The relationship between voluntary and electrically evoked muscle contractile properties in young women

Isokinetic dynamometry and neuromuscular electrical stimulation [NMES] are commonly used to assess muscle contractile function, but few studies have investigated the relationship between the two, particularly in women. Thirty young women (age 23 ± 5 y) therefore performed maximal knee extensions on an isokinetic dynamometer at angular velocities of 0.00-6.28 rad/s, after which NMES of the quadriceps was used to determine unpotentiated and potentiated twitch contractile properties as well as the torque-frequency relationship. Voluntary isometric peak torque was correlated with peak torque, absolute rate of torque development, and the absolute rate of relaxation during potentiated twitches (ie, r = 0.557, 0.585, and -0.650, P = 0.00786, 0.00411, and 0.000779, respectively). Voluntary isokinetic peak torques at 1.57 and 3.14 rad/s were also correlated with the potentiated absolute rate of torque development (ie, r = 0.597, P = 0.00309 and r = 0.551, P = 0.00849, respectively). No other significant correlations were found between voluntary and electrically evoked muscle contractile properties, including various measures of the torque-frequency relationship. 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.