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: 2.08). 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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    • "When undertaking strength training to increase CNS activation of the targeted muscle, heavy loading and/or contractions performed to or near contraction failure (muscular exhaustion) are emphasized [10]. That is, CNS activation of the contracting muscle increases as contraction failure is approaching in healthy subjects [11], and strength training with heavy loading results in greater CNS activation of the exercising muscle compared low loading in healthy subjects [12]. Hence, both heavy loading and repetitions performed to contraction failure seem logic choices when strength training the quadriceps muscle to reduce arthrogenic inhibition following TKA. "
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    ABSTRACT: Loading and contraction failure (muscular exhaustion) are strength training variables known to influence neural activation of the exercising muscle in healthy subjects, which may help reduce neural inhibition of the quadriceps muscle following total knee arthroplasty (TKA). It is unknown how these exercise variables influence knee pain after TKA. To investigate the effect of loading and contraction failure on knee pain during strength training, shortly following TKA. Cross-sectional study. Consecutive sample of patients from the Copenhagen area, Denmark, receiving a TKA, between November 2012 and April 2013. Seventeen patients, no more than 3 weeks after their TKA. Main outcome measures: In a randomized order, the patients performed 1 set of 4 standardized knee extensions, using relative loads of 8, 14, and 20 repetition maximum (RM), and ended with 1 single set to contraction failure (14 RM load). The individual loadings (kilograms) were determined during a familiarization session >72 hours prior. The patients rated their knee pain during each repetition, using a numerical rating scale (0-10). Two patients were lost to follow up. Knee pain increased with increasing load (20 RM: 3.1±2.0 points, 14 RM: 3.5±1.8 points, 8 RM: 4.3±2.5 points, P = 0.006), and repetitions to contraction failure (10% failure: 3.2±1.9 points, 100% failure: 5.4±1.6 points, P<0.001). Resting knee pain 60 seconds after the final repetition (2.7±2.4 points) was not different from that recorded before strength training (2.7±1.8 points, P = 0.88). Both loading and repetitions performed to contraction failure during knee- extension strength-training, increased post-operative knee pain during strength training implemented shortly following TKA. However, only the increase in pain during repetitions to contraction failure exceeded that defined as clinically relevant, and was very short-lived. NCT01729520.
    PLoS ONE 03/2014; 9(3):e91107. DOI:10.1371/journal.pone.0091107 · 3.23 Impact Factor
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    ABSTRACT: Purpose: This study compared endurance and neuromuscular function after bouts of low-load (LL), high-load (HL), and LL blood flow-restricted (LL(BFR)) resistance exercise. Methods: Eight recreationally active male subjects completed three sets of dynamic knee extensions to volitional failure under three conditions: HL (70% peak torque), LL (20% peak torque), and LL(BFR) (20% peak torque with an occlusive cuff inflated to 180 mm Hg wrapped around the thigh). Before and immediately after exercise, isometric torque, central activation, electrically evoked torque, and muscle activation via surface EMG were measured. Results: Isometric torque and evoked torque decreased an average of 37% and 40%, respectively (P < 0.01) in all conditions after 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 with the LL and LL(BFR) 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 LL(BFR) conditions (P < 0.05). Conclusion: Although LL and LL(BFR) 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 · 3.98 Impact Factor
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    ABSTRACT: While elastic resistance training, targeting the upper body is effective for strength training, the effect of elastic resistance training on lower body muscle activity remains questionable. The purpose of this study was to evaluate the EMG-angle relationship of the quadriceps muscle during 10-RM knee-extensions performed with elastic tubing and an isotonic strength training machine. 7 women and 9 men aged 28-67 years (mean age 44 and 41 years, respectively) participated. Electromyographic (EMG) activity was recorded in 10 muscles during the concentric and eccentric contraction phase of a knee extension exercise performed with elastic tubing and in training machine and normalized to maximal voluntary isometric contraction (MVC) EMG (nEMG). Knee joint angle was measured during the exercises using electronic inclinometers (range of motion 0-90°). When comparing the machine and elastic resistance exercises there were no significant differences in peak EMG of the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) during the concentric contraction phase. However, during the eccentric phase, peak EMG was significantly higher (p<0.01) in RF and VM when performing knee extensions using the training machine. In VL and VM the EMG-angle pattern was different between the two training modalities (significant angle by exercise interaction). When using elastic resistance, the EMG-angle pattern peaked towards full knee extension (0°), whereas angle at peak EMG occurred closer to knee flexion position (90°) during the machine exercise. Perceived loading (Borg CR10) was similar during knee extensions performed with elastic tubing (5.7±0.6) compared with knee extensions performed in training machine (5.9±0.5). Knee extensions performed with elastic tubing induces similar high (>70% nEMG) quadriceps muscle activity during the concentric contraction phase, but slightly lower during the eccentric contraction phase, as knee extensions performed using an isotonic training machine. During the concentric contraction phase the two different conditions displayed reciprocal EMG-angle patterns during the range of motion. 5.
    12/2012; 7(6):606-16.
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