The relationship between voluntary and involuntary muscle contractile properties in young women

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. PURPOSETo determine the relationship between voluntary isometric and isokinetic torque and torque during involuntary, electrically evoked contractions of the knee extensor muscles. METHODSThirty 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 {micro}s) 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. RESULTSVoluntary 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. CONCLUSIONAlthough 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. O_FIG O_LINKSMALLFIG WIDTH=191 HEIGHT=200 SRC="FIGDIR/small/24316419v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@8e14b7org.highwire.dtl.DTLVardef@1f22be7org.highwire.dtl.DTLVardef@2052deorg.highwire.dtl.DTLVardef@20a02d_HPS_FORMAT_FIGEXP M_FIG C_FIG