Isokinetic dynamometry and neuromuscular electrical stimulation (NMES) are two commonly used approaches for quantifying muscle contractile properties. Few studies, however, have investigated the relationship between such testing procedures, particularly in women.

PURPOSE To determine the relationship between voluntary isometric and isokinetic torque and torque during involuntary, electrically evoked contractions of the knee extensor muscles.

METHODS Thirty young women (age 23 ± 5 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, NMES of the quadriceps (400 V, 200 µs) was used to determine unpotentiated and potentiated twitch contractile properties. 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 torque-frequency relationship.

RESULTS Voluntary torques at 1.57 and 3.14 rad/s were significantly correlated (i.e., multiplicity-adjusted P≤0.01) with the rate of torque development during potentiated twitches (r = 0.60 and 0.55, respectively). No other significant correlations were found between voluntary and involuntary muscle contractile properties, including various measures of the torque-frequency relationship.

CONCLUSION Although there is some relationship between voluntary and NMES indices of muscle contractility, such results are only moderately well-correlated at best. The two techniques should therefore be considered complementary rather than interchangeable.

The authors have declared no competing interest.

Madison J. Fry was supported by an Undergraduate Research Opportunity Program grant from the Center for Teaching and Learning at Indiana University Indianapolis.

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Ethical approval was granted by the Human Studies Committee of Indiana University.

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