Tendons transmit the force from our muscles to the bones, and proper interaction between the muscles and tendons is very important for the athlete’s performance and to prevent injuries in sports.
With muscle contraction (tension), the tendon stretches and remains so while the muscle is contracted. When a strong muscle pulls a “weak” tendon, it can stretch very much (Fig. 1). This, in turn, can lead to micro-injuries, ruptures in the fibers of the tendons.
When a tendon stretch occurs frequently, and it does not have time to heal, this can ultimately lead to injuries such as tendinopathy. When a muscle grows stronger and larger, the tendon must “adjust” to prevent excessive tension and related damage. Increased stiffness of tendons allows them to stretch less and serves as a protective mechanism.
Thus, strong muscles need stiff tendons.
Upper images: Left: imbalance between muscle and tendon properties. A strong muscle (large cross-sectional area) pulling on a compliant tendon results in a high tendon strain. Right: balance between muscle and tendon properties. Muscle contraction results in lower tendon strain.
Why Do We Have to Prevent Injuries in Sports
Imbalance due to training
Muscles and tendons adapt to mechanical stress and are sensitive to mechanical stress. The process by which a mechanical stimulus is transformed into a biochemical response is called mechanotransduction.
Due to the biochemical response, adaptation occurs. But the time of adaptation and the mechanical stimuli that cause these adaptations can differ in the tissues of muscles and tendons. Recent in vivo experiments (in a living organism) have shown that high-intensity training leads to adaptations in tendon tissues. It was also shown that a moderate duration of exercise (3 seconds + relaxation) led to better adaptation, as opposed to shorter (1 second + relaxation) or longer (12 seconds).
Thus, training, especially plyometric (jumping training) or with low intensity, can lead to an imbalance between the muscles and tendons, and ultimately lead to injuries.
In a recent cross-sectional study, Mersmann and colleagues found that volleyball players have a greater imbalance in the strength of the extensor muscles of the knee joint and patella compared to just active people of their own age. The authors suggested that this imbalance may contribute to damage to the patellar ligaments as a result of plyometric training.
A weaker tendon with respect to a stronger muscle can lead to a tendon injury, but too stiff tendon with respect to a weaker muscle can also lead to injury. The stiff tendon is less stretched, for example, the Achilles tendon during running.
A “weak” tendon can lead not only to injuries but also to poor athletic performance, as performance decreases due to a faster reduction of muscle fibers. As a result, power indicators are worse. The too stiff tendon can also lead to poor performance. Therefore, finding the “golden mean” not only reduces the risks of injuries but also positively affects the athlete’s performance.
Steps on How to Prevent Injuries in Sports
What is needed for balance? Imbalance can be avoided with regular strength training. For exercises to be effective for muscles and tendons, they must meet several criteria:
- Mechanical load
In vivo experiments show that a stretch of about 5% is optimal for training tendon stiffness. These results are consistent with the results of another recent work in which a commensurate stretch resulted in the greatest increase in phosphorylation.
In both in vivo and in vitro experiments, lower loads (with lower weights) led to less adaptation/phosphorylation. In order to get a sufficient load on the tendon, the muscle must contract greatly. Using a weight of more than 85-90% of the maximum voluntary contraction leads to a strong contraction of the muscles and a sufficient load (~ 5%) on the tendon to lead to adaptation.
- Duration of loads
With a short duration of loads, for example, as with plyometric training, the adaptation process in tendon tissues decreases. In vivo studies show that the duration of contractions of about 3 seconds with a rest period of 3 seconds leads to adaptation of the tendons, which indicates effective mechanotransduction (the process through which forces and other mechanical signals are converted into cellular signals).
Shorter (1 second) and longer (10 seconds) contractions led to a decrease in phosphorylation.
- Rest period
Unfortunately, no in vivo studies have been conducted to determine the optimal rest period between sets. Only in vitro experiments studied the effect on the tendons of repeated training without rest and with a rest period of about 6 hours. Evidence suggests that at least 6 hours of rest is required between tendon workouts.
- Other factors
Although the type of contraction — concentric, eccentric, or isometric — is not critical to tendon adaptation, it is important to consider some of the advantages and disadvantages of different types of workouts.
In dynamic – concentric-eccentric – training, the tendon experiences great stresses only for some time. Therefore, it is recommended to increase the duration of the exercise to about 6 seconds so that the stimulus is sufficient for effective mechanotransduction. You can also do those exercises in which the load on the tendons is high, for example, the 60-degree knee flexion in a back squat for the patella tendon.
The advantage of isometric training is that duration and intensity are easier to control than dynamic exercises. Exercise can also be modified more easily so as not to injure tendons. Isometric exercises are recommended to be performed 3 times a week, with approximately 2 minutes of a break between sets (Fig. 2).
It has been suggested that training with low mechanical stress, such as calf raises, can lead to an imbalance between the strength of the muscles and tendons, as low mechanical stress has more effect on the muscles than on the tendons. A recent systematic review showed that high-intensity strength training has potential advantages over eccentric exercises in Achilles tendon tendinopathy, although the effect is small.
Several studies have used the relatively long duration of muscle contractions to treat the tendinopathy. For example, Rio and colleagues found that isometric muscle contractions reduce long-term pain in people with patellar tendinopathy. However, recent studies have not found the same effect in patients with Achilles tendon tendinopathy.
With tendinopathy, it is possible to be injured, and when the damaged tendon is loaded, healthy tendon tissue “protects” the less durable and injured tissue. Since healthy fibers are tenser, damaged ones do not receive incentives for adaptation. This can be solved with the help of the so-called “relaxation of stress.” As the intact collagen fibers slowly relax, the damaged tissue becomes more “loaded” and thus adapts.
Gelatin to prevent injuries in sports
Recently it was shown that taking 15 g of gelatin in combination with ~ 225 mg of vitamin C an hour before training leads to an increase in collagen synthesis compared to placebo. This can be used to prevent injuries or during rehabilitation in combination with the previously described exercises.
A recent study, in which 18 people took part, showed that physiotherapy exercises with tendinopathy of the Achilles tendon gave better results with the intake of 2.5 g of gelatin 30 minutes before the exercises.
We also recall that hydrolyzed collagen has greater bioavailability. 15 g of collagen hydrolyzate per day is equivalent to 15 g of gelatin, and even more because of the better ability to assimilate.
- Imbalances in muscle and tendon strength and the relation with injuries and performance – Van Hooren B.
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