Does an Optimal Load Exist for Power Training?
MECHANICAL POWER CONTRIBUTES TO SUCCESS OF MOVEMENTS RANGING FROM ACTIVITIES OF DAILY LIVING TO SPORT TASKS. RESEARCHERS HAVE ATTEMPTED TO DETERMINE THE LOAD THAT MAXIMIZES MECHANICAL POWER. HOWEVER, DOES TRAINING AT THIS LOAD MAXIMIZE POWER ADAPTATIONS?
Loren Z.F. Chiu, MS, CSCSColumn EditorPower training using different loads causes specific changes to the force–velocity relationship that creates variability in the degree to which power output is improved. Several investigations have indicated that training with the load that maximizes power output is more effective at improving maximal power production and athletic performance than either lighter or heavier loading conditions (5, 7, 8). Kaneko et al. (7) examined 4 loading conditions; 0% of maximum isometric strength (Po), 30% Po (the load that maximized power output), 60% Po, and 100% Po. After 12 weeks of elbow flexor training, maximal power production was improved in the 30% Poo and 60% Po groups (26.1% versus 13.8% and 21.7%, respectively) and to a greater extent than the 100% Po group (22.4%). Thus, training with the load that maximized power output promoted all-round improvements to the force–velocity relationship (i.e., increased both maximum velocity and maximum force output), which translated into the most pronounced improvement maximal power output (7). Similarly, Häkkinen et al. (5) reported that explosive body weight jump training (load equivalent to approximately 30% of maximal dynamic strength—the load that maximizes power output in the jump squat [3]) resulted in a 21% increase in jump height after 6 months of training, whereas heavy resistance training (70–120% of 1RM in the squat) resulted in a significantly lower improvement of 7%. Although no doubt exists that increasing an athletes strength level through heavy resistance training directly impacts the ability to generate high power outputs, little evidence exists demonstrating that heavy resistance training is more effective at increasing maximum power than training with the load that maximizes power output. group significantly more so than both the 0% P
More recently, a hybrid theory of combined training using multiple loads has been hypothesized to improve adaptations after power training to a greater extent than single-load programs. Harris et al. (6) compared the effects of high-force (80–85% of 1RM), high-power (30% of Po), and combined (30% of Po and 80–85% of 1RM) lower body training programs. After 12 weeks of training, the high-force group displayed no change in vertical jump peak power or jump height whereas a significant training effect existed for both the high-power and combined groups. No differences existed between the adaptations of the high-power and combined groups, with very similar improvements observed in peak power (2.5% and 2.6%, respectively) and jump height (2.3 cm and 1.8 cm, respectively). Furthermore, an examination of the elbow flexors in untrained males revealed that combined training using 100% and 30% of Po resulted in a significantly greater improvement in maximum power than training with 0% and 30% of Po10). It is unclear whether similar results would be observed in trained athletes or if the combined training program was compared to single-load training at the load that maximized power output (30% of Po). It is important to note that no evidence of work performed by the different training groups was provided in either investigation and thus it is difficult to delineate whether the loading conditions or the magnitude of the stimulus applied contributed to these observations. Furthermore, the impact of combined training has yet to be examined in a trained subject population where the potential for increasing maximal strength is diminished. (19.5% versus 10.0% improvement, respectively) (
Although the exact physiological mechanisms underlying superior adaptations after training with a specific load remain unidentified, it is theorized that the load that maximizes power output provides a stimulus that elicits the greatest improvement in power production due to specific adaptations in neural activation patterns (5,7,8). Several investigations have observed increases in muscle activity to occur at the specific load and movement velocity used in training (5,8). This suggests an increase in neural drive through the selective recruitment of high threshold motor units, increased firing frequency, and/or synchronization of motor units. Because adaptations are most pronounced at the load used in training, the load that maximizes power output provides the best stimulus to elicit the physiological changes necessary to increase maximal power output. Changes in muscle fiber contractile properties have also been postulated to contribute to adaptations following power training however little evidence to this effect currently exists.
A major obstacle to the identification of an optimal load has been the variety of methodologies used to measure power output (2,4). As a consequence, large disparities in the optimal load have been reported leading to ambiguity surrounding the load-power relationship (1,9). Methods reliant solely on kinematic (e.g., linear position transducer [LPT]) or kinetic (e.g., force plate) data have limitations when used for the determination of power output in various movements (2). The combination of kinetic and kinematic equipment (i.e., force plate and LPT) should be used to obtain the most valid representation of muscle power generation during dynamic movements (2,4).
The current literature indicates the load that maximizes power output in a specific movement is the optimal training load to elicit improvements in maximal power output. This optimal load provides a stimulus that results in the greatest improvement in maximal power output due to velocity specific increases in neural drive. Although training with a combination of intensities may improve power output across a greater portion of the force–velocity relationship, the degree at which maximal power output is increased remains unclear. Further examination is necessary to elucidate if improvements to maximal power output and athletic performance differ between single-load and multiple-load training programs in which the total work performed in both programs is equivalent.
Prue Cormie, MS, CSCS
Edith Cowan University, Perth, Australia
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