Power training adaptations -
In other words, if the body is presented with a demand rationally greater than it is accustomed to and enough recovery time is given to trained physiological systems, it adapts to the stressor by becoming stronger.
Until a few years ago, we believed that strength was determined mainly by the muscles' cross-sectional area CSA. As a result, weight training was used to increase "engine size" - that is, to produce muscular hypertrophy. However, though CSA is the single best predictor of an individual's strength Lamb , strength training research since the s and authors such as Zatsiorsky and Bompa have shifted the focus to the neural component of strength expression.
In fact, the primary role of the nervous system in strength expression was well documented by a review Broughton. Neural adaptations to strength training involve disinhibition of inhibitory mechanisms, as well as intra- and intermuscular coordination improvements. Disinhibition affects the following mechanisms:.
Adaptations in intramuscular coordination transfer well from one exercise to another, as long as the specific motor pattern is established intermuscular coordination.
For instance, the maximum voluntary recruitment of motor units developed through maximum strength training can be transferred to a sport-specific exercise skill as long as its technique is known by the athlete.
The objective of maximum strength macrocycles is to improve motor unit recruitment of the prime movers, whereas power macrocycles work mainly on rate coding. Contrary to popular belief, these two aspects of intramuscular coordination - recruitment and rate coding - play greater determinant roles than synchronization does in muscular force production.
Intermuscular coordination, on the other hand, is the capacity of the nervous system to coordinate the "rings" of the kinetic chain, thus making the gesture more efficient. With time, as the nervous system learns the gesture, fewer motor units get activated by the same weight, which leaves more motor units available for activation by higher weights see figure 2.
Therefore, to increase the weight lifted in a given exercise over the long term, intermuscular coordination training technique training is the key. Nevertheless, intermuscular coordination is very exercise specific, so its transfer to other exercises including sport-specific ones is very limited.
Even so, it remains the base for the athlete's general strength development. Over time, strength training for intermuscular coordination reduces the motor unit activation necessary to lift the same load, thus leaving more motor units available for higher loads.
Despite the fact that the hypertrophic response to training is immediate Ploutz, et al. These proteins, which represent the specific adaptive response to the imposed training, stabilize the achieved neural adaptations.
This is the way to read the famous study by Moritani and deVries see figure 2. Therefore, to increase strength over time, one must keep training the factors discussed here.
This is particularly true of intermuscular coordination, which allows load increase in the midterm and the long term on the basis of ever-increasing system efficiency, as well as specific hypertrophy.
Figure 7. Figure 8. Therefore, we collapsed across torque and utilized an ANCOVA model to analyze between group differences at Week 3 and Week 6 and one-way ANOVAs to investigate the change in VA across time within groups Figures 10C,D.
Because we were primarily concerned with the between group changes across time, we further evaluated the time × group interaction by collapsing across torque and utilizing an ANCOVA model to analyze between group differences at Week 3 and Week 6 and one-way ANOVAs to investigate the change in EMG QAMP across time within groups Figures 11C,D.
Specifically, 1RM and MVIC strength increased from Baseline to Week 6 by In the present study, muscle thickness increased by 6. These data add to the growing body of literature that has demonstrated comparable hypertrophic adaptations in response to high- vs.
low-load resistance training Mitchell et al. Hypertrophy has historically been thought to be minimal during the initial stages of resistance training Moritani and deVries, ; Sale, ; Gabriel et al.
Yet, several recent studies Seynnes et al. The present findings supported previous studies Seynnes et al. Damas et al. The authors Damas et al. Echo intensity would be expected to increase in the presence of muscle damage Radaelli et al.
Therefore, although these factors cannot be completely ruled out, the echo intensity measurements in the present study, as suggested by Damas et al. Ultrasound echo intensity has also been used as a surrogate of muscle quality Pillen et al.
For example, Pillen et al. Hill and Millan and Nieman et al. Although, several previous studies have demonstrated decreases in echo intensity following chronic resistance training Pinto et al. Resistance training is known to enhance intramuscular glycogen concentrations MacDougall et al.
When muscle glycogen and water content increase, ultrasound images become hypoechoic, resulting in lower echo intensity values. Incidentally, increased intramuscular water content may increase muscle cross sectional area as measured by MRI Kristiansen et al.
Although, it is also possible that glycogen and water concentrations influence ultrasound measures of muscle thickness, there are insufficient data in the present study to test this hypothesis. Future studies are needed to examine the impacts of muscle glycogen and intramuscular water on MRI Kristiansen et al.
Maximal isometric e. Figure 9. Figure Voluntary activation during MVIC increased 2. Furthermore, the 1. It has been described that large increases in synaptic input e. To illustrate the functional significance of the observed differences in VA, we applied a formula in Figure 6 that was described by Fowles et al.
This formula extrapolates the maximal torque generating capacity of a muscle from measures of MVIC and VA. Although, criticized Kooistra et al. This difference is may be due to a greater augmentation of neural drive Aagaard et al.
Traditionally, training-induced increases in EMG amplitude have been interpreted as increases in neural drive to the muscle Komi et al. We also examined VA and EMG QAMP during submaximal torque production at the same absolute levels of torque.
There was a These decreases were most apparent at high contraction intensities i. Furthermore, VA was lower across all submaximal torques at Weeks 3 and 6 in the 80 vs. A decrease in VA at submaximal torque levels suggests a reduced neural cost i. The changes in EMG QAMP across submaximal isometric torque observed in the present study were similar to those observed for VA.
Visual inspection of the EMG QAMP vs. torque relationships Figure 11A suggests decreases in EMG QAMP at high contraction intensities i. Our VA and EMG QAMP data during submaximal torque production may also support the findings of Falvo et al. The unique contributions of this study were the robust measurements VA and EMG QAMP during maximal and submaximal torque levels used to elucidate any potential underlying neural factors.
NJ was a substantial contributor to study concept and design, carried out data acquisition, analysis, and interpretation, and was the primary author. AM, EH, CS, and KC helped carry out data acquisition. TH contributed to study design and manuscript revision.
JC was the primary manuscript reviser and a substantial contributor to study concept, study design, and interpretation. All authors approved the final version of this manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors would like to acknowledge Brianna McKay and Alegra Mendez for their help with data acquisition. Aagaard, P. A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in muscle architecture.
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