Peak Power Output and Muscle Metabolism in Sprinters
Usain Bolt, the enigmatic 21 year old sprinter from Jamaica, has taken Olympic track and field by storm being the first person in 24 years to win gold in both the 100 meter and the 200 meter sprints. His successes in both were definitive. He broke the 100 meter world record with a 9.69 (seconds). And his 200 meter was another world record at 19.30. In both races he was able to sprint at top speed for nearly the entire race, only losing a bit of speed near the end of the 200 meters.
In contrast to Bolt, Sonya Richards, the American favorite in the women’s 400 meters, ended up barely getting the bronze. She started out strong, way ahead in the first 200 meters sprinting at top speed. She still had a solid lead at the beginning of the last 100 meter stretch. But, then, suddenly, and dramatically, she ran “out of gas”. She struggled just to stay in third place. She didn’t have the energy to keep up, and she lost her chance at a gold medal.
It is rare for a runner to run out of gas at the end of a 100 or 200 meter dash. But, it happens a lot in the 400. Why the discrepancy? What does it say about the limits of human sprinting ability? And how long can a person, even an elite athlete, maintain maximal speed?
At the elite level, a 100 meter dash lasts about 10 seconds; a 200 meter lasts about 20 seconds; and the 400 takes about 1 minute. It is interesting to note that the 200 meter time is about double that of the 100 meter time, but the 400 meter is six times the 100 meter.
Insight into why it is that after about the 200 meter mark, or after about 20 seconds, the human body can’t keep up its maximal speed can be found at the cellular level: it comes down to ATP (the body’s preferred fuel source) production and the ATP turnover rate (Katz, 1986). The ATP turnover rate refers to your body’s speed-ability to produce ATP. But, to use ATP, the body first has to make it. There are three primary sources of ATP production. The fastest is the phosphocreatine (PCr) system that relies on creatine phosphate. This is used primarily for the shortest bouts of energy, like lifting a maximum weight for one repetition or a 20 meter dash. The second fastest is glycolysis that relies on sugar metabolism used for repetitions at a maximum power output, such as sprinting up to 200 meters. And the slowest is aerobic metabolism that relies on oxygen, primarily used at sub-maximal thresholds. Marathon runners rely primarily on aerobic metabolism.
According to a study by Bogdanis (1996), PCr is highly important to maximum power output for the first 10 seconds of sprinting, but declines rapidly thereafter. Peak power output, the highest level of power that a sprinter can produce, occurs at approximately 3 seconds (Bogdanis, 1998).
It has become widely accepted that PCr provides up to 25-30% of ATP production in a 30 second sprint, the rest coming primarily from glycolysis. In another study, also by Bognanis (1998), PCr stores were found to drop by nearly 60% after the first 10 seconds of sprinting. And after 20 total seconds of sprinting PCr levels have dropped to as low as 25% of the resting value. This means that in a sprint lasting longer than 10 seconds, there just isn’t enough PCr to do the job. But, power output doesn’t slow to a crawl.
Glycolysis generally works right along side the PCr system. Glycolysis uses glucose to form ATP. The glucose is stored in both the liver and in the muscle cells themselves. Glycolysis can operate in an anoxic (without oxygen) environment which makes it ideal for sustained maximal power output situations like a 100 to 200 meter dash because at that speed, the aerobic (oxygen) pathway can’t keep up. But, it has its drawbacks. The primary drawback of glycolysis is that when it is performing without oxygen the system backs up and produces an excess flood of lactic acid (Klapcinska) that builds up to high levels fairly quickly after the first 200 meters.
Aerobic metabolism is the way that our bodies generate ATP while we’re simply waking around, watching TV, or reading papers about metabolic reactions. It is slow, but it creates a large abundance of ATP. The trouble is that at top speed the aerobic pathway just isn’t fast enough to keep up. But, aerobic metabolism isn’t completely out to lunch in an all-out sprint. Remember that Usain Bolt and his competitors all ran the 200 meter sprint at close to full speed throughout the race, and it took most of them about 20 seconds to do it. They slowed down a bit near the end, but not much. If their PCr stores were used up, and their glycogen levels were down one would suspect that their speed would drop considerably as their ability to maintain maximum power output would be severely compromised. But, while their speed did drop near the end, it didn’t drop that dramatically (barely noticeable in fact). There must be some help coming from a different source. Bognanis (1998 ) found that some of that help may be coming from aerobic pathways, though more study is needed to examine why and how this happens.
But the aerobic pathway is too slow to help out for too long. For Sonya Richards, her all out effort for the first 200 meters of her 400 meter sprint left her completely lacking in power by the end of the race. She’d used up all her PCr, she’d depleted her glycogen, and the aerobic pathways just weren’t sufficient to replenish the amount of ATP she needed to win the gold. Her competitors, however, relied more on a combination of their aerobic pathways and glycolytic pathways in the first part of the race and saved their maximal power output for the end where they were able to overtake her.
Human beings are able to do amazing things when they train hard for them. Usain Bolt is a shining example of that. But there are limits to what our species can accomplish. After 10 to 20 seconds, it becomes exponentially harder to maintain the same average power output that one was able to achieve up to that point in an all out sprint. It just so happens that the fastest people in the world sprint the 200 meters in almost exactly 20 seconds, and the 100 meters in under 10 seconds. But, for 400 meter runners, an all out maximal sprint is not a good strategy. The body simply can’t maintain that pace for long. A lesson Sonya Richards will likely never forget.
References:
1. Bogdanis, G (1996). “Contribution of phosphocreatine and aerobic metabolism to energy supply during repeated sprint exercise”. Journal of applied physiology (1985) (8750-7587), 80 (3), p. 876.
2. Bogdanis, G (1998). “Power output and muscle metabolism during and following recovery from 10 and 20 s of maximal sprint exercise in humans”. Acta physiologica Scandinavica (0001-6772), 163 (3), p. 261.
3. Gaitanos, G (1993). “Human muscle metabolism during intermittent maximal exercise”. Journal of applied physiology (1985) (8750-7587), 75 (2), p. 712.
4. Katz, A (1986). “Muscle ATP turnover rate during isometric contraction in humans”. Journal of applied physiology (1985) (8750-7587), 60 (6), p. 1839.
5. Klapcinska, B (2001). “The effects of sprint (300 m) running on plasma lactate, uric acid, creatine kinase and lactate dehydrogenase in competitive hurdlers and untrained men”. Journal of sports medicine and physical fitness (0022-4707), 41 (3), p. 306.
Posted by saij
Posted by saij
Posted by saij
