Starting Strength

of responding to the demands of increased peak blood pressure. The tendons thicken to better transmit force, and the ligaments thicken and tighten to hold the joints together under the load. The skin under the bar gets thicker, the eyeballs get used to bugging out, and new words are learned that express the emotions accompanying success or failure with a new PR squat. But the primary adaptation is increased force production.
    On the other hand, a heavy set of 20 reps is an entirely different experience, one of the most demanding in sports conditioning. A set of 20 squats can usually be done with a weight previously assumed to be a 10RM, given the correct mental preparation and a certain suicidal desire to either grow or die. The demands of a 20RM, and therefore the adaptation to it, are completely different. A 20RM is done with about 80% of the weight of a 1RM, and even the last rep is not really heavy, in terms of the amount of force necessary to squat it. The hard part of a set of 20 is that the last 5 reps are done in a state resembling a hellish nightmare: making yourself squat another rep with the pain from the falling muscle pH, an inability to catch your breath, and the inability of your heart to beat any faster than it already is. The demands of a 20RM involve continued muscle contraction under circumstances of increasing oxygen debt and metabolic depletion.
    In response to this type of stress, the body gets better at responding to the high metabolic demand that is created. Systemic adaptations are primarily cardiovascular in nature, since the main source of stress involves managing blood flow and oxygen supply during and after the set. The heart gets better at pumping blood under a load, the vessels expand and become more numerous, and the lungs get better at oxygenating the blood – although not in the same way that a runner’s lungs do. The main muscular adaptations are those that support local metabolism during the effort. Glycolytic capacity increases. The contractile part of the muscle tissue gets better at working under the acidic conditions produced by the stress of the long work set. Psychologically, 20RM work is very hard, due to the pain, and lifters who are good at it develop the ability to displace themselves from the situation during the set. Or they just get very tough.

    Figure 8-3. Sets of 5 reps are optimal for learning barbell exercises. It is apparent from electromyography (EMG, a recording of neuromuscular electrical activity, top) and force plate data (a measure of muscular force generated, bottom) that there is a progressive loss of motor coordination as reps increase. In reps 1–5, the muscle is firing in a coordinated manner, with tight, uniform EMG waves and consistent force production. By reps 10–14, there is a loss of motor coordination, with erratic EMG wave and force continuity. By reps 25–29, EMG activity is highly random and force production has deteriorated. Using more than 5 reps per set during the learning phase of a new exercise will usually make correct technique harder to reproduce and master. Note that the peak level of force production is the same on rep 1 and rep 20, although control has begun to degrade; a 20-rep set is not really “heavy,” but it sure is long and hard.

    Figure 8-4. The metabolic speedometer. How hard and how long we exercise directly affects which metabolic pathways our bodies primarily use to fuel the activity. All physical activity lies along a continuum, from rest to all-out maximal effort. All activities are powered by the ATP already present in the muscle, and all bioenergetic activity acts to replenish these stores. Low-intensity exercise depends on cardiopulmonary delivery and muscular uptake of oxygen, the ready availability of which enables the body to use aerobic pathways and fatty acids as substrate. These aerobic processes take place inside the mitochondria within the muscle cells. As activity levels and energy requirements increase, the ability of oxidative metabolism to meet the increased demand for ATP is exceeded. Weight training and other forms of high-intensity training exist at the anaerobic end of the continuum, using substrate that does not require added O2. The diagram above represents the relationships between the energy substrates and the metabolic pathways in which they are used in different types of exercise. With the exception of short-duration all-out maximal efforts, no activity uses only one metabolic pathway,