Force generation and neuromuscular activity in multi-joint isometric exercises: comparison between unilateral and bilateral stance

The purpose of the present study was to look at lower extremity force generation and neuromuscular activation by comparing isometric mid-thigh pull in the unilateral stance (IMTPUni) and bilateral stance (IMTPBi), and identifying the characteristics of IMTPUni. Fifteen male collegiate athletes (age: 20.60 ± 1.50 years, height: 1.74 ± 0.05 m, mass: 69.04 ± 4.23 kg) performed IMTPUni and IMTPBi as multi-joint isometric exercise. Ground reaction force (GRF) was measured to assess force generation during IMTP. Surface electromyography (EMG) was used to measure neuromuscular activation in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus, biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL), which were represented as average rectified values (ARVs). The EMG of the muscles during IMTPUni was normalized by IMTPBi to compare relative change among muscles. The co-contraction index (CI) during IMTPUni was also calculated by using normalized EMG. As a result, IMTPBi was significantly higher in BF than IMTPUni. However, in IMTPUni, although only one leg contributed to produce force, GRF of IMTPUni reached 80% of neuromuscular activity relative to IMTPBi. While the neuromuscular activation of Gmax, Gmed, BF, RF and VL was significantly higher proportionately in IMTPUni compared to IMTPBi, neuromuscular activation was even greater in Gmax and Gmed. The co-contraction index (CI) was increased in IMTPUni. The features of neuromuscular activation during IMTPUni were similar to the single leg squat and step-up exercise examined in previous studies due to the necessity to support the body with a single leg.