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The Science of Performance |
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Power Runningsm Part 5: Muscular Fatigue Have you ever tried to run an all-out sprint for 400 meters? Can’t do it, can you? Despite our best efforts, most of us can only sustain our maximum speed for just a few brief seconds. Even the world’s best sprinters can maintain their maximum speed for only 20 – 40 seconds. Why is that? Additionally, have you ever noticed that the pace you can maintain for 5k is significantly faster than the pace you can maintain for 10k? For example, while you might run a 5k at a 6:00 minutes per mile pace, you would run a 10k at the slower pace of 6:15 minutes per mile. If you tried to run a 10k at your 5k pace of 6:00 minutes per mile, you would fatigue during the later miles of the race and your pace would slow quite dramatically. In all probability, your pace over the last 2 – 3 miles of the 10k race would be so slow that your overall pace would be less than the 6:15 minute per mile you were capable of. The effect of fatigue on your pace is quite pronounced, hence the common recommendation that you run a “negative split” during your races (i.e. running the second half of a race slightly faster than the first half). It is a characteristic of our muscles that they can generate a set amount of force for a finite amount of time. It is also a well observed fact that the longer the distance to be run, the slower the pace will be. Each increase in distance will be accompanied by a decrease in pace. We call this effect muscular fatigue and it is the subject of our discussion today. What causes fatigue? Physiologists have identified several contributing factors of fatigue. Most any running book or magazine will identify factors such as ambient temperature, core body temperature, dehydration, muscle glycogen levels and others. As it turns out, all these factors are related to metabolic fitness, and do not explain muscular fatigue. Unfortunately, not much successful research has been done to ascertain the exact causes of muscular fatigue. There are a few things we do know though. First, muscle fiber is subjected to considerable mechanical stress during exercise, especially during unaccustomed exercise, periods of high force, or significant eccentric contractions (muscle lengthening). This stress results in the fibers not being able to contract as powerfully as they could previously. For as yet unidentified reasons, the mechanical stress weakens the fibers, causing a decrease in power. Second, muscle fibers are traumatized during exercise, and suffer significant levels of micro-trauma. In 1983 Robert Hikida and his associates at Ohio University pointed an electron microscope at the muscle fibers of marathon runners. Their findings were very surprising. In nearly all the samples, there was evidence of ruptured fibers and inflammation. Additionally, many of the substances normally confined to the inside of the muscle cell were found outside, in the fluids that surround the muscle. Even red and white blood cells were found outside the blood vessels. The researchers also observed derangements in the contractile filaments.1 Perhaps more importantly, the damage was found before the runners competed in the marathon! The runners had experienced significant levels of muscle damage even before they lined up to run the marathon. You could say that these marathon runners started the race already fatigued, to some extent anyway Micro-trauma impairs the ability of the muscle to contract, contributing to overall muscular fatigue. Certainly some of the symptoms noted above show up post exercise, but micro-trauma occurs during exercise, contributing to muscle fatigue during exercise. The lesson here is that runners experience both metabolic and muscular fatigue during exercise. For as yet not fully understood reasons, muscle fibers fatigue during exercise; mechanical stress is probably the greatest cause of muscle fatigue, but micro-trauma can also occur during exercise and would contribute to fatigue. Importantly, the fatigue experienced by muscle fibers is in addition to the fatigue associated with metabolic fitness, and can require a significantly longer period of time to recover from than the transient effects of metabolic fatigue. Minimizing muscular fatigue How should you train to minimize the effects of muscle fatigue on performance? Like all physical attributes, the body responds only when a sufficient stimulus is presented. Strength training, speed work, and specificity of training intensity and distance all contribute to enhancing muscular endurance and resistance to fatigue. The previously recommended weekly speed workouts and weight training sessions will not just increase your strength, but will also make your muscles more resistance to fatigue caused by mechanical stress and micro-trauma. Additionally, by conducting some of your training specifically at the pace, distance, and environment at which you are scheduled to race, you will also increase your resistance to muscular fatigue. The combination of these three types of workouts will make your muscles as immune to fatigue as is possible. Till next time keep on running. References: 1. Costill, D (1986). Inside Running: Basics of Sports Physiology, 125 - 143
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