Fast Twitch, Slow Twitch

What makes you a sprinter vs. a distance swimmer?  Many scientists and coaches say that the primary factor for determining whether a swimmer is a better distance swimmer or a sprinter lies in the muscles of each athlete.  To put it simply, people inherently have either more fast twitch or more slow twitch muscles.  And, depending on the type of muscle that predominates, a swimmer will either be better at endurance events or quick, speed events.  

Fast Twitch vs. Slow Twitch.  A swimmer’s endurance and speed are largely determined by the muscles’ ability to produce force and energy.  Differences in performance can be related to the characteristics that make up your arm and leg muscles.  There are two types of muscles: slow twitch and fast twitch.  Slow twitch muscle fibers provide good aerobic endurance and are typically utilized during low-intensity endurance events, like the 500 freestyle.  Fast twitch muscles on the other hand, are used during short, fast (primarily sprint) races like the 50 and 100 freestyle.  Fast twitch muscles develop more force than slow twitch, but they fatigue easier and quicker than slow twitch.  When swimmers are training with slow, low-intensity swimming, slow twitch muscles fuel most of their muscle force.  As the muscles tense with increased intensity, fast twitch muscles start performing.

Workouts.  This slow twitch versus fast twitch comparison is important when considering the amount and intensity of workouts in any given training season.  We can make the correlation that training done at a slow pace will emphasize the use of slow twitch muscle fibers and downplay the fast-twitch muscle fibers.  The long slow training which emphasizes slow twitch muscle buildup, does not prepare the swimmer properly for competition, where maximal force must be exerted by both fast twitch and slow twitch muscle fibers.

Some swimmers have a higher composition of slow twitch fibers in their body, and these swimmers are better suited for long endurance events whereas those with fast twitch muscles are better suited for the sprints.  It is generally accepted that one’s preponderance of slow twitch vs. fast twitch muscles cannot drastically change with a different training regime.  Most studies seem to indicate that the composition of muscles remains fixed and unaffected by training, and the composition is mostly a genetic trait of each swimmer.  In other words, you are stuck, for the most part, with the muscle make-up that your parents gave you at birth. 

Muscle biopsies can ultimately be performed to determine each swimmer’s muscle characteristics, but it is important to remember that the slow twitch and fast twitch fiber makeup does not directly correlate to successful competitive swimming.  This means that there is no ideal muscle make-up that will ensure victory.  However, looking at muscle fiber energy use can provide important information for training.

The Bottom Line.  Over time, with practice and competition, a swimmer should be able to figure out if he or she is a distance or sprint swimmer.  Generally, a swimmer will be better at one or another, which is likely due at least in part to a swimmer's inherited muscle makeup.  Swimmers should choose their specialties accordingly.

Despite that, swimmers must be sure to perform at least some training that works both types of muscle groups with a concentration on training at or near racing speeds to work the fast twitch muscles for competition.  There can be a tendency for coaches to "pound out" long slow yardage for the majority of the season and only train sprints when nearing competition.   This can result in poor race results as swimmers can't 'sprint into the finish or finish hard enough to win a tight race.  We suggest that to best utilize the slow and fast twitch muscles training should be done both at long slow intensity and fast, sprint intensity.