The Relationship Between Voluntary And Involuntary Muscle Contractile Properties In Young Women

Isokinetic dynamometry and electrical stimulation are two common approaches for quantifying muscle contractile properties. Surprisingly few studies, however, have investigated the relationship between such voluntary and involuntary testing procedures. PURPOSE: To examine correlations between voluntary isometric and isokinetic torque and torque during involuntary, electrically-evoked contractions of the knee extensor muscles. METHODS: Ten young women (age: 25 ± 7 y) performed maximal knee extensions on an isokinetic dynamometer at angular velocities of 0, 1.57, 3.14, 4.71, and 6.28 rad/s. Following this testing, electrical stimulation of the quadriceps (400 V, 200 μs) was used to determine unpotentiated and potentiated peak twitch torque (PTT), rate of torque development (RTD), and rate of relaxation. The quadriceps were also stimulated with 1 s trains at 1, 5, 10, 15, 20, 25, 30, 35, 40, 60, 80, and 100 Hz to determine the force-frequency relationship. RESULTS: Significant correlations (p ≤ 0.05) were found between voluntary torque at angular velocities of 1.57-4.71 rad/s and both unpotentiated and potentiated PTT (R = 0.70-0.78); however, no significant correlation was found at 0 or 6.28 rad/s. Significant correlations were also found between voluntary absolute RTD and both unpotentiated and potentiated absolute and relative RTD (R = 0.67-0.77). No significant correlations were found between voluntary exercise performance and various measures of the force-frequency relationship. CONCLUSION: Although there is some relationship between voluntary and involuntary measurements of muscle contractile function, such results are only moderately well-correlated at best. The two techniques should therefore be considered complimentary rather than interchangeable.