Effect of instability and resistance on unintentional squat-lifting kinetics.
BACKGROUND
Resistance training while using an instability-training device is known to increase activation of stabilizing muscle groups while decreasing the force generated by the prime movers during isometric contractions.


OBJECTIVE
To investigate differences in squat kinetics during dynamic resistance training in an increasingly unstable training environment.


METHODS
Fourteen active men participated in this study. In each testing session, each participant performed 3 repetitions of squats with a 10-repetition maximum (10-RM) resistance, 40% of their 10-RM resistance, and 20.45 kg. The 3 testing session consisted of standing on a stable floor, foam pads, or BOSU balls. All repetitions were recorded with an optical encoder to record barbell kinetics.


RESULTS
The transition from stable (floor) to very unstable (BOSU) resulted in high likelihoods (>75%) of clinically meaningful differences ranging from small to large (effect size [ES] 0.31-1.73) in factors relating to concentric kinetics, eccentric power, and squat depth, regardless of the resistance used for training. There were also likely differences at the heaviest resistance in peak concentric power (stable to foam: ES 2.06; foam to BOSU: ES 0.38), eccentric power (stable to foam: ES 1.88; foam to BOSU: ES 0.74), and squat depth (stable to foam: ES 0.50; foam to BOSU: ES 0.67).


CONCLUSIONS
Resistance training in an unstable environment at an intensity sufficient to elicit strength gains of the prime movers results in deleterious effects in concentric squat kinetics and squat technique. Such observations are particularly evident on very unstable platforms.
Drinkwater
Eric J
EJ
School of Human Movement Studies, Charles Sturt University, Bathurst, New South Wales, Australia.
Pritchett
Erica J
EJ
Behm
David G
DG
D000222:Adaptation, Physiological; D000328:Adult; D000704:Analysis of Variance; D006801:Humans; D007537:Isometric Contraction; D007866:Leg / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D055070:Resistance Training; D014891:Weight Lifting / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology