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The Physiological Characteristics of Strength

Wednesday, January 20, 2016

The Physiological Characteristics of Strength

Strength may be defined as the neuromuscular capability to overcome an external and internal resistance. The maximum strength that an athlete can produce depends upon the biomechanical characteristics of a movement (i.e., leverage, the degree to which larger muscle groups may be involved) and the magnitude of contraction of the muscles involved. In addition, maximum strength is also a function of the intensity of an impulse (which dictates the number of motor units involved) and its frequency. According to Zatsyorski (1968) the number of impulses per second, may be elevated from 5-6 at rest up to 50 during the lift of a maximum load.

Following a strength training program a muscle enlarges itself (Morpurgo, 1897), or hypertrophies as a result of the following factors:
  1. the number of myofibrils (the slender threads of a muscle fiber) per muscle Tiber increases (hypertrophy),
  2. an increased capillary density per muscle fiber,
  3. an increased amount of protein,
  4. and an increased total number of muscle fibers.
All these occurrences lead to the general increase in a muscle's cross-sectional area. (Golberg et al., 1975; McDongall et at 1976. 1977. and 1979; Costill et al. 1979, Gregory, 1981; and Fox et al, 1989).
Zatsyorski (1968) considers that strength magnitude is a function of the following three factors:
  1. Intermuscular co-ordination, or the interaction of various muscular groups during performance. In a physical activity which requires strength there has to be an adequate co-ordination between the muscle groups which take part in the action. Often the muscles are involved in a certain sequence. For instance in clean and jerk (weight lifting), at the start and during the early part of the lift the trapezius muscle has to be relaxed. This muscle, however, should take part in the jerking phase. Very often though, even some elite athletes contract the trapezius from the beginning of the lift. This lack of co-ordination results in an alteration of the technical pattern of the lift, and consequently in an ineffective performance. Similarly, in sprinting events often the contraction of shoulder muscles has a negative effect upon the sprinter's performance. Therefore, it seems that the consequence of inadequate intermuscular co-ordination is a performance below one's potential, and both the coach and athlete should pay attention to it. Relaxation techniques seem to lead to an improvement in the coordination of muscular contractions.
  2. Intramuscular co-ordination; an athlete's force output depends also on the neuromuscular, units which simultaneously take part in the task. According to Baroga (1978) if during an arm curl the muscle biceps brachii has a maximum force output of 25 kg, electrical stimulation of the same muscle may result in an elevation of the muscle's force capacity by 10 kg. It is therefore apparent that the athlete often is not capable of involving all of the muscle fibers in any particular activity. This phenomenon is called by Kuznetsov (1975) the "force deficit" and may be improved by the employment of maximum load or other training methods (forthcoming in this chapter) which result in the recruitment of more neuromuscular units. 
  3. The force with which the muscle reacts to a nervous impulse. A muscle reacts to a training stimulus with only about 30% of its potential (Kuznetsov, 1975). The employment in training of the same methods or loads only leads to a proportional training adaptation. In order to elevate or bring about a superior threshold of adaptation higher intensity stimuli have to be used since maximum stimuli results in maximum effect. Therefore, one of the consequences of a systematic training is the progressive improvement of the nervous impulses synchronization, and the intensive activity of the antagonistic muscle (a muscle that acts in opposition to the action of another muscle) with the agonistic muscle (prime mover). A training program will also enable muscle fiber groups to alternate so that when one group of muscle fibers exhaust, another group will start to contract, thus resulting in strength improvement
It should be noted that the ability of an athlete to exert force is also dependent upon the angle of .the joint Research performed in this area has yielded conflicting results. While .some findings suggest that maximum strength is achieved when the joints are in full extension, or very close to it (Hunsicker, 1955; Eikins et al. 1957; Zatsyorski, 1968 etc) others reported higher muscular efficiency when the joint is flexed 90-100 degrees. As Logan and McKinney (1973) put it, a muscle must be placed at its longest length in order to exert its greatest force. However, the muscle is contracting in the direct fine of movement when the joint is flexed at 90° and is thus working at a greater mechanical efficiency. In fig. 103 (A) below, contractions start from a more open angle (arrow #2). In figure 103 (B), muscle contractions start from a more acute angle (arrow #3). It seems safe to say that the athlete can produce more force from an open angle joint than he/she could if the same joint was acute.
103.   Joint angle and muscle efficiency.