(6) ELECTROMYOGRAPHICAL COMPARISON BETWEEN A DIGITAL WEIGHT SYSTEM AND TRADITIONAL FREE WEIGHTS

Purpose: The purpose of this study was to compare muscle activation during various exercises performed using a digital weight system and traditional free weights.

Methods: Healthy adults (26 ± 7 yrs.) participated in this study. Prior to the experimental conditions, a predicted one-repetition maximum (1RM) for each of the exercises was determined on the digital weight system (DWS). Visits 2-3 composed the experimental conditions in random order, traditional free weight (FREE), and DWS. During each experimental condition participants performed, in random order, 1 set of 9 repetitions of three separate exercises, bicep curls, skull crushers, and standing overhead shoulder press. Five minutes of rest was provided between each exercise to minimize the effect of fatigue. During the DWS condition, the digital weight system (Tonal Home Gym©, San Francisco, California) was set to dynamic load. During dynamic load, the load was 65% of 1RM at the transition from eccentric to concentric phases and the load increased during the concentric phase and decreased during the eccentric phase. The FREE condition was performed at 65% 1RM. During all exercises, surface electromyography (sEMG) were placed on the biceps brachii, triceps, and anterior deltoid in accordance with Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM) recommendations. Prior to each experimental condition participants performed two maximal voluntary isometric contractions (MVIC) for each muscle under investigation, for sEMG normalization. All sEMG was normalized to the respective MVIC and therefore all sEMG values are expressed as a percentage of MVIC. For each condition and exercise, repetitions 4, 5, and 6 were analyzed and averaged to provide a mean for each condition and exercise. T-test was utilized to assess differences.

Results: No differences in bicep brachii muscle activation were observed between the DWS and FREE during the bicep curl exercise (DWS = 36.39 ± 18.26 %MVIC, FREE = 27.68 ± 7.39 %MVIC, p = 0.35). Triceps muscle activation was not different between the DWS and FREE during the skull crusher exercise (DWS = 24.76 ± 4.32 %MVIC, FREE = 23.79 ± 9.19 %MVIC, p = 0.84). DWS and FREE resulted in similar muscle activation of the anterior deltoid during the standing overhead shoulder press (DWS = 41.34 ± 3.13 %MVIC, FREE = 36.98 ± 7.03 %MVIC, p = 0.24).

Conclusions: In the current investigation no differences in muscle activation were observed between free weight exercise and a digital weight system in the primary movers during the investigated exercises. PRACTICAL APPLICATIONS: Given the similar levels of muscle activation observed it appears that the digital weight system and free weights result in similar muscle stress despite the variable nature of the digital weight. These acute responses suggest that either the digital weight system or traditional free weights could provide an effective training stimulus.

Acknowledgements: None