DIFFERENCES IN UNILATERAL CHEST PRESS KINEMATICS ON A STABLE VERSUS UNSTABLE SURFACE WHILE HOLDING 1 VERSUS 2 DUMBBELLS

The following study evaluated the effectiveness of the COR Bench, to determine if its unstable surface allows for both greater range of motion and greater tendency towards co-contraction, in comparison to a traditional flat bench. An initial session assessed the 19 participants’ (age, 22.364 ± 2.480 years; mass, 77.850 ± 18.328 kg; height, 1.787 ± 0.0923 m) current one- repetition maximum strength levels for the unilateral chest press. Four different conditions were used to test the kinematic variables such that each participant completed 5 repetitions of unilateral chest presses at 70% of their max with one and two dumbbells on both the COR Bench and traditional flat bench. Differences in ROM were evaluated by measuring an angular representation of the shoulder complex. Levels of co-contraction were determined by analyzing the middle trapezius EMG. The results indicate a significant difference in ROM between the conditions (p = .00); specifically, a greater ROM during the one dumbbell condition versus the two dumbbell condition on the COR and the flat benches (p = .002, 0.001 respectively); greater ROM with two dumbbells on the COR bench compared to the flat bench (p = .022). The middle trapezius EMG data showed a significant difference in co-contraction levels between conditions (p = .00); specifically, a greater co-contraction during the one dumbbell condition versus the two dumbbell condition on the COR and the flat benches (p = .001, 0.008 respectively); greater co- contraction with one dumbbell on the COR bench compared to the flat bench (p = .010). This lends support for the future use of the COR bench as a means for more efficient exercise through a full range of motion; however, it also suggests that more practice is necessary to master the movement on the bench to decrease co-contraction activity.