TRAINING
Age and Gender Influences on Training Adaptations Steve Bird
Introduction In response to the article on ‘gender differences’ published in the last edition (AO-June’08), I’ve had a number of requests to expand on certain aspects. So in this article I’ll briefly look at some of the issues concerning age and gender influences on adaptations to training. This is a complex area given the number of variables involved, such as the type of training, intensity, frequency, fitness level, and so on. And at the moment there are a number of gaps and inconsistencies in the research - so I’ll be presenting what I believe to be the current consensus, although we may see it evolve as our understanding of exercise physiology continues to grow. Training responses and adaptations Firstly, regardless of age or gender, some people adapt more rapidly to training than others. That is to say, they get fit quicker, and perhaps can attain higher eventual fitness levels. In recent years biotechnology has enabled studies into whether this has a genetic basis, and there is some evidence for the involvement of the Angiotensin Converting Enzyme (ACE) gene, amongst others, although at the moment findings are inconsistent and more work is required 1. Another factor affecting adaptations to training is the individual’s current training status. That is to say, how close they currently are to their hypothetical peak. Those who are untrained have greater capacity to improve substantially from their low starting values, whereas someone who is already highly trained may only make small further improvements with continued training - which are of course nevertheless important at the elite level. Nutrition is another important factor, and it is well established that a good, healthy diet that contains plenty of carbohydrate is vital to support large amounts of training. It is also well established that inadequate nutrition will impair the effects of training, as the body will be unable to maximize any improvements to its anatomy and physiology, as well as being unhealthy. However, beyond this the general consensus is that most supplements don’t augment the effects of training – provided you have a good nutritious diet 2,3. A possible exception to this is creatine supplementation for developing strength, power and muscle mass, in younger and older people 4-6.
Hormones Training places physiological demands on our bodies, which respond by making improvements to our physiology and 34 THE AUSTRALIAN ORIENTEER SEPTEMBER 2008
tissue structures. It’s these adaptations that make us fitter, and underlying this myriad of training induced adaptations is our endocrine (hormonal) system. Of particular pertinence are the levels of anabolic (growth promoting) hormones such as testosterone, Growth Hormone (GH) and Insulin Like Growth Factors (IGFs). And it’s the difference in circulating values of these between men and women, and their decline with increasing age that has been proposed to be the cause of gender differences in the rate and magnitude of many training adaptations.
Adaptations by Age and Gender In younger adults, aerobic training such as running will promote an increase in capacity to utilize oxygen (VO2max). One of the reasons for this is an increase in the chamber size of the left ventricle of the heart. This means that the heart can eject more blood with each beat whilst exercising strenuously - a parameter known as its maximum Stroke Volume (SVmax). Consequently it can deliver more oxygen to the exercising muscles. Another adaptation occurs at the muscles, whereby training increases the muscles’ ability to extract oxygen from the blood passing through it. The difference between the amount of oxygen in the blood going to the muscles through the arteries and that returning to the heart from the muscles via the veins is called the a–vO2 difference. Trained muscle can extract more oxygen and therefore a trained person will have a greater a–vO2 difference. Studies in previously untrained older people have shown that older (>60 yrs) men and women can increase their VO2max. In the study by Spina et al. 7 the relative increases were similar in men and women (19% and 22% respectively), although the men had larger absolute values. However, the physiological adaptations underlying these increases appeared to differ. For example the men increased their maximum Stroke Volume by an average of 15%, which accounted for 66% of the increases in VO2max, and increased their a–vO2 difference by 7%, which accounted for the remaining 34% of the increase in VO2max. Whereas the women exhibited no change in their maximum Stroke Volume and their entire increase in VO2max was attributable to an 18% improvement in their a–vO2 difference. However, it should be noted that these studies were conducted with previously untrained individuals and the implications for older orienteers, who may have had many years of training before reaching an older age, are unknown. Other studies comparing older and younger men (again previously untrained), show that although older men do increase their SVmax with training (as indicated above), the amount of improvement is less than that seen in younger men 8. And other studies suggest that the ability to increase SVmax declines with age, and that with increasing age, improvements in VO2max become more dependent on improvements in a–vO2 difference 9. So ageing appears to not only reduce the magnitude of these improvements, but also the modality of the underlying changes, and may be associated with reduced levels of circulating anabolic hormones. A similar scenario is seen with resistance training. Muscular strength increases can be attributed to increases in muscle mass (muscle hypertrophy), and non-hypertrophic adaptations, such as improvements in the neurological recruitment of the muscle fibres. And whilst men and women of all ages can increase their muscle strength and muscle mass, it would appear that younger people are able to increase their strength by more than older people, and men by more than women 10. Furthermore, it would appear that the strength increases in women are more reliant on the non-hypertrophic adaptations, whereas the men rely more on the increases in muscle mass 11. Again these differences are attributed to differences in levels of circulating anabolic hormones.
