Comparison of bilateral and unilateral contractions between swimmers and nonathletes during leg press and hand grip exercises

The bilateral limb deficit (BLD) is defined as the reduction in force production during bilateral compared with summed unilateral contractions of homologous muscles. The underlying mechanism for the BLD has been elusive to determine. The purpose of this study was to examine the presence of the BLD during maximal isometric leg press and handgrip exercises in female swimmers (n = 9, mean age = 20.1 ± 1.3 years) and nonathletes (n = 9, mean age = 21.7 ± 1.3 years) to gain further insight into this phenomenon. Force and electromyography (EMG) measures were collected from participants under bilateral and unilateral conditions for handgrip and leg press exercises. Bilateral limb ratios (BLR) were calculated for swimmers (BLRS) and nonathletes (BLRNA). A deficit was found for swimmers and nonathletes in leg force (BLRS = 79.84% ± 13.09% and BLRNA = 81.44% ± 19.23%) and leg EMG (BLRS = 88.45% ± 15.41% and BLRNA = 94.66% ± 13.62%); however, no BLD was seen in hand force (BLRS = 98.30% ± 11.21% and BLRNA = 95.91% ± 11.04%) and hand EMG (BLRS = 102.42% ± 11.20% and BLRNA = 103.30% ± 16.50%). Furthermore, no significant differences were found between groups for leg force, leg EMG, hand force, and hand EMG. In conclusion, a BLD was detected for both groups during bilateral isometric leg press. This suggests that while the BLD may be affected by neural influences, there may other factors involved such as postural stability requirements to perform the exercise.