Comparison of Muscle Activity Using Unstable Devices During a Forward Lunge

Abstract

Context: Unstable devices in various forms are used as therapeutic adjuncts for prevention or following an injury. A slip-over-the-shoe design with inflatable domes (STEPRIGHT® Stability Trainer) was developed to improve balance. It is unknown how this unstable device affects muscle activity during a closed-chain exercise such as the forward lunge. Objective: To compare muscle activity across 3 surfaces (STEPRIGHT®, Both Sides Up [BOSU®] Balance Trainer, and firm) during a forward lunge. Design: Within-subject, repeated measures. Setting: University physical therapy research laboratory. Participants: A total of 20 healthy, recreationally active subjects (23.4 [1.47] y, 172.7 [14.7] cm, 71.6 [16.8] kg). Intervention: Each subject performed 1 set of 10 repetitions of forward lunge exercise in random order with STEPRIGHT®, BOSU®, and firm surface. Main Outcome Measures: Surface electromyography data, normalized to maximum voluntary isometric contractions (%MVIC), was used to assess muscle activity on rectus femoris, vastus medialis oblique (VMO), biceps femoris, lateral gastrocnemius, fibularis longus, and tibialis anterior. Results: The repeated-measures analysis of variance determined that there was a significant effect for surface type. During the descent of the lunge, the STEPRIGHT® elicited higher rectus femoris (33% [27%] MVIC) compared with BOSU® (22% [14%] MVIC) and VMO (44% [15%] MVIC) on STEPRIGHT® compared with firm (38% [11%] MVIC) (P < .05). During the ascent of the lunge, the rectus femoris (38% [27%] MVIC) using STEPRIGHT® was higher than BOSU® (24% [16%] MVIC), and STEPRIGHT® elicited higher VMO (65% [20%] MVIC) versus BOSU® (56% [19%] MVIC) (P ≤ .01). The STEPRIGHT® for fibularis longus was higher (descent: 51% [20%] MVIC, ascent: 52% [22%] MVIC) than BOSU® (descent: 36% [15%] MVIC, ascent: 33% [16%] MVIC) or firm (descent: 33% [12%] MVIC, ascent: 35% [15%] MVIC) (P < .001). Conclusions: Clinicians may choose to use the STEPRIGHT® for strengthening VMO and fibularis longus muscles, as these were over 41% MVIC or any of the 3 surfaces for endurance training (<25% MVIC) for biceps femoris muscle. This information may be helpful in exercise dosage for forward lunges when using STEPRIGHT®, BOSU®, or a firm surface.