Adaptations to anaerobic training

In muscular activities that require near-maximal force production, such as sprinting, cyclilng, and swimming, much of the energy needs are met by the ATP-phosphocreatine(PCr) system and the anaerobic breakdown of muscle glycogen(glycolysis).

Changes in anaerobic power and anaerobic capacity

Exercise scientists have had difficulty agreeing on an appropriate laboratory or field test of anaerobic power. Unlike the situation with aerobic power, for which VO₂max is generally agreed to be the gold standard measurement, no single test adequately measures anaerobic power. Most research has been conducted through use of three different tests of either or both anaerobic power and anaerobic capacity: the Wingate anaerobic test, the critical power test, and the maximal accumulated oxygen deficit test. Of these three, the Wingate test has been the most widely used.

With the Wingate anaerobic test, the subject pedals a cycle ergometer at maximal speed for 30s against a high braking force. The braking force is determined by the person’s weight, sex, age, and level of training. Power output can be determined instantaneously throughtout the 30s test but is generally averaged over 3 to 5s intervals. The peak power output is the highest mechanical power achieved at any stage in the test; it is generally achieved during the first 5 to 10s and is considered an index of anaerobic power. The mean power output is computed as the average power output over the total 30s period, and one obtains total work simply by multiplying the mean power output by 30s. Mean power output and total work have both been used as indexes of anaerobic capacity.

With anaerobic training, such as sprint training on the track or on a cycle ergometer, there are increases in both peak anaerobic power and anaerobic capacity. However, results have ranged widely across studies, from those that showed only minimal increases to those showing increases of up to 25%.

Adaptations in muscle with anaerobic training

With anaerobic training, which includes sprint training and resistance training, there are changes in skeletal muscle that specifically reflect muscle fiber recruitment for these types of activities. At higher intensities, type II muscle fibers are recruited to a greater extent, but not exclusively, because type I fibers continue to be recruited. Overall, sprint and resistance activities use the type II muscle fibers significantly more than do aerobic activities. Consequently, both type IIa and type IIx muscle fibers undergo an increase in their cross-sectional areas. The cross-sectional area of type I fibers also is increased but usually to a lesser extent. Furthermore, with sprint training there appears to be a reduction in the percentage of type I fibers and an increase in the percentage of type II fibers, with the greatest change in type IIa fibers. In two of these studies, in which subjects performed 15s or 15s and 30s all-out sprints, the type I percentage decreased from 57% to 48% and type IIa increased from 32% to 38%.  This shift of type I to type II fibers usually is not seen with resistance training.

Adaptations in the energy systems

Just as aerobic training produces changes in the aerobic energy system, anaerobic training alters the ATP-PCr and anaerobic glycolytic energy systems. These changes are not as obvious or predictable as those that result from endurance training, but they do improve performance in anaerobic activities.

Adaptations in the ATP-PCr system

Activities that emphasize maximal muscle force production, such as sprinting and weightlifting events, rely most heavily on the ATP-PCr system for energy. Maximal effort lasting less than about 6s places the greatest demands on the breakdown and resynthesis of ATP and PCr. Costill and coworkers reported their findings from a study of resistance training and its effects on the ATP-PCr system. Their participants trained by performing maximal knee extensions. One leg was trained using 6s maximal work bouts that were repeated 10 times. This type of training preferentially stressed the ATP-PCr energy system. The other leg was trained with repeated 30s maximal bouts, which instead preferentially stressed the glycolitic system.

The two forms of training produced the same muscular strength gains(14%) and the same resistance to fatique. As seen in the figure below, the activities of the anaerobic muscle enzymes creatine kinase and myokinase increased as a result of the 30s training bouts but were almost unchanged in the leg trained with repeated 6s maximal efforts. This finding leads us to conclude that maximal sprint bouts(6s) might improve muscular strength but contribute little to the mechanisms responsible for ATP and PCr breakdown. Data have been published, however, that show improvement in ATP-PCr enzyme activities with training bouts lasting only 5s.

Regardless of the conflicting results, these studies suggest that the major value of training bouts that last only a few seconds(sprints) is the development of muscular strength. Such strength gains enable the individual to perform a given task with less effort, which reduces the risk of fatique. Whether these changes allow the muscle to perform more anaerobic work remains unanswered, although a 60s sprint-fatique test suggests that short sprint-type anaerobic training does not enhance anaerobic endurance.

Adaptations in the glycolytic system

Anaerobic training(30s bouts) increases the activites of several key glycolytic enzymes. The most frequently studied glycolytic enzymes are phosphorylase, phosphofructokinase(PFK), and lactate dehydrogenase. The activities of these three enzymes increased 10% to 25% with repeated 30s training bouts but changed little with short(6s) bouts that stress primarily the ATP-PCr system. In a more recent study, 30s maximal all-out sprints significantly increased hexokinase(56%) and PFK(49%) but not total phosphorylase activity or lactate dehydrogenase.

Because both PFK and phosphorylase are essential to the anaerobic yield of ATP, such training might enhance glycolytic capacity and allow the muscle to develop greater tension for a longer period of time. However, as seen in the figure below, this conclusion is not supported by results of a 60s sprint performance test, in which the subjects performed maximal knee extension and flexion. Power output and the rate of fatique(shown by a decrease in power production) were affected to the same degree after sprint training with either 6 to 30s training bouts. Thus, we must conclude that performance gains with these forms of training result from improvements in strength rather than improvements in the anaerobic yield of ATP.