Specificity of training and cross-training

Physiological adaptations in response to physical training are highly specific to the nature of the training activity. Furthermore, the more specific the training program is to a given sport or activity, the greater the improvement in performance in that sport or activity. The concept of specificity of training is very important for all physiological adaptations.

This concept is also important in testing of athletes. As an example, to accurately measure endurance improvements, athletes should be tested while engaged in an activity similar to the sport or activity in which they usually participate. Consider one study of highly trained rowers, cyclists, and cross-country skiers. Their VO₂max values were tested while they performed two types of work: uphill running on a treadmill and maximal performance of their specific sport activity. The important finding, shown in figure below, was that the VO₂max values attained by all the athletes during their sport-specific activity were as high as or higher than the values obtained on the treadmill. For many of these athletes, VO₂max values were substantially higher during their sport-specific activity.

A highly creative design for studying the concept of specificity of training involves one-legged exercise of specificity of training involves one-legged exercise training, with the untrained opposite leg used as the control. In one study, subjects were placed in three groups: a group that sprint trained one leg and endurance trained the other, a group that sprint trained one leg and did not train the other, and a group that endurance trained one leg and did not train the other. Improvement in VO₂max and lowered heart rate and blood lactate response at submaximal work rates were found only when exercise was performed with the endurance-trained leg.

Much of the training response occurs in the specific muscles that have been trained, possibly even in individual motor units in a specific muscle. This observation applies to metabolic as well as cardiorespiratory responses to training. Table below shows the activities of selected muscle enzymes from the three energy systems for untrained, anaerobically trained, and aerobically trained men. The table shows that aerobically trained muscles have significantly lower glycolitic enzyme activities. Thus, they might have less capacity for anaerobic metabolism or might rely less on energy from glycolysis. More research is needed to explain the implications of the muscular changes accompanying both anaerobic and aerobic training, but this table clearly illustrates the high degree of specificity to a given training stimulus.

Selected muscle enzyme activities(mmol x g-1 x min-1) for anaerobically trained, and aerobically trained men
	Untrained			Anaerobically trained		Aerobically trained
Aerobic enzymes
Oxidative system
Succinate dehydrogenase			8.1		8.0		20.8
Malate dehydrogenase			45.5		46.0		65.5
Carnitine palmytil transferase			1.5		1.5		2.3
Anaerobic enzymes
ATP-Cr system
Creatine kinase		609.0			702.0		589.0
Myokinase		309.0			350.0		297.0
Glycolytic system
Phosphorylase		5.3			5.8		3.7
Phosphofructokinase		19.9			29.2		18.9
Lactate dehydrogenase		766.0			811.0		621.0

Cross-training refers to training for more than one sport at the same time or training for several different fitness components(such as endurance, strength, and flexibility) at one time. The athlete who trains by swimming, running, and cycling in preparation for competing in a triathlon is an example of the former, and the athlete involved in heavy resistance training and high-intensity cardiorespiratory training at the same time is an example of the latter.

For the athlete training for cardiorespiratory endurance and strength at the same time, the studies conducted to date indicate that gains in strength, power, and endurance can result. However, the gains in muscular strength and power are less when strength training is combined with endurance training than when strength training alone is done. The opposite does not appear to be true: improvement of aerobic power with endurance training does not appear to be attenuated by inclusion of a resistance training program. In fact, short-term endurance can be increased with resistance training. Although earlier studies supported the conclusion that concurrent strength and power, one well-controlled study did not show this. McCarthy and colleagues reported similar gains in strength, muscle hypertrophy, and neural activation in a group of previously untrained subjects who underwent concurrent high-intensity strength training and cycle endurance training compared with a group who performed only high-intensity strength training.