Part 2 – Speed of Contraction
Muscle contractility, which exerts the greatest influence on athletic performance, is composed of three primary factors – speed of contraction, strength, and fatigue resistance. We will need to examine all three of these factors in detail so as to gain an understanding of the best way to train in order to improve them. Let’s start with speed of contraction.
The speed at which your muscle fibers contract is the most significant of the three characteristics. Speed of contraction explains why Nolan Ryan could throw a baseball so fast or why Carl Lewis could sprint the way he could. Both of these guys had amazingly fast contracting muscle fibers compared to the rest of us.
Muscle fiber contraction speed is determined by individual muscle fiber characteristics. Though we know that fast twitch fibers are much faster contracting than slow twitch fibers it is not as simple as saying that really fast people have mostly fast twitch fibers. Like all other human characteristics there is a range of contraction speeds across the human population. Some people are born with fibers that contract much faster than the average. For example, some people have slow twitch fibers that contract as fast as the average person’s fast twitch fibers. These people would have an inborn genetic advantage in endurance events. Further, scientists have classified muscle fibers into at least 6 different types, with various grades of fastness and slowness amongst the fibers. Unfortunately, the composition of your muscles – the % of slow, medium, and fast fibers that compose your whole muscle – is genetically determined and does not change with training.(1) All the training in the world won’t convert your slow twitch fibers into fast twitch fibers.
Additionally, speed of contraction does not change significantly with training. It appears to be one of the inborn characteristics that really doesn’t seem to improve with training. For example, when world class sprinter Leroy Burrell was in high school his fastest time in the 100 meters was 10.43 seconds. As an adult he set the world record with a 9.85 second time, an increase of only .58 seconds or less than a 6% improvement.(2) That may be a lot in the sprinting world, but we routinely see much greater improvements in distance running than 6%.
Even with years of physical, mental, and emotional maturation plus years of additional training Leroy was only able to increase his 100 meter sprint about ½ second. I suspect most of Leroy’s improvement came from an increase in initial acceleration out of the blocks and from the ability to maintain maximum velocity for just a little bit longer. I would be very surprised if the top speed he achieved changed. Indeed, sprint research indicates that most improvements in sprint performance come about as a result of the sprinter being able to accelerate to top speed faster and from being able to maintain top speed for a longer period of time. If speed of contraction did improve with training we would expect to see increases in the top speed a runner can attain, and hence, greater improvements than ½ second in the 100m sprint.
The important thing to understand for our discussion is that once you are firing a whole muscle at the fastest rate it is capable of reaching, that’s it; you are moving as fast as you are capable of, you are at your top speed.
Any reasonably fit adult can sprint at a pace that elicits their maximum rate of contraction. In other words, a fit adult is strong enough to accelerate to the top speed of their muscles. Increasing the strength of a muscle will not generally increase the maximum pace that you can attain, because the fibers are not capable of increasing the rate at which they can contract. A fixed maximum contraction rate, more than anything else, explains why all the training in the world won’t convert an individual with normal muscle fiber contraction speed into an elite runner.
Even Arthur Lydiard, who so widely promoted high volume training as the best method for distance running success, recognized the importance and unchanging nature of speed of contraction.
“As far as I’m concerned, this sprint test is the best way to judge your potential. Your basic speed – not your build, leg length, or weight – should determine what distance you run. If you can’t run the 200 faster than 26 seconds, for instance, forget all about half-miling. All the training in the world won’t make you a champion at it…If you can’t run a 400 in 51 seconds, you can’t run an 800 in 1:50. And if you can’t do that, you don’t have a chance in today’s racing circles”
– Arthur Lydiard and Garth Gilmore, Running the Lydiard Way
In summary, muscle contractility is the primary limiting factor in performance. Muscle contractility is composed of speed of contraction, strength, and fatigue resistance. If you can improve any of these characteristics, your performance will improve. Unfortunately, speed of contraction, which is the most important of the characteristics, is genetically determined and changes little with training.
1. McArdle, Katch, Katch (1996). Exercise Physiology, 314
2. Dintiman, Ward, Tellez (1998). Sports Speed, 2nd Edition, vi