Relationship of Isometric Peak Torque and Rate of Torque Development to Single Leg Hop Performance

Abstract

The use of isometric strength testing via portable fixed dynamometry (PFD) has increased in the field of sports medicine and while found to be reliable, little is known of its association to functional performance. PURPOSE: To assess the association of isometric peak torque (PT) and rate of torque development (RTD) to a single leg hop for distance (SLHD) task. METHODS: 36 NCAA Division I female soccer athletes (19.4±1 years, 166.4±5.1 cm, and 62.1± 5.3 kg) were recruited. Subject participation was required for one session. Subjects performed 3 trials of a SLHD task followed by an isometric knee flexor (KF) and extensor (KE) strength assessment. Subjects performed 3 max isometric contractions, 5 s in duration, separated by a 60 s rest period. Measures of interest were: single leg hop (SLH) distance [cm], SLH work performed in joules (work = subject weight [N] × distance hopped [m]), isometric PT [Nm], normalized isometric PT (%T = PT [Nm]/(weight [N] × height [m]), and isometric RTD [Nm/s] at 4 time intervals (0-30, 0-50, 0-100, and 0-200 ms). Isometric data were collected with a PFD sampled at 1000Hz and filtered using a low pass 4th order Butterworth filter with a cut-off frequency of 50Hz. Separate Pearson's Product-Moment Correlations were performed and the coefficients of determination calculated. The scale set forth by Hopkins (2002) was used to interpret the correlation coefficients: trivial (0.0), small (0.1), moderate (0.3), strong (0.5), very strong (0.7), nearly perfect (0.9), and perfect (1.0). RESULTS: All isometric PT and %T measures displayed a trivial to small positive (r =.01 to.24) correlation to SLH distance and work performed, except for KF %T that displayed a trivial inverse relationship (r = -.01) to SLH work. RTD to SLH distance displayed a small inverse relationship (r = -.15 to -.17), while RTD to SLH work performed displayed a trivial to small positive correlation (r =.07 to.14). The shared variance for isometric PT, %T, and RTD to SLH distance and work performed ranged from 0 to 6%. CONCLUSION: These findings suggest that isometric PT, %T, or RTD assessed at the KFs and KEs are not indicative of SLH distance or work performed. This may underscore the need to assess the muscular function of the lower limb not only in isolation (i.e. single joint measures), but also in a more functional and integrated multi-joint manner.