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

•A crossed transfer of peak torque and work is reported in ankle dorsiflexor muscles.•Work increased more than peak torque, depending on the angular velocity employed.•Performance gains were significantly larger in the untrained than trained muscles.•Peak torque and work contribute in a different proportion to muscle strength.•Analysis of peak torque, work and their ratio allows a full assessment of strength.

PurposeTo 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.MethodsThirty 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.ResultsNet 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.ConclusionsThe 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.