Bobbert, M. F., & Van Soest, A. J. (1994). Effects of muscle strengthening on vertical jump height: a simulation study. Medicine and Science in Sports and Exercise, 26, 1012-1020.

"Although a body of knowledge based on experience is very valuable, it still remains the task of investigators to substantiate training methods scientifically. The least scientists can do is offer practitioners a theoretical framework, from within which they can explain why some training programs or exercises have been more successful than others." (p. 1012)

The relative importance of control (learned skill) and various properties of the musculoskeletal system will vary with the particular type of activity in which the athlete is engaged. Vertical jumping depends primarily on control (skill) and muscle strength. In reply to the question on which factors a training program should focus to improve jump height, most coaches will say that the answer depends on the athlete's level of skill. They feel that in a novice athlete, supposed to have suboptimal control/skill, one can choose to try and improve either control or muscle strength. In an elite athlete, they will say, control is likely already to be optimal, so the focus in training should be on muscle strength. Consequently, to improve jumping height in expert volleyball players training aimed at increasing strength is advocated. Although in practice substantial gains in muscle strength may be achieved relatively easily, the corresponding effects on jump height are often quite inconclusive.

The adjustment of skill to changes in the physical properties of the strengthened muscle would be a critical factor to derive beneficial training effects from auxiliary training. Actual jumping achievement depends crucially on precise "timing" of muscle actions, that is, the skill of smooth coordination.

"If muscles are strengthened while control remains unchanged, jump height decreases rather than increases" (p. 1017). When control is not optimal, takeoff occurs prematurely and/or much muscular work is transformed into rotational energy segments at takeoff, so that the work is used less effectively. This implies that skill is paramount for jumping performance. Tuning control to system properties is a crucial step in maximizing vertical jump height (p. 1018). This supports the concept of having non-specific strength optimized prior to specific skill development.

The process of acquiring control skill is very time-consuming, involving weeks, months, or even years. Thus, when developing strength, it should be done at the same rate at which skill can be expected to change if it is done concurrently. For explosive actions, such as jumping, the learning of the skill relies heavily on pre-programmed muscle stimulation patterns (movement maps). Optimizing control takes at least several weeks of concentrated practice.

Muscle strength determines the maximal jump height that can be reached but actual performance relies crucially on the tuning of control to muscle properties. Muscle training exercises should be accompanied by exercises in which the athletes may practice with their changed muscle properties. Otherwise, athletes will not be able to adjust their control to benefit fully from the muscular improvements. Repetition of movement in which achievement is to be improved or, more precisely, repeatedly solving the task in which achievement is to be improved, seems indicated. Failure to do so may render training ineffective or even detrimental. Too strong an emphasis on muscle training exercises may be the reason for many failures to benefit from extra auxiliary training.

The critical feature in this consideration is the opportunity to practice the skill/control. In "simple" exercises like a vertical jump, the commonalty of the skill with leg extension in squats, squat jumps, and leg raises is quite high. Transfer of training effects could be expected. However, in a very complex and unnatural action such as swimming or kayak paddling, transfer may not be so easy. What would happen to a technique if only some of the many muscles involved were strengthened, or if all were strengthened but some more than others, is anyone's guess. However, it could be anticipated that dysfunctional movement characteristics (e.g., out of balance, asymmetrical actions, disruptions in movement smoothness) would result causing performance to be affected detrimentally.

Consequently, dedicated strength training of less than a carefully planned, and obviously individual nature, could be quite detrimental to an athlete's improvement. As long as skill improvements and analysis are emphasized, there is less likelihood that strength training will be counterproductive. However, if skill emphases remain at the same level as when no strength training was being conducted, it is likely that counter-productivity will be high. That counter-productivity will be increased in proportion to the complexity of the performance skill and the intended standard of performance.

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