August 27, 2018
ECCENTRIC EXERCISES: STUDYING “VACCINES” FOR MUSCLES
One of the biggest problems that athletes face is muscle injury, especially in top-level competition. One of the muscle groups that is most sensitive to this type of injury is the hamstring, which is located in the back part of the leg and is used particularly during sprints.
To work on these muscles and prevent possible damage, it is important to train them using eccentric exercises, which generate tension through stretching. An example of this are “dead lift” exercises. However, intensive training can also cause muscle damage, so it is important to be vigilant in order to keep injury risk to an absolute minimum.
Recently, several members of the FC Barcelona medical team participated in a study which analyzed the individual variability of this damage and its follow-up through different diagnostic techniques. This study was published in the journal Frontiers in Physiology.
Eccentric exercises: controlled “vaccines”
“Eccentric exercises are a good strategy for injury prevention,” states Gerard Carmona, researcher at the FC Barcelona Performance Area and the Escuela Superior de Ciencias de la Salud Tecno Campus, and the lead author of this article. When these exercises are carried out, “they trigger adaptation processes that protect the muscle: they work as a kind of vaccine.”
However, it is advisable to monitor the effects of this training, because depending on the athlete’s individual characteristics or physical condition, it may not have the promised benefits.
“The purpose of the study,” says Carmona, “was to classify people according to the muscle damage after high-intensity eccentric exercise.”
To do so, thirteen volunteers performed six sets of ten repetitions of a leg-curl exercise at supramaximal intensity, in which the weight was raised externally and the athletes had to lower it gradually for three seconds. Before and after the exercise and over seven days, the force-generating capacity (FGC) was analyzed, the concentration of various serum muscle enzymes was determined (which gives a measure of muscle damage), and functional magnetic resonance was used to identify which muscles had worked the hardest.
Study results and conclusions
Both the decrease in the force-generating capacity and the increase in serum muscle enzymes led to the identification of two groups of people according to their muscular response: those who showed severe damage, and those with moderate damage. The subjects least affected by the exercise were those who normally participate in more physical activity, including sports with frequent sprint accelerations. However, “there was great variability in the response, even in those athletes with a very similar base level,” says Carmona, who highlights an additional contribution of the study:
“The decrease in the force-generating capacity is very similar to the increase in muscle enzymes, which means that this indicator could be used to monitor damage much more easily and without the need for blood samples.”
The study also provided information on “the muscle recruitment dynamics of this type of exercise,” in other words, the elements that most intervene when performing the exercise. Although the generic term “hamstrings” is used, it is in fact a muscle group made up of four different muscles: semimembranosus, semitendinosus and biceps femoris, which has a short head and a long head. “We observed that if there is already fatigue or previous muscle damage, the exercise particularly affects the semitendinosus muscle, and can also impact the biceps femoris short head,” says Carmona. In such cases, which can be detected easily because strength is not completely recovered three days after exercise, “this could increase the injury risk, and it would be better to perform a different exercise or, quite possibly, schedule a rest period.”
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