A GOOD REVIEW OF RESEARCH INTO STRENGTH
Morrissey, M. C., Harman, E. A., & Johnson, M. J. (1995). Resistance training modes: Specificity and effectiveness. Medicine and Science in Sports and Exercise, 27, 648-660.
Research on various types of resistance training and research findings were reviewed. The authors were prepared to offer opinions based on the strength of collective studies.
Isometric versus Concentric Training
Each kind of training produces the greatest improvement when strength tests used are similar to those of training. Most improvements are observed when the test routine matches the training routine. Exercise-type specificity is supported.
Improvement in functional (sporting) performance is the most practical criterion for comparing training effectiveness of various types of exercise, despite functional activities usually being more complex and employing additional capacities to the performance of the trained muscle groups. It appears that concentric training may be superior to static training for improving performance although more research needs to be conducted to conclusively define an answer.
Isometric versus Eccentric Training
It is unclear as to whether isometric training is superior to eccentric training in increasing isometric strength, with the majority of studies indicating no difference. One study has reported eccentric training superior for developing eccentric strength.
There are no reports comparing the effects of the two forms of training on functional strength.
Isometric versus Concentric/Eccentric (Dynamic) Training
Most analyses of static versus dynamic training involve the comparison of isometric exercise to weight training. Generally, isometric training improves isometric strength more than does dynamic training.
There is not such a clear distinction of specificity for dynamic training possibly because of the movement speeds used for testing and training. When dynamic exercises are performed slowly, the nature of the contractions at least approaches isometric form, particularly at the initiation and cessation of movements. This suggests that isometric training could influence slow moving performance. However, in studies where fast training and testing movements have been performed the evidence supports dynamic training over isometric training.
It is difficult to draw any conclusion about one form of resistance training being better than the other with regard to functional performance. A notable quote was: "dynamic training essentially increases the speed of movement against light loads, whereas isometric training essentially increases the speed of movement against high mechanical resistance." [Duchateau, J., & Hainaut, K. (1984). Isometric or dynamic training: Differential effects on mechanical properties of a human muscle. Journal of Applied Physiology, 56, 296-301.]
Concentric versus Eccentric Resistance Training
Upper-body research indicates that eccentric training is superior for developing eccentric strength but there is little evidence to support concentric training being better for developing concentric strength.
In the lower body the specificity of training type emerges. Eccentric trains eccentric and concentric trains concentric strength.
Eccentric strength is trained more specifically by eccentric training. However, this could be due to the fact that few eccentric movements are trained specifically and so such actions have a greater potential for improvement. On the other hand, concentric actions are frequently trained and have less room for improvement. That difference could account for the more dramatic effects in eccentric as opposed to concentric training studies.
Neither concentric nor eccentric training is superior for developing isometric strength.
The two normal mechanisms for strength improvement are classified as hypertrophic or neural. There is insufficient evidence to attribute one or both to observed changes. However, as in all strength training, early changes, being so large and quick to occur, are most probably due to neural reorganization of existing resources rather than through physical changes such as hypertrophy.
More research is needed to determine the relative advantages of concentric versus eccentric exercise for contributing to functional performance improvements.
Weight Training versus Isokinetic Exercise
". . there is a strong belief by clinicians who treat musculoskeletal injury that isokinetic devices offer unique advantages and may even be superior to weight training. However, no studies have been reported that prospectively compared these two types of training programs in musculoskeletal injury rehabilitation." (p. 652)
Most studies comparing weight and isokinetic training involve uninjured Ss.
The evidence tends to support exercise-type specificity regarding isokinetic exercise versus weight training. Ss improve more in the activities and form of activity in which they are trained.
There is a slight hint in the limited literature that isokinetic training might have an advantage over weight training for improving functional performance. However, much more research needs to be conducted before a definitive statement can be offered.
The question of whether resistance training at one contraction velocity affects performance only at that velocity or a broad range of velocities needs to be answered.
In velocity-specific studies in which testing and training were both isokinetic, and peak torque was the strength criterion, strength usually improved most at the velocity at which training occurred. Usually, there were diminishing strength increases at velocities above and below the training velocity.
Velocity-specific studies using power as the criterion variable have produced mixed and inconclusive results.
Velocity specificity does not appear to be a strong factor in eccentric training. However, that may be because eccentric activities are usually so poorly trained that any training, even non-specific training, will induce some performance improvements.
Some studies suggest faster exercises are preferable for improving the speed of fast sports-related body movements, but the sparse relevant data available are inconclusive. Static and dynamic exercises require learning how to generate high forces via neural stimulation of the muscle. Strength and conditioning programs that place all their expected success on muscle-only responses without considering the roles of the brain and central nervous system are likely to fail to achieve outcomes.
Range of Motion Specificity
For isometric training, strength gains are highest at the angle or position of training with some diminished benefits outside that specific location. For dynamic training, the range of motion employed is critical for strength changes are likely to be highest in the training range with benefits decreasing outside of that range.
The concept of specificity of training in resistance exercise is generally supported in the literature. Exercise-type specificity is amply supported. Greatest gains are demonstrated when testing is performed on the same activity that has been trained (i.e., specificity of training effects). Both range of motion and training velocity specificity have been largely supported.
Faster training speeds favor improving faster movements in athletic activities. This appears to be related to a preferential development of fast-twitch muscle fibers and a neural component involving learning rapid muscle contractions.
"Because static vs dynamic exercise-type specificity has been clearly demonstrated, one would expect to find clear evidence that dynamic exercise is better than static exercise for improving performance in dynamic functional activities. Surprisingly such evidence has not been strong. One of the reasons why static exercise is effective for improving dynamic performance is that both static and dynamic training produce similar hypertrophic effects. Also, both kinds of exercise require learning how to generate high forces via neural stimulation of the muscle. In addition, movements such as the vertical jump start from zero velocity. Thus even slow speed strength is critical for accelerating the body early in the movement." (p. 657)
The speed with which force is applied is more critical for development of the ability to exert force at high movement speeds than is the dynamic or static nature of the exercise movement. [See Behm, D. G., & Sale, D. G. (1993). Intended rather than actual movement velocity determines velocity-specific training response. Journal of Applied Physiology, 74, 359-368.]
Early indications are that concentric training is superior to eccentric training for developing functional performance.
Weight lifting and isokinetic training have been compared as to their effects on isometric strength and functional performance, isokinetic performance seeming to be superior. The difference may be related to the normally faster movement speeds and higher effort levels of isokinetic than weight training exercises.
Despite the fact that most auxiliary strength training involves dynamic free or stacked weights, most research has focused on isokinetic machines.
This is an excellent review of the research. It tangentially points out that there is not much hard evidence supporting strength training as a viable means for improving athletic (functional) performance. When most studies test on the activities which are trained, and improvements are shown, that may simply be an artifact of a training effect rather than a strength effect. Because arm-curl strength is improved through training does not mean that activities involving the arm will be improved in trained athletes although there may be some improvements in sedentary individuals.
The article was limited to the assessment of research on strength training parameters. It did not assess the value of strength training for effecting performance changes in highly-trained athletes in activities such as rowing ergometer performance, speed skating times, and throwing velocity. Published work in those domains has shown no training benefit from resistance training.
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