There is abundant evidence that a moderate amount of running increases health and life-expectancy. However there is also some disconcerting evidence that excessive amount of running might damage health, impair performance and perhaps decrease life expectancy. The main sources of evidence are:
1) One of the most robust predictors of running injuries is volume of training, as demonstrated in a rigorous review by van Gent and colleagues (Br J Sports Med 41: 469-480; 2007)
2) Athletes appear to be at increased risk of developing heart rhythm disturbances such as atrial fibrillation (which leads to increased risk of stroke) and perhaps even more dangerous rhythms such as ventricular tachycardia, as discussed in my recent posts.
3) Some recent evidence suggests that large training volume is associated with increased stiffening of the walls of the arteries which creates a risk of elevation of blood pressure, and also a risk of heart attack. http://abcnews.go.com/Health/HeartDisease/coronary-plaque-plague-long-distance-runners/story?id=10140233. Increased calcification of the arteries might arise from chronic inflammation.
4) The data for physical deterioration with age in athletes is rather inconsistent, but some studies demonstrate that athletes suffer a more rapid deterioration of the VO2max with age than sedentary individuals (Tanaka and Seals, J Appl Physiol 95: 2152–2162, 2003)
5) Excessive training can produce an over-training syndrome which has some similarities to chronic fatigue syndrome. This impairs athletic performance and tends to be associated with features such as weakened immune responses that jeopardize health.
These rather disconcerting observations must be set against the much larger body of evidence demonstrating beneficial effects of running on health. Nonetheless, it appears that the relationship between health benefits and training volume might have an inverted U shape, such that the optimum health is achieved at some intermediate value of training volume. Similarly, the relationship between performance and training volume also exhibits an inverted U shape.
Are the sweet spots fixed by our genes?
These observations raise several important questions. First, is the sweet spot at which training volume produces maximum health benefits the same as the sweet spot that produces peak performance? Secondly, is the location of either or both of these two sweet spots adjustable. In other words, can we move the sweet spots to a higher training volume by appropriate training strategy, thereby promoting greater heath and greater peak performance.
The answer to the second question is almost certainly yes, a sensible training strategy that builds up training volume gradually allows us to cope with a higher training volume and hence to achieve a higher peak performance. It is also probable that we can move the sweet spot for health benefit to a higher level. To maximize our chance of success in moving either or both of the sweet spots to a high training volume, we need to understand something about the way in which training produces either benefit or harm.
The nature of the training effect
It is widely accepted that training produces stress on the body which results in damage and a short term loss of power but produces a adaptive response during subsequent recovery that makes us fitter than before. There are several mechanism that produce this training effect.
First, oxidative metabolism (required to fuel muscle contraction) produces reactive molecules known as reactive oxygen species (ROS) that have the potential to damage the proteins and the DNA in the cells of our body by a process of oxidation. However, the production of moderate quantities of ROS mobilizes the body’s defense against ROS and this can make the body’s tissues even stronger. (Incidentally, the probable reason that antioxidant supplements are not generally beneficial is that such supplements might suppress the body’s own defense system.).
Secondly, mechanical damage to muscle fibres releases chemical messengers that mobilize satellite cells (precursors of muscle fibres) causing them to fuse with muscle fibres resulting in hypertrophy.
In a more general sense, anything that causes tissue damage – either gross trauma or release of local toxins, is likely to produce an inflammatory response which promotes repair, but if there is inadequate opportunity for the repair process, the inflammation might become chronic and produce long lasting damage, as discussed in my post two weeks ago.
The nature of the training response provides support for several of the strategies that have been developed by coaches and athletes on the basis of trial and error, and offers guidance in how best to deploy these strategies.
Assessing adequate recovery
The most important principle is that training must be followed by adequate recovery. However, this principle leaves two questions unanswered. First: how much recovery is needed. The traditional answer is to listen to the body and indeed that is a good starting point. However it is almost certain that we can do better by monitoring apsects of body physiology that reflect the amount of stress the body is experiencing. Of these measurements, Heart Rate (HR) and Heart Rate Variability (HRV) are of the greatest practical utility for the amateur athlete. However interpretation of both HR and HRV has several pitfalls and I am currently in the process of reviewing the evidence for the best way of dealing with these pitfalls.
Optimizing training strategy
The second unanswered question is what program allows us to achieve the optimum balance between training and recovery. I do not think there is a single answer. It depends on the individual and on their goals. In particular, the question of focus on high volume or high intensity has no single answer. When the main goal is increasing speed at the anaerobic threshold (probably the most important predicator of performance over distances from 5Km to the half marathon) either high volume, high intensity or a combination of both can be effective. However this does not mean that it does not matter what program we follow. It means we need to be a little subtle in making our choices to give the best result. When the goal of maintaining a moderately high level of performance over a period of many years is added to the ‘wish list’ we need to be even more subtle in making our choices.
The major options are:
1) periodization – an essential feature introduced in a systematic way by Arthur Lydiard. While Lydiard’s observation of the need to divide the training program into base-building and peak periods appears very sound, the science that Lydiard introduced to justify the nature of the base-building period is questionable, and I am still dubious about the universal suitability of any simplistic conclusion such as the proposal that a large training volume is the most important feature of base building.
2) Variety within each period of a periodized program. In fact Lydiard did recommend variety and in particular, included some speed work and hill work even during base building. I think the scientific evidence (which I reviewed in several of my posts in April 2009) suggesting that at least a moderate amount of work above the anaerobic threshold does not damage the aerobic base, provides us with even greater flexibility in planning the base-building phase than Lydiard might have proposed .
3) Cross-training. In light of the clear evidence that eccentric muscle contraction produces substantial damage to muscles, I believe that cross training is a very valuable way of producing useful metabolic adaptations and increases in capillary density that improve aerobic capacity, while producing minimal eccentric damage to muscle. Hence, I do a substantial amount of my aerobic training on the elliptical cross trainer. There are several caveats that must be added. First, elliptical training and running both load the heart, so it is important to make sure that sparing the leg muscles does not result in undue load on the heart. I use HR and HRV to monitor this. Secondly, it is important to ensure that the leg muscles have been adequately conditioned to cope with eccentric stress before racing, so a substantial amount of running is essential at all stages of the program and running should become the major component in race preparation.
The observation that elite athletes tend to have a limited duration of tenure at the top of the rankings, even after allowing for age, suggests that the strategies used by many elite athletes have not been optimal for ensuring longevity. Maybe this is because it is impossible to make the two ‘sweet spots’ coincide. Perhaps the optimum training load for achieving one’s peak performance is higher than the optimum training load for maximizing longevity. I suspect this might be the case, but nonetheless, think it is worth while to do what we can to bring the two sweet spots as close together as possible, so that we can achiever our peak performance with only minimal damage to our potential longevity – longevity of both running performance and general health . Perhaps the most important ingredient for achieving this is the judicious use of rest or low intensity training when the body is showing signs of stress. This brings us back to the question of monitoring body stress, a topic to which I will return subsequently.