Speaking generally, your skeletal muscle fibers fall into two broad categories, Type I and Type II. Type I fibers commonly are called “slow-twitch,” Type II fibers usually are referred to as “fast-twitch,” and the colloquial monikers are pretty appropriate: the maximum contraction velocity of a slow-twitch fiber is significantly slower than that of a fast-twitch fiber, although both produce about the same amount of force per contraction. Relying primarily on aerobic metabolism to fire, slow-twitch fibers use oxygen more efficiently than fast-twitch fibers, which depend heavily upon anaerobic metabolism. Accordingly, fast-twitch fibers are better at generating short bursts of strength or speed while slow-twitch fibers are optimized for continuous contractions repeated over a long period of time.
While all humans possess some combination of slow-twitch and fast-twitch fibers, those primed for long distance endurance activities, such as marathon running and stage-race cycling, possess greater proportions of slow-twitch fibers. Athletes that excel at fast, high-intensity activities such as sprinting and weight-lifting generally possess greater proportions of fast-twitch fibers. While I am unaware of any studies linking relative fiber concentration to other genetic factors, several studies suggest that training can be used to transform fibers from one type to the other.
Though they are also capable of being classified using even more specific terms, canine skeletal muscles generally fall into the same fast-twitch/slow-twitch categories as human muscles.
This is an important fact to keep in mind when creating and carrying out your dog’s exercise program. To optimize your dog’s fitness and ensure that she reaps the greatest possible health, wellness, and longevity benefits from it, be sure to develop her skeletal muscles in a comprehensive and well-rounded way. In other words, be sure to incorporate training designed to grow and strengthen both fast-twitch and slow-twitch fibers.
A few quick words on how to do that:
To develop slow-twitch fibers, focus on less intense but longer duration activities such as walking and trotting. The name of the game here is progression through increased duration and not through increased intensity. So if your dog breaks into a run or starts to pant heavily, you need to scale back the intensity to ensure that the appropriate metabolic process is fueling her activity (and to avoid overheating). Consult a veterinarian before beginning to ensure that you’re starting with an appropriate duration.
To develop fast-twitch fibers, focus on jumping and sprinting activities such as short distance fetch games and obstacle-based activities which require repeated jumping movements. Progression here should be viewed in terms of increased speed and each go-round shouldn’t last more than 30-45 seconds, with appropriate rest intervals separating work intervals. Again, always consult a vet before starting a new workout program.
To optimize your dog’s fitness, effort should be made to draw from both types of workouts.
Have a great Wednesday!
– Coach Dan