Effect of differing intensities of fatiguing dynamic contractions on contrala-teral homologous muscle performance

The purpose of this study was to investigate different intensities of unilateral fatiguing dynamic quadriceps contractions on non-exercised,contralateral quadriceps performance. in a randomized crossover study design with 12 recreationally trained male (1.78 ± 0.05 m,84.5 ± 7.6 kg,30.0 ± 8.5 yrs) participants,maximal voluntary contraction (mvc) force,force developed in the first 100 ms (f100),and electromyography of the non-exercised contralateral knee extensors were measured before and after fatiguing protocols performed by ipsilateral knee extensors. non-exercised knee extensors’ endurance was also measured post-intervention. the fatigue protocols consisted of four sets of dynamic knee extensions each to task failure with 40% and 70% mvc on separate days. both the 40% (p = 0.009,effect size [es] = 0.72) and 70% (p = 0.001,es = 2.03) conditions exhibited 23.7% and 34.6% decreases in f100 respectively with the non-exercised contralateral knee extensors. a significant time effect (p = 0.002) demonstrated that both the 40% (and 70% (conditions exhibited 4.4% (es = 0.29) and 7.1% (es = 0.53) force decreases from pre-to post-intervention,respectively. however,the condition * time interaction only showed a trend (p = 0.09) with moderate (40%: es = 0.62) to large (70%: es = 0.82) effect sizes for decreased contralateral limb force compared with control session. the 40% (p = 0.09,es = 0.65) and 70% (p = 0.07,es = 0.79) protocols had a tendency to induce greater contralateral force variation during sustained sub-maximal isometric contraction compared with control. in conclusion,this study highlighted that unilateral lower limb fatigue induced by low intensity as well as high intensity dynamic knee extensions provided some evi-dence of crossover fatigue with the contralateral non-exercised limb. © journal of sports science and medicine.