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.