Background The in-line lunge (ILL) is used to determine muscle sling behavior and possible unilateral motor control asymmetries (UMCA). Though, its validity remains unclear.

Objective The aim of this analysis was to explore the relationship between UMCA and unilateral motor performance asymmetries (UMPA).

Design Correlational-study. To reduce bias of circadian effects we executed the testing sessions within a timeframe of ±1 h. A crossover design was used in order to avoid sequence effects.

Setting Collegiate athletes

Participants 54 healthy sportsmen were enrolled in the study, whereas 50 (43 men and 7 women; 22.3±1.6 yrs) completed the study.

Interventions The participants visited the laboratory twice. In session 1 they performed the FMS, followed by a warm-up including a treadmill run (10 min at 10 km/h) and 5 free split squats at 40% load of their bodyweight (FSS40). Thereafter, the participants performed 3 sets of 5 repetitions of the FSS40 intermitted by a recovery period of 1 minute. In session 2 the sportsmen underwent the same warm-up and FSS40 assessment, however the starting leg was switched. Kinetic data were recorded with a linear power encoder.

Main Outcome Measurements Correlational-Analysis. The criterion for a UMPA was determined by a weighted TEM based on Cohens d.

Results The relationship between UMCA and UMPA is low (r=0.2; p>0.05). In general, we identified 17 UMCAs and 13 UMPAs (8 weak, 4 moderate,1 strong). The ICCs of kinetic parameters were >0.9. TEMs were <7.5%.

Conclusions The data indicates that the association between UMCA and UMPA is low. Based on that evidence it seems that asymmetries are task specific. However, on the methodological level the scoring procedure could be a confounder for our result. Within a physiological context there are different factors that possibly explain the result, like different motor unit recruitment strategies, different muscle fibre distribution or connective tissue properties.