Author(s): KOBAYASHI, Y., MAEO, S., KANEHISA, H., ISAKA, T., Institution: RITSUMEIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 2140

INTRODUCTION:
The bilateral deficit (BD) is the phenomenon that the force produced during simultaneous maximal contractions of both limbs is lower than the sum of the force produced by the left and right separately (Howard and Enoka, 1991). BD has been shown to be present in various, but not all, exercise tasks and is thought to influence training outcomes (Zeleznik et al., 2022). Thus, it is important to clarify whether BD occurs or not in exercises of interest. BD is reported to be greater in lower body than upper body exercises (Skarabot et al., 2016). However, there is large variability among studies targeting the lower body in the magnitude of BD, likely because different exercise tasks were chosen across studies. In addition, the magnitude of BD may be influenced by the posture even in the same exercise task (Magnus and Farthing., 2008). Thus, the purpose of this study was to investigate whether BD occurs in two commonly performed lower body resistance exercises, knee extension and flexion, with two postures for each exercise.
METHODS:
Ten untrained healthy young adults participated in this study. Bilateral and unilateral one-repetition maximum (1RM) were measured for both legs in two postures of Knee extension (seated and supine, hip flexion angle of 80 and 0 deg) and two postures of Knee flexion (seated and prone, hip flexion angle of 80 and 30 deg). In addition, we calculated the bilateral index (BI (%) = bilateral / (right unilateral + left unilateral) *100-100) to quantify the magnitude of BD.
RESULTS:
Bilateral force production was not significantly different from the sum of unilateral force production in two postures of knee extension (bilateral vs the sum of unilateral: seated, 133.2 ± 13.8 kg vs 131.1 ± 23.5 kg, P = 0.746, Cohen’s d = 0.106, BI = 3.46%; supine, 117.9 ± 19.1 kg vs 121.4 ± 21.8 kg, P = 0.155, Cohen’s d = 0.491, BI = -2.51%). On the other hand, bilateral force production was significantly lower than the sum of unilateral force production in two postures of knee flexion (seated, 92.1 ± 9.5 kg vs 110.8 ± 13.9 kg, P < 0.001, Cohen’s d = 1.648, BI = -16.50%; prone, 50.9 ± 7.8 kg vs 55.5 ± 9.5 kg, P < 0.001, Cohen’s d = 1.012, BI = -7.93%). In addition, BI was significantly lower (i.e. BD was greater) for seated knee flexion than the other three conditions (P ≤ 0.004) and for prone knee flexion than seated knee extension (P = 0.038).
CONCLUSION:
These results suggest that the bilateral deficit occurs in knee flexion, particularly when performed in the seated position, but not in knee extension regardless of the posture.

REFERENCES:
Howard & Enoka. J Appl Physiol 70:306-316, 1991.
Zeleznik et al. Sports (Basel). 2022;10(8):112.
Magnus & Farthing. Appl Phsiol Nutr Metab 2008;33:1132-1139.
Skarabot et al. Eur J Appl Physiol 2016;115(11-12):2057-2084.