Todd Becker at gettingstronger.org writes:
“Based on the fundamental principles of Hormetism, improvement in strength requires adaptive remodeling in response to applied stress. In order to see real improvement, the stress must push the system beyond its current “comfort zone”, by the use of high intensity exercise. One of the best translations of this principle into physiological terms is the book “Body by Science”, by Doug McGuff, an emergency room physician who has extensively studied the physiological adaptations that accompany high intensity exercise.
McGuff makes a strong case that high intensity (HIT) exercise, provides in as little as 12-20 minutes a week provides benefits that cannot be achieved by hours of “aerobics” such as walking, jogging, treadmills, swimming or the like. Many will agree that resistance training will lead to improved muscular strength and help to moderate the risk of injury in running or other sports. But McGuff goes further, arguing that HIT is actually superior to aerobics for improving the cardiovascular system:
Strength training is actually the best way to train the cardiovascular system precisely because, unlike what we refer to as “aerobics”, strength training actually involves and stimulates all the components of metabolism. (BBS, p. 35)
This includes both “anaerobic” metabolism that occurs in the cytosol and “aerobic” metabolism that occurs in the mitochondria. Typical cardio routines such as treadmills and jogging fail to do this:
[L]ow intensity steady state (popularly referred to as “cardio”) activity does not tap the fast-twitch muscle fibers that possess the most glycogen. Consequently the muscles are never emptied of meaningful levels of glucose, with the result that the circulating glucose has nowhere to be stored — except as bodyfat. Moreover, the muscle cells will lose their sensitivity to insulin but become inflamed by the high levels of insulin that the body has produced to deal with the high levels of circulating glucose. The body mortars this inflammation with LDL cholesterol, which puts the low intensity exerciser at greater risk for cardiovascular problems. (BBS, pp. 31-34)
In his book, McGuff makes the case that HIT works effectively only if performed in an intense manner, just short of the point of failure, with slow movements in good form, and with appropriately long periods of recovery to stimulate growth and allow adaptation of the muscle. In Chapter 3, “The Dose-Response Relationship”, he explicitly pursues the improvement of fitness as a hormetic phenomenon:
Both a drug and an exercise act as a stimulus to the body, both require an optimal concentration, both require a dose that is not “too high” and both require an appropriate frequency. The concentration of the drug is analogous to the amount of sets performed in a given workout, and the dosing frequency is analogous to the frequency of exposure to the training stimulus. Also, just as with medicine, there exists in exercise a “narrow therapeutic window” within which the volume of exercise can act to stimulate the body to produce a positive adaptive response that is optimal.
McGuff goes on to explain how the body, when challenged with exercise, recruits muscle fibers in a fixed order, according to what is demanded. When the physical demand is low, the body will prefer to recruit the Type I or Slow Twitch muscles. It will only recruit the higher types IIA, IIAB and IIB (Fatigue Resistant, Intermediate Fatigubility and Fast Twitch or Glycolytic) fibers as the intensity of the demand increases. The fast-twitch fibers are the ones that tax the glycolytic pathways, leading to an adaptive response. But these same fast-twitch fiber fatigue easily and require the most time to recover. Try to perform an intense routine too soon after the intense exercise (which can take 4-10 days in some cases), and you will find that these muscles will not have yet properly recovered, leading to suboptimal performance. McGuff recommends that each major muscle group in rotation be subjected to a resistance exercise that takes the muscles to the point of exhaustion, using a small number of repetitions. It is at the point of near failure–where one can feel the lactic acid “burn”–that the glycolytic pathway and enzyme cascade is fully activated, leading to significant increases in muscular capacity after a requisite period of rest and recovery.
Because of the “order of recruitment”, performing high intensity exercise will also strengthen and adapt the slow twitch muscles, but the reverse is not true; sprinting will benefit your running and walking, but extensive walking will never make you a good runner. Of course, training benefits by specificity, so weight training is not sufficient to be a good athlete in any specific sport. A more appropriate routine for improving running capability is interval training, which includes periodic sprinting. This will push the muscles and metabolisim to adapt to a higher level of capability. Another advantage of shorter, more intense routines is that the chance of injury is reduced. Most injuries are overuse injuries or velocity injuries. By minimizing force and acceleration with the “slow cadence” technique, the risk of injury is minimized. The slow cadence method further ensures that muscles are truly worked and fatigued. This follows the hormetic principle of “constraint”, by using good form to focus the stress where it will provide the greatest benefit; moving weights at higher velocities (as seems to be common in most gyms) bypasses this “work” by relying upon the momentum of the weights, rather than the exertion of the muscles. In that sense, it is cheating, and the benefits will be suboptimal.
McGuff’s book is not the only program to advocate slow cadence, high intensity resistance training. Several other excellent books follow essentially the same recommendations, including Power of 10and Slow Burn, both of which provide very practical advice on exercise. While McGuff provides perhaps the best physiological explanation, he was certainly not the first to advocate high intensity training, which originated in the 1970s with the ideas of Arthur Jones, the inventor of Nautilis weight machines. Some trace the origins of slow cadence weight training back even further, to Gustav Zander. Zander developed similar equipment and exercises the 19th century.”