What are the strength characteristics of sprinters?
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What are the strength characteristics of sprinters?
One of the ways in which we can investigate the effects of certain types of athletic training is to compare the performances of two groups of subjects, one that performs a particular training method and the other that does not. However, one of the main problems with this approach is that athletes often perform several types of training. So if we compare athletes with non-athletes, it is difficult to see which training method has led to the differences we observe. This very interesting study addressed that problem for sprinting by comparing the performances of sprinters with the performances of weight-trained non-sprinters. They even managed to obtain groups with similar 1RM back squats. In this article, Chris Beardsley (@SandCResearch) investigates what they found.
The study: Physical Performance Differences Between Weight- Trained Sprinters and Weight Trainers, by Blazevich and Jenkins, in Journal of Science and Medicine in Sport, 1997
(Too much detail? Skip to the practical implications)
What did the researchers do?
The researchers wanted to compare the isokinetic hip flexion and extension torques of well-trained sprint athletes who regularly used low-velocity, high-force resistance training in addition to their sprint training, with non-sprinters who also regularly used low-velocity, high-force resistance training but who did not perform sprints. The idea was to see what effect the sprinting training would have on sprint ability and on torque production at different speeds. So they recruited 11 male sprinters (100m and 200m) and 8 male weight-trained athletes who were not currently performing sprint training. All of the subjects had a minimum of 2 years of weight training experience but none of the subjects performed high-velocity resistance training. The subjects performed five sets of tests, which were:
- 20m accelerating sprint from stationary start
- 20m flying sprint with 50 m acceleration distance
- 1RM back squat
- Isokinetic hip flexion at 60, 270 and 480 degrees/s
- Isokinetic hip extension at 60, 270 and 480 degrees/s
Sprinting and squat performances
Unsurprisingly, the researchers found that the sprinters were much better at both the 20m sprint and the 20m flying sprint, as the chart of their times below demonstrates. The differences between sprinters and non-sprinters were significant.
Hopefully, someone will one-day do the same kind of study comparing sprinters who use Olympic weight-lifting as part of their routine and Olympic weightlifters. Then we can all stop talking about whether that elusive study in Mexico City that supposedly recorded the sprint performances of Olympic weightlifters really happened or not. Also, it is important to note that there was no statistical difference between the maximum squat performance of the two groups, which is useful, as it allows us to compare them during the isokinetic tests on an even footing.
Isokinetic hip extension torque at different speeds
The researchers observed that in both sprinters and non-sprinters, the hip extension torque exerted during the isokinetic tests decreased with increasing velocity, as we would expect from the force-velocity relationship. However, what is most interesting is that the sprinters display a trend towards a greater ability to produce hip extension torque at higher speeds, as we can see in the chart below.
There is quite a lot going on that needs to be discussed here. First of all, it is important to note that none of the differences were significant. Therefore, we are just looking at trends. That being said, other studies have found that sprinters display higher forces at higher velocities than other athletes. For example, Taylor (1991), found that sprinters displayed higher knee extension torque than endurance athletes. This result may have been affected by differences in the amounts of resistance training performed by the athletes, however. Similarly, as another example, Alexander (1990) found that sprinters displayed greater differences from non-athletic controls when measuring higher velocity isokinetic torque of the hip and knee.
In our study, Blazevich and Jenkins found that peak isokinetic hip extension torque at 480 degree/s was 7.8% greater in the sprinters than in the non-sprinters. However, they also found that the non-sprinters were actually 5.5% stronger at 60 degree/s. Finally, they found that both groups produced similar torque at 270 degree/s, which was the middle speed. One explanation for this trend is that the sprinters may have developed a velocity-specific strength as a result of their sprint training. An alternative explanation would be that they were genetically more capable of producing higher forces at higher speeds, perhaps because of an innate greater proportion of fast twitch fibers. Unfortunately, this study does not help us determine which of those possibilities is more likely.
Isokinetic hip flexion torque at different speeds
The researchers again observed that in both sprinters and non-sprinters, the hip flexion torque exerted during the isokinetic tests decreased with increasing velocity, as we would expect from the force-velocity relationship. However, the researchers also found that the sprinters displayed a greater ability to produce hip flexion torque at higher speeds. This is shown in the chart below. And in this case, the difference between sprinters and non-sprinters was significant at 480 degrees/s.
As was the case for hip extension torque, the researchers found that peak isokinetic hip flexion torque at 480 degree/s was 38.4% greater in the sprinters than in the non-sprinters but the non-sprinters was actually 2.6% stronger at 60 degree/s. However, unlike hip extension torque, the sprinters were also 12.6% stronger than the non-sprinters at the intermediate velocity of 270 degrees/s. Whether this reflects a more velocity-specific role of the hip extensors over that of the hip flexors is not known.
