Gabe Mirkin, M.D.
When you exercise for a long time, your muscles start to
burn and feel sore, which forces you to slow down. You call this
fatigue and tiredness, but a recent study from Japan shows that
muscle fatigue is caused by damage to the muscle itself
(Medicine & Science in Sports & Exercise, July 2005). This also
explains why exercising long and hard enough to feel the burn for
an extended period leaves your muscles sore for one or more
days afterwards. Athletes call this Delayed-Onset Muscle
Soreness (DOMS) and they learn that they have to have this
next-day soreness to improve for competition.
Running is much more fatiguing than cycling. When you
run, your heel hits the ground and stops your leg from moving.
This sudden stopping with each foot strike stretches your
contracting muscