There is little doubt that if you wish to run well, a large part of your training should involve running. Running requires a specialised pattern of muscle activity that must be practised. It also subjects the body to unique stresses to which the body must adapt. Gradual build-up of running itself is almost certainly an imporant part of acquiring the skill and adapting to the unique stresses. In other words, training should be specific. However, the principle of specificity has important limitations. You do not become a good marathon runner merely by running marathons at your best race pace repeatedly. This will merely lead to exhaustion. The principle of specificity does not extend to exclusive training at race pace over the relevant distance. We need to build up a variety of strengths and abilities and training should be adapted in a manner that allows the development of each of these strengths and abilities to the full extent without exhausting the body. This leads to the question of whether it is more effective to include some cross-training activities other than running, in order to build specific strengths with minimal stress, and if so, what proportion of training should be cross-training.
The first point to make is that the answer almost certainly depends on the individual. Some individuals have achieved superlative performances with little or no cross training. Among these is Ed Whitlock, undoubtedly the most successful elderly distance runner the world has seen; holder of more than 45 age-group world records, spanning distances from 1500m to marathon, in age groups ranging from 65-69 to 85-89. His training consists of low-intensity running for several hours each day, together with fairly frequent races at shorter distances. He does no cross training at all.
However, if one examines Ed’s training in more detail, it is clear that he has crafted it carefully in a way that scrupulously avoids the stress of extensive amounts of running at or near race pace. He describes his training pace a glacial. He shuffles along with a short stride, scarcely becoming airborne, for the explicit purpose of minimising impact stresses on his legs. Despite the fact that all of his explicit training is actually running, it is running in manner so different from his race pace and gait that one might almost be tempted to call it cross-training. Nonetheless, it does involve the essential elements of running, albeit with one of running’s defining features, getting airborne, almost entirely removed.
At the other extreme is Dean Karnazes, ultra-distance runner famed for prodigious feats of endurance such as the Badwater Ultramarathon, which he won in 2004. In his own words, he is very eager to try any form of cross training that presents itself. At various times he has advocated the elliptigo, an elliptical cross-trainer on wheels designed to mimic the movements of running but with no impact forces, and more recently, the Zero Runner, in which the mounting rods of the platforms that you stand on are hinged at the level of foot and knee. The leg action even more closely resembles that of running, yet impact forces are abolished. Karnazes also emphasizes the importance of whole body training, including a wide range of strength exercises
There are few noteworthy examples of elite runners who have been forced to rely almost entirely on cross training. Three months out from the Beijing Olympics, Paula Radcliffe suffered a stress fracture of her femur and was forced to rely heavily on elliptical cross training and pool running. She did complete the race in 23rd place, in a creditable but intensely disappointing time of 2:32:38. The images of her struggling after the first 19 miles of the race are almost as pitiful as the pictures of her sitting beside the road in Athens 4 years previously when she dropped out of a race that many expected would be the crowning glory of a phenomenal few years in which she had taken ownership of the women’s marathon. The fact that in Beijing Paula was able to keep up with the leading pack for the first 19 miles indicates that her cross training produced impressive aerobic fitness, but the cross-training was inadequate to condition her legs to withstand the repeated trauma of impact. In her words: ‘My calf stiffened up and the pain went all the way up my leg. By the end, I was running on one leg’.
It is clear that different athletes have incorporated cross training into their training routines for various reasons and to a varying extent, with varying levels of success. In my recent series of articles on strategies for enhancing longevity as a runner, I had concluded that the evidence suggested that cross training has an important role to play. I will finish this article with an overview of the aspects of a runner’s physiology that might be developed effectively by cross-training, and in subsequent articles, will examine the virtues and limitations of a range of different forms of cross training, including resistance exercises and plyometrics; elliptical cross training, cycling, walking and swimming.
