Interplay of Load and Recovery in Endurance Training

Homeostasis

In our body, the individual components are constantly being built up and broken down. Proteins have an average lifespan of 3 to 15 days, which means that new protein mass must be produced constantly. Every day, roughly 3 to 6% of the protein content in active tissue is replaced by new protein. Even though erythrocytes (red blood cells) on average exist a little longer, at about 120 days, we also need a constant new production to maintain the hemoglobin concentration and thus the oxygen transport capacity.

This process of continuous remodeling of body tissue is called homeostasis. A balance between building-up and breaking-down processes (anabolism and catabolism) is of the utmost importance. If one of these two processes predominates, body mass will inevitably change. This can happen in a positive way (muscle building and fat loss in athletes) or in a negative way (muscle atrophy and tumor growth in cancer patients).
If homeostasis is disturbed in any way by internal or external stimuli, a homeostasis disturbance occurs. This in turn leads to adaptations at the cellular, organ or systemic level. Recovery is necessary for this.

Supercompensation

The phenomenon of supercompensation describes the process of the body adapting to a homeostasis disturbance that has occurred. Ideally, a training-induced loss of substance is not only compensated but even overcompensated, which results in a physical improvement of the trained structure. Overall, through this adaptation the organism is better prepared for similar loads in the future. However, if supra-threshold training stimuli (homeostasis disturbances) fail to occur in the future, training progress will regress.

Not all training-related adaptations of the body can be adequately described by the concept of supercompensation. While in strength training the adaptations through the induction of protein biosynthesis can be described in detail, the body's adaptation effects to coordination training via neural plasticity and other learning effects are not yet fully understood.

Nevertheless, especially in endurance training, the concept of supercompensation is suitable for describing training progress and adaptation effects. One of these adaptations is the altered glycogen metabolism after endurance training. Hickner et al. 1997 were able to show that glycogen synthesis is significantly increased after 2 hours of endurance training. Moreover, in the previously trained study population they found a greater change in this very adaptation than was the case in untrained individuals.

Fatigue and Overtraining

Endurance training leads to fatigue of the organism. Fatigue processes can be detected not only in the periphery (=muscles) but also in the central nervous system (CNS). Causes of fatigue can be strong accumulations of metabolic intermediate and end products (lactate, elevated urea levels, etc.), as well as a strong depletion of energy stores and reserves of hormones and enzymes. After endurance training, it is important to give your body rest so that it can recover. If the balance between load and recovery in training shifts to the detriment of recovery, so-called overtraining can occur. The symptoms of overtraining can be psychological and somatic in nature.

Symptoms and signs of overtraining can include the following: performance drops despite training; loss of muscle strength and coordination, decreasing performance capacity; general tiredness, changes in appetite, weight loss, sleep disturbances, easily irritated, restless, quickly aroused, quickly agitated, becoming anxious or nervous, lack of motivation, concentration problems, depressive mood, elevated resting heart rate. Not all signs have to occur together in overtraining. However, if a single sign appears, this is not a diagnosis of overtraining either. To get out of the vicious cycle of overtraining, you must greatly reduce or completely stop your training intensity.Prolonged neglect of recovery can, as mentioned, lead to overtraining. To maintain or continuously improve your athletic form, recovery after the load is essential. Training load and recovery are closely linked and mutually dependent.

Tapering (reduced training volume) involves a reduction in training intensity and volume. This is carried out especially before competitions. This reduction allows the body to fully refill its energy reserves in order to achieve the best performances. It is important to note that tapering should not be carried out for too long. If it is, this is called detraining. This involves a partial or total loss of training-induced adaptations. You can no longer deliver the performance.

Recovery: Measures and Recovery Times

Recovery

As already explained, the balance between load and recovery should always be kept in equilibrium in order to prevent any kind of overtraining. During the recovery phase of training, the body's goal is to recover completely. Ideally, an adaptation process takes place that enables the body to be better prepared for a recurring load. To give the body the opportunity to recover optimally, the processes of fatigue and the regeneration processes must at least be roughly understood. During training, various fatigue processes take place, which often manifest themselves through empty energy stores or an imbalance in various metabolic processes. For example, after intensive interval training, the energy reserves are largely exhausted and the enzyme activity of the metabolic processes decreases after the training.

Disturbances in water and electrolyte balance also belong to the fatigue phenomena of intensive training.
On the one hand, it is of central importance to provide the body with the necessary nutrients and above all the time for complete recovery. On the other hand, there are ways to support the regeneration processes. These include educational, medical-biological and psychological measures. While educational measures mainly involve sensible training design, physiological recovery processes are optimally supported through the use of sauna, massages and adapted nutrition. Psychological measures, on the other hand, serve mainly to relax and to eliminate negative psychological factors such as anxiety, nervousness or tension.

Recovery Times After Endurance Training (Hegner 2015)

Load | Complete recovery
Aerobic | 24-28h
Mixed aerobic-anaerobic | 24-36h
Anaerobic-alactic and -lactic | 48-72h