Endurance Adaptations: Prescription Implications.

What is an adaptation?

Adaptations are the physiological (mechanical, physical, and biochemical) responses after acute and chronic stress is placed on it Adaptations for endurance training can be separated into two major categories: central and peripheral adaptations.

Central

Related to the engine of endurance training and performance; the heart. Specific changes that are observed:

• hypertrophy of the heart. 
• changes in blood and its components (i.e hemoglobin content).
• changes in partial pressures in tissue diffusion, angiogenesis (blood vessel capitalization and growth).

​Central adaptations play an important role in performance in new athletes but can go unchanged in elite athletes. Cardiac output (Q) = Stroke Volume (SV) x Heart Rate (HR) can quantify central components of performance. Central adaptations are the longest to develop, are strongly governed by genetics and are individually impacted by heat, humidity and altitude. 

The brain also plays a "central" role in performance and training. Sport psychology (motivation, self efficacy, visualization) can be a potent tool to implement in training. Often training adaptations whether positive or negative (injury) go hand in hand with changes observed in the mind. There are some prominent voices in exercise physiology who believe the mind can have a profound impact on performance: Tim Noakes, MD - "Lore of Running" - central governor model. 

Peripheral

Peripheral adaptations describe the delivery and utilization of energy to perform mechanical work at the muscular level. Some changes observed:

• increased enzyme concentrations.
• muscle fiber type differentiation.
• intramuscular changes such as fat storage and utilization.
• glycogen storage and utilization.
• oxygen uptake kinetics.
• mitochondrial changes.
• substrate utilization (lactate as fuel and more) and muscle buffer capacity.

Peripheral adaptations are quick to respond to stress and can account for rapid performance changes with training. They are primarily sensitive to intensity, however duration also plays an important role (ex. lactate shuttling and lipidic power). 

These adaptations are extremely complicated and can be affected by multiple stimuli.

Neuromuscular changes are observed in the communication between central (brain) stimuli to the muscles. Specially how this signal is carried and transmitted to cause muscles to contract.  These adaptations are also very sensitive to intensity. Training modalities like sprint training, plyometric or heavy strength training can enhance these adaptations. 

Closing

Training adaptations are complicated (see above). Its important to think of training stress as an organic process instead of being linear. Everything is interrelated and connected. Finally, there are individual responses to all stimuli. What works for one athlete may not work for the other and you have to consider factors such as lifestyle, bio-mechanics, training history, injury history, genetics, age, deficiencies and mental tenancies.

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