A comprehensive assessment of the cross-training effect in ankle dorsiflexors of healthy subjects: A randomized controlled study

Purpose: To investigate the cross-training effect, induced on ankle dorsiflexors (AD) by unilateral strength-training of the contralateral muscles, as transfer of peak torque (PT) and muscle work (MW) and their relative contributions to muscle performance.

Methods: Thirty healthy volunteers were randomly assigned to a training or control group. The trained group sustained a 4-week maximal isokinetic training of the stronger AD at 90 and 45°/s. At both angular velocities, PT, MW and MW/PT ratio were measured from both legs at baseline and after intervention (trained group) or no-intervention (controls). The familiarization/learning-effect was calculated and subtracted by PT and MW measures to obtain their net changes.

Results: Net PT increased in both legs (untrained: +27.5% at 90°/s and +17.9% at 45°/s; trained: +15% at 90°/s and +16.3% at 45°/s). Similarly, net MW increased in both the untrained (90°/s: +29.6%; 45°/s: +37%) and trained (90°/s: +23.4%; 45°/s: +18.3%) legs. PT and MW gains were larger in the untrained than trained AD (p<0.0005), with MW improving more than PT at 45°/s (p=0.04). The MW/PT ratio increased bilaterally only in the trained group (p<0.05), depending on the angular velocity.

Conclusions: The cross-training effect occurred in AD muscles in terms of both PT and MW, with MW adding valuable information to PT-analysis in describing muscle performance. Moreover, the MW/PT ratio allowed estimating the contributions of these parameters to muscle capability and may represent a novel index in isokinetic testing. The greater improvements in the untrained than trained limb raises interesting clinical implications in asymmetric conditions.