The heart’s capability to pump a large volume of oxygenated blood via arteries to muscles, together with the ability to sustain high cardiac output over prolonged periods, are key components of aerobic fitness. Virtually all forms of cross training enhance the pumping capacity of the heart. The various forms of low-impact aerobic exercise, especially cycling, elliptical cross training, aqua jogging and swimming offer the possibility of maintaining a high cardiac output for sustained periods with minimal trauma to the musculo-skeletal system. They contribute to the development of cardiac endurance by mechanisms such as increasing the capacity of heart muscle to utilise fats, while also enhancing capillaries within cardiac muscle itself that are essential for delivering oxygen to the heart muscle fibres. Low-impact aerobic training can also be incorporated in high intensity interval training, providing a time-efficient way of increasing cardiac output, largely by increasing stroke volume.
As in the case of heart muscle, long duration aerobic cross-training develops the ability of skeletal muscle to metabolise fat and also enhance the capillary supply to the muscle fibres Resistance training can be used to develop skeletal muscle strength and power in an efficient manner by employing loads that exceed those involved in running. Plyometric training is a very efficient way of enhancing power of eccentric contraction and developing resistance to damage from eccentric contraction, but unlike low-impact forms of cross training, plyometric exercises carry a serious risk of trauma to muscles, tendons and ligaments. Hence plyometrics should be incorporated in a training program cautiously, gradually build-up of the intensity of the eccentric contractions. However provided build-up is gradual it is possible to apply far greater forces than occur during running itself. This generates reserve capacity to manage eccentric contraction, resulting in a more powerful running action together solid protection against injury
Systemic metabolism and hormones
Both long duration low intensity aerobic cross training and short duration high intensity cross training promote many of the metabolic and hormonal responses that are crucial for endurance running and for the repair of tissues. For example, low impact cross training in the mid to upper aerobic zone is potentially an effective way to enhance the capacity of the lactate shuttle that transports lactate to liver where it is converted back to glucose and stored as glycogen. High intensity cross–training can enhance the capacity to transport potassium that is released from muscle during contraction, back into muscle, thereby making the muscles more resistant to fatigue. Both aerobic exercise and resistance training can promote growth hormone release, though in general résistance training is more effective for stimulating growth hormones and other anabolic hormones.
A moderate body of evidence indicates that low intensity activity following strenuous training promotes potentially beneficial physiological changes, such as a decrease in blood levels of reactive proteins that are marker for inflammation. However the evidence that such changes actually enhance subsequent performance is sparse. Perhaps the most convincing evidence comes from the study led by Peter Peeling at University of Western Australia, in which nine triathletes performed an intense running interval session on two separate occasions followed 10 hours later by either a swim recovery session (consisting of 20 × 100 m at 90 % of 1 km swimming time-trial speed), or a passive recovery session of similar duration. On each occasion, on the day following the interval session, they performed a high-intensity treadmill run to fatigue to assess the degree of recovery of running performance. The athletes were able to run for an average of 13 minutes, 50 seconds after swimming recovery compared to only 12 minutes, 8 seconds after lying still for recovery. Furthermore, the swimming recovery was associated with significantly lower levels of c-reactive protein 24 hours after the interval run. Thus the swimming recovery was not only associated with reduction in a protein marker of inflammation but also with enhanced performance in the treadmill running test, 24 hours later. Peeling and colleagues speculated that the non-weight bearing character of the swimming recovery was likely to be an important factor in the benefit
Overall, the various different forms of cross training can enhance the capacity of many of the physiological functions that are essential for distance running, while minimising the damage from impact at foot fall that is inevitable during running itself. The diversity of different benefits from different forms of cross training make it possible to target specific weaknesses where necessary. Alternatively, incorporating a diverse range of cross training activities in your training program can deliver benefits in a wide range of physiological functions while minimising the accumulation of stress on the body.
The experience of Paula Radcliffe in Beijing suggests that a distance runner must nonetheless do a substantial amount of actual running. On the other hand, a broader perspective on her career raises a more challenging question. Despite standing head and shoulders above all female marathon runners in history, her career was blighted by injury. Would a more judicious balance between running and cross-training throughout her career have allowed her not only to set an astounding world record far beyond the reach of all others in the current era, but perhaps she might also have won an Olympic medal.