Training adaptation: the histamine connection

Although many recreational athletes train simply for enjoyment and health, most competitive athletes undertake a training program in order to improve their performance. This might involve improving endurance capacity – for example, being able to run/cycle/swim further - or becoming stronger and more powerful, or any combination of these traits. Regardless of the precise desire or outcome however, the goal of a training program designed to improve performance is to induce enough of a biochemical and physiological stimulus in a training session to induce a training adaptation.

What is training adaptation?

Training adaptation occurs as a result of a training stimulus or demand, and is designed to help the body become better at withstanding that stimulus and meeting that demand the next time around. When it comes to endurance sports such as running, swimming, cycling, rowing etc, there are a number of adaptive processes that occur as a result of endurance training. These include:

·       The removal of debris and various metabolites associated with exercise (eg lactate, protein fragments from exercise-induced muscle damage).

·       Repair to muscle fibres, which sustain micro-tears, particularly during intense or unaccustomed bouts of exercise.

·       An increase in the production of relevant muscle enzymes – eg, those needed for energy production in various energy pathways, or involved in muscle protein synthesis. A key enzyme for developing endurance capacity in muscle fibers is ‘AMP-activated protein kinase’ (AMPK for short) AMPK is activated by endurance exercise, especially when that endurance exercise is intense⁽¹⁾. For muscle protein synthesis, a signalling molecule known as the ‘mammalian target of rapamycin complex 1’ (abbreviated mTORC1) is particularly important (see this SPB article for an in-depth explanation)⁽²⁾.

·       Increased activity of genes involved in the synthesis of mitochondria (the cells’ energy factories), such as two genes designated ‘MT-RNR2 (16S rRNA)’ and ‘MT-RNR1 (12S rRNA)’⁽³⁾.

·       Replenishment of stored muscle carbohydrate (glycogen).

Maximizing training adaptation

One of the goals of a well-sorted training program is (or should be) to maximize the adaptation stimulus delivered by training sessions, without overloading the athlete and inducing excessive fatigue or even an overtrained state. However, it’s important to realize that the amount of training adaptation that occurs following a training session is not just about the training stimulus delivered, but also what happens post-training – ie ensuring there is adequate rest and post-exercise nutrition to facilitate recovery, which is when adaptation occurs. If training is optimal but post-training rest and nutrition are not, your training adaptation will not be as complete as it could be.

Impediments to training adaptation

Not getting adequate rest and nutrition post training can impair training adaptation, but there are other potential adaptation impediments. In a previous article by SPB contributor Rick Lovett, we looked at research showing that some so-called recovery strategies such as ice baths and/or cold-water immersion may impair training adaptation. As Rick explained, research shows that routine ice baths after training sessions might make you feel better, but they might impair adaptation and could make you slower in the longer term.

For example, one study put a dozen college-aged men on stationary bicycles and had them spin at moderate intensity (about 70% of VO2max) 3-4 times a week in 4 to 6-week block of training⁽⁴⁾. Another 11 volunteers used handgrip exercises over the same period to strengthen their forearms. Following each workout, the research subjects stuck one limb in an ice bath at temperatures ranging from 5°C (for the cyclists) to 10°C (for the forearm-strengthening group). The other limb stayed at room temperature, allowing each participant to serve as their own control — see figure 1. At the end of training block, the cyclists’ non-ice-bathed legs had gained more strength, more blood circulation, and more endurance than their ice-bathed ones. Even VO2max (measured in single-leg tests) had gone up more than in the ice-bathed legs. The strength findings were similar; the chilled arms had gained 11 percent in strength, while the un-chilled ones had improved by 16 percent!

Figure 1: Experimental protocol for chilled vs. unchilled limb training