Although the perfect training method will probably never exist, some are more or less suitable. To what extent isometric training and plyometric training in combination can be beneficial for training athletes, Konstantin Stamm explains.
We know from research that many athletic movements are characterized by very short ground contact times. For example, a sprinter's foot contact with the ground is about 0.1 s, while a one-legged takeoff in basketball or long jump takes little more than about twice that time, or about 0.14-0.17 s. Therefore, a distinction is also made between fast and slow strain shortening cycles. Movements are considered "fast" when the ground contact time is less than 250 ms. Movements of the fast strain shortening cycle include, besides the just mentioned continuous hurdle jumps or drop jumps of low height. The slow stretch shortening cycle includes, for example, complete changes of direction or jumps with pre-movement (countermovement jumps).
Fast force generation
The consequence of very short ground contact times, e.g. in sprinting, is that the muscles have only a very limited time to generate sufficient force. In order to make optimal use of this short time, the muscle fascicles must work close to the plateau of the force-length curve - and do so as far as possible over the entire period of ground contact - in other words, almost isometrically. The tendons make this possible by lengthening and shortening so that part of the total change in length of the muscle-tendon complex (MTU - Muscle-Tendon Unit) is taken over by them. At the same time, they store kinetic energy during their own lengthening and release it when they shorten (Stretch and Recoil).
Recent research by Keitaro Kubo - one of the leading researchers in this field - et al. has demonstrated this well. Sprinters differed from untrained subjects at high joint speeds in their ability to produce high active muscle stiffness. Thus, despite high speed, sprinters remain closer to the plateau of the force-length curve; they work isometrically. Optimal conditions, therefore, for generating force through muscle work despite short ground contact times. If this stiffness cannot be generated, eccentric lengthening of the muscles or fascicles occurs and optimal force development cannot be guaranteed.
Higher passive energy supply
In addition to the "active stiffness" of the musculature, one also speaks of the "passive stiffness", i.e. that of the tendons (tendon stiffness). It is easy to imagine this with the help of a rubber band that is pulled to length. The stiffer and thicker the rubber band is, the more energy is required to deform it. If you then let go of one side of the rubber band, it retracts to its original length. A stronger band springs back with more force - more force was needed to deform it - than a thinner one. For athletes, this means that a stronger tendon leads to higher passive energy supply in the stretch shortening cycle than a weaker one in a poorly trained athlete. Non-contractile elements of the musculature that store energy during stretching and release it during shortening should also be counted as part of that passive stiffness. These elements include the largest of all muscle proteins: titin. Although its role has not yet been fully clarified, it is considered certain that it plays an important role in terms of force production. Basically, the elastic components of the muscles, to which titin belongs, contribute about 70-75 percent to the concentric force increase in the stretch-shortening cycle.
Lower hysteresis in trained individuals
In addition to high stiffness - both active (musculature) and passive (tendons and non-contractile elements of the musculature) - good elasticity (under high load) and low hysteresis of the tendons support force production or athletic performance during fast movements. Hysteresis refers to the loss of energy a tendon exhibits between elongation and subsequent shortening. Research, of which there is still quite limited, has shown mixed results, but suggests less hysteresis in trained individuals compared to untrained ones. For example, a 2017 study showed that ski jumpers and runners had about a one-third reduction in hysteresis compared to the control group, while this was not true for water polo players. The results already point to the different sport-specific demands and training performed differently by the athletes.
"Elasticity" refers to the ability of tendons to elongate under high load. Thus, a tendon must be sufficiently stiff and elastic at the same time. This seems contradictory, but only at first glance. A tendon can be easily deformed, but at the same time have little elasticity. Such a tendon would suffer damage even with low force application and small range-of-motion. For optimal functioning of the muscle-tendon apparatus, the tendon must therefore be deformable (elastic) and strong (stiff) enough. Consequently, the question now remains: which training methods lead to the desired adaptations so that an athlete can optimally train his athletic abilities?
Isometric training for tendon function
It is not without reason that isometric training has gained increased popularity in recent years, as it is comparatively safe to perform and results in less stress on the joints. Likewise, maximal isometric contractions can recruit a higher number of muscle fibers than in eccentric and concentric ones. According to recent metastudies, adaptations in hypertrophy, maximal strength, and rate of maximal force development (RFD) can be achieved through the use of isometric training methods. However, not only physiological adaptations were registered, but also effects on KPIs (Key Performance Indicators) of top athletes, i.e. key performance indicators that are important for the athlete and serve as a basis for athletic success. For example, top cyclists were able to increase their maximum power and professional kayakers were able to take important seconds off their time trial duration by integrating high-intensity isometric training.
Ultimately, the training success or adaptation achieved is always determined by the programming of the training variables and the given situation (e.g., the athlete's condition, the time in the season, etc.).
Intensive isometric training
Of particular interest in the training of healthy athletes are high-intensity isometric training methods. Here, intensity refers to the amount of force the athlete exerts to move insurmountable resistance. In English, this form of isometric training is also known as "overcoming isometrics." According to recent studies, training at intensities greater than 90 percent results in multiple positive adaptations to mechanical (stiffness), morphological (tendon diameter), and material (elasticity) properties of tendons, which are two of the four desired adaptations. The insurmountable resistance can be realized by various equipment. For example, a tension belt or a wall against which the athlete must brace himself is sufficient. Of course, there is also the possibility of carrying out such training in the studio. In this case, for example, the athlete can use a barbell on his back (squat pattern) to push himself against pins from below and exert the desired amount of force.
M. triceps surae
An interesting and easy to implement way to quantify the intensity of training is presented by authors Radovanovic et. al (2021) in their article on training the triceps surae. By using a suitcase scale, the athlete receives direct feedback on the amount of force applied. Basically, it is a measuring station to determine isometric force. In the context of athletic training, this has been seen many times with the Isometric Mid-Thigh Pull exercise, which is in the context of athletes' jumping and sprinting ability. In 2018, the use of a low-cost crane scale versus a force plate was validated.
Plyometric training to increase active stiffness.
Another desirable adaptation - active muscular stiffness - can be achieved through plyometric training, but not through isometric training. This seems to be equally true for the elongation ability of tendons in high-speed movements. In this context, plyometric exercises must be adapted to those requirements of the elongation-shortening cycle to which the athlete is exposed in his sport. A sprinter is exposed to shorter strain shortening cycles in his discipline than, for example, a tennis player who has to perform complete changes of direction. Therefore, general statements regarding the design of plyometric training are difficult. In general, intensity and volume should be matched and factors such as training experience, timing in the competitive calendar, and injury history should be considered.
No consensus yet
Clear suggestions for implementing plyometric training depend on too many factors in training planning, and there is not yet agreement in the literature on quantifying plyometric training or its intensity. Therefore, the best thing coaches can do is to ensure that the athlete is subjected to a progressive increase in load during training. In this way, improvement in his athletic performance is possible, as is a reduction in the risk of injury. On the other hand, a too aggressive progression or a hasty increase in volume can lead to a negative adaptation or even worse to injuries.
The training methods presented produce a very good synergy when used together. While isometric training improves tendon function, plyometric training helps develop muscular stiffness and elongation capacity of tendons under high ballistic load. By themselves, neither training method can create the multiple adaptations athletes need in explosive sports. Only when they are combined do they develop their full effectiveness.
Conclusion
Many of the observations on the behavior of the muscle-tendon complex at high movement velocities-short stretch-shortening cycles with high joint velocities-are based on studies of the Achilles tendon, as other muscle-tendon complexes are more difficult to observe. Although it is possible that others behave similarly, it cannot be ruled out that the above statements apply primarily to this anatomical structure. Further research will be necessary to provide increased clarity in this regard.
Source and image source: Bodylife
Published on: 2 August 2023