Differences between hip extension and hip flexion torques
What may have been obscured by the above charts is the speed at which the force declines with increasing velocity. In the following chart, we can see the decreases of both hip extension and hip flexion torque with increasing velocity from 60 degrees/s through to 480 degrees/s for both sprinters and non-sprinters.
As you can see from the chart, the decrease in hip flexion torque appears to be much greater than that of hip extension torque. However, it is interesting to note that Pontaga (2003) also investigated the ratio of isokinetic hip flexion to hip extension torques at difference angular velocities when testing in dynamometer. Pontaga found that the ratio could be very different depending on whether the measurement was taken in a high degree of hip flexion or at a very low degree of hip flexion. In some degrees of hip flexion, Pontaga found that the ratio increased with increasing speed, while in others the ratio decreased. Specifically, in high degrees of hip flexion, Pontaga found that increasing speed led to increased hip-flexion-to-hip extension torque ratios. In low degrees of hip flexion, he found that increasing speed led to decreased ratios but the effect was not as marked.
Differences between the angle at which peak hip flexion or extension torque occurs
The angles at which peak torque was reached by the sprinters and non-sprinters were only significantly different for hip flexion at 270 degrees/s and 480 degrees/s, as can be seen from the following chart. There were no significant differences in respect of the angles at which peak hip extension torque occurred.
For both the isokinetic speeds of 270 and 480 degrees/s of hip flexion, the sprinters displayed a greater hip angle for peak torque production. Exactly why this occurs is not clear but it may relate to the importance of a particular hip angle during the movement of sprinting, or simply to the nature of isokinetic dynamometry training at faster speeds.
Time to peak hip extension torque at different speeds
The following chart shows the time to peak hip extension and flexion torques at 270 and 480 degrees/s. All variances apart from the peak hip extension torque at 480 degrees/s were significantly higher in sprinters than in non-sprinters. It is noteworthy that the time taken to reach peak hip flexion torque at 480 degrees/s is very much longer than the other variables measured and particularly since this measure of torque was also much lower in torque output than the other variables.
This demonstrates quite clearly that sprinters have a greater rate of force development than non-sprinters, even when both sprinters and non-sprinters perform heavy resistance training. This may be because of the sprint training or it may be because of genetic make-up. Additionally, it shows that the hip extensors are more effective at higher movement velocities than the hip flexors.
What did the researchers conclude?
The researchers concluded that sprint athletes perform best at isokinetic tests that require high-speed strength (i.e. sprinting velocity and moderate- and high-speed isokinetic hip strength tests). The researchers suggest that this difference might arise from increased rate coding and recruitment of motor units and either selective recruitment of fast-twitch fibers or greater fast-twitch fiber percentage.
What are the limitations?
The researchers note that their study was limited insofar as it is not possible to assess whether the differences are due to genetic predisposition or changes as a result of training methods. There is a lot going on in this study and many of the findings were non-significant, which is quite annoying as it is a really interesting study. So I have to say that I think it was limited by a small sample size. I really wish they had found a way to increase their number of subjects so that the statistics could have had a better chance of finding some differences in the peak isokinetic torque measures. I also wish they had taken isometric torque measurements at different ranges of motion. It would be very interesting to see how the sprinters and non-sprinters differed in respect of their ability to produce isometric torque at different ranges of motion.
What are the key points?
From this study, we can gather the following:
- Sprinters perform significantly better at sprinting tasks than weight-trained non-sprinters with similar 1RM back squats. This sounds obvious but remember it next time you read an article about how to sprint faster.
- Sprinters have a higher rate of force development than non-sprinters even when they have similar 1RM back squats.
- In both sprinters and non-sprinters, isokinetic hip flexion torque decreases faster with increasing velocity than isokinetic hip extension torque.
- Sprinters display a different angle of peak isokinetic hip flexion torque than non-sprinters. This may relate to the importance of a particular hip angle during sprinting.
- Sprinters display a trend towards greater hip flexion and hip extension torques at higher isokinetic velocities, although these findings in this study were mainly non-significant (the only significant difference between sprinters and non-sprinters was hip flexion with 480 degrees/s).
What are the practical implications?
Since sprinters were better at sprinting than weight lifters who had similar back squat performances, it seems very likely that sprinting is essential for improving sprint performance.
Sprinters display a different angle of peak isokinetic hip flexion torque than non-sprinters. This may imply that sprinting involves the production of peak torque at a different joint angle from the most popular lower body resistance training exercises.
Sprinting or other actions requiring very fast stretch-shortening cycle movements, such as drop jumps, may be useful for developing rate of force development in athletes of all sports.
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