Keith Baar is a renowned sports scientist known for his research on muscle and tendon physiology. One of his most interesting focuses is the concept of the “protective stress mechanism of load” and the “relaxing stress of load.” These terms refer to how the body responds to different types of load and how these responses affect the ability of tissues, especially tendons and muscles, to adapt and strengthen or, conversely, weaken and become more prone to injury.

Protective Load Stress

Protective load stress is the result of a well-applied mechanical load that promotes positive adaptation of connective and muscle tissue. Baar suggests that repetitive, well-dosed load helps tendons become stronger and more resistant. This stress allows collagen fibers in tendons to optimally align and strengthen, promoting a greater capacity to withstand future loads.

For example, when athletes train in a controlled and progressive manner, they subject their muscles and tendons to a load that, over time, makes them more resilient. This is crucial in sports involving repetitive or high-intensity movements, such as soccer, where overuse of certain joints can lead to injury if the load is not properly managed. Baar’s approach emphasizes that applying the right amount of load not only enhances performance but also protects the athlete in the long term.

Relaxing Load Stress

On the other hand, relaxing load stress occurs when the tissue is not adequately challenged, leading to a loss of strength and adaptive capacity. If the body does not receive proper stimulation, as during long periods of inactivity or poorly planned recovery, tendons and muscles can lose their ability to handle loads, making them more vulnerable to injury when mechanical stress is suddenly reintroduced.

This phenomenon is particularly relevant during rest periods or post-injury recovery. If an athlete drastically reduces their workload or does not follow a progressive return-to-activity plan, they may experience relaxing load stress. This often results in a higher likelihood of injury when the athlete tries to return to their previous level of training without proper preparation.

Practical Example: A Soccer Player’s Injury

Imagine the case of a soccer player who suffers an Achilles tendon injury. During the recovery process, applying the principle of protective load stress is crucial. After the initial weeks of immobilization and rest, it is necessary to gradually introduce controlled load exercises, such as progressive walking and specific tendon strengthening exercises. This ensures that the collagen fibers align and strengthen correctly, preventing maladaptation.

However, if after the initial recovery the player abruptly returns to intense training without proper progression, they may experience relaxing load stress. Their tendon, having not been properly challenged during recovery, will not be prepared for the physical demands of the sport, increasing the risk of relapse or a new injury.

Benefits and Risks of the Approach

Keith Baar’s approach can be highly beneficial when applied correctly. For coaches and athletes, understanding how to dose mechanical load can maximize training results and significantly reduce the risk of injury, especially in sports that require continuous muscle strength and endurance. Proper periodization of training, which includes phases of protective stress (progressive load) and adequate active recovery periods, can improve an athlete’s longevity and performance.

However, there can also be risks if applied incorrectly. If the load is not properly dosed, it may cause excessive stress leading to overuse injuries. Conversely, a lack of mechanical stress could result in maladaptations that leave the athlete vulnerable when returning to competition.

In summary, Baar’s approach highlights the importance of balanced loading: applying the necessary stress to generate positive adaptations without pushing the body to the breaking point. When managed correctly, this protective stress mechanism can be a powerful tool for optimizing long-term performance and athlete health.