QMVC), respectively. Volitional hand grip endurance was determined as the time to task failure during a sustained contraction at 50% HGMVC. Volitional quadriceps endurance was assessed using repeated 5-s isometric contractions at 60% QMVC with 3 s rest until task failure. Nonvolitional quadriceps endurance was assessed using repetitive transcutaneous electrical stimulation (30 Hz, 250 ms on, 750 ms off for 180 s) at 30% QMVC. Endurance was taken as the time for the force to fall to 70% of the initial force. Variability was determined using the coefficient of variation, and reliability using intraclass correlation coefficient.

RESULTS

Volitional hand grip endurance demonstrated fair variability (20.5%) and good reliability (0.81). Volitional quadriceps endurance demonstrated good variability (15.2%) and good reliability (0.76) while nonvolitional quadriceps endurance demonstrated good variability (16.4%) and excellent reliability (0.92). Overall, HGMVC and QMVC demonstrated either good or very good variability and either good or excellent reliability.

CONCLUSIONS

Both volitional and nonvolitional measures of endurance in the hand and quadriceps muscles are reliable. Nonvolitional measures of muscle endurance may be helpful in cohorts unable to perform volitional maneuvers.