Muscle activation strategies during strength training with heavy loading vs. repetitions to failure.

National Research Center for the Working Environment, Copenhagen, Denmark.
The Journal of Strength and Conditioning Research (Impact Factor: 1.86). 10/2011; 26(7):1897-903. DOI: 10.1519/JSC.0b013e318239c38e
Source: PubMed

ABSTRACT Going to failure, or not, has probably been one of the most debated issues during the history of strength training. However, few studies have directly compared the physiological effect of failure vs. nonfailure strength training. The purpose of this study was to evaluate muscle activation strategies with electromyography (EMG) during heavy repetitions vs. repetitions to failure with lighter resistance. Fifteen healthy untrained women performed a set with heavy loading (3 repetition maximum [RM]) and a set of repetitions to failure with lower resistance (∼15 RM) during lateral raise with elastic tubing. Electromyographic amplitude and median power frequency of specific shoulder and neck muscles were analyzed, and the BORG CR10 scale was used to rate perceived loading immediately after each set of exercise. During the failure set, normalized EMG was significantly lower during the first repetition and significantly higher during the latter repetitions compared with the heavy 3-RM set (p < 0.05). Normalized EMG for the examined muscles increased throughout the set to failure in a curvilinear fashion--e.g., for the trapezius from 86 to 124% maximal voluntary contraction (p < 0.001)--and reached a plateau during the final 3-5 repetitions before failure. Median power frequency for all examined muscles decreased throughout the set to failure in a linear fashion, indicating progressively increasing fatigue. In conclusion, going to complete failure during lateral raise is not necessary to recruit the entire motor unit pool in untrained women--i.e., muscle activity reached a plateau 3-5 repetitions from failure with an elastic resistance of approximately 15 RM. Furthermore, strengthening exercises performed with elastic tubing seem to be an efficient resistance exercise and a feasible and practical alternative to traditional resistance equipment.

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    ABSTRACT: PURPOSE: This study compared endurance and neuromuscular function after bouts of low-load (LL), high-load (HL) and low-load blood flow restricted (LLBFR) resistance exercise. METHODS: Eight recreationally active male subjects completed 3 sets of dynamic knee extensions to volitional failure under three conditions: HL (70% peak torque), LL (20% peak torque), and LLBFR (20% peak torque with an occlusive cuff inflated to 180 mmHg wrapped around the thigh). Before and immediately following exercise, isometric torque, central activation, electrically evoked torque and muscle activation via surface electromyography (EMG) were measured. RESULTS: Isometric torque and evoked torque decreased an average of 37% and 40%, respectively (P < 0.01) in all conditions following exercise. There were no differences in the toque decrements between the conditions (P>0.05). Percent central activation did not change after any condition (P = 0.09). Rate of torque development declined an average of 26% after all three conditions (P=0.003) and rate of half-relaxation time was depressed by 48% after the HL condition (P=0.004) only. EMG amplitude was greater in the HL condition at the beginning and end of exercise compared to the LL and LLBFR conditions (P=0.001). At the end of exercise, EMG amplitude rose 19% (P=0.02) and was not different among conditions (P>0.05). Subjects performed more repetitions during the LL and LLBFR conditions (P<0.05). CONCLUSION: Although LL and LLBFR resistance exercise to volitional failure exhibit lower levels of muscle activation than HL exercise, similar torque decrements occur after all bouts of resistance exercise and the muscle fatigue can be attributed to peripheral factors.
    Medicine and science in sports and exercise 08/2012; 45(1). DOI:10.1249/MSS.0b013e31826c6fa8 · 4.46 Impact Factor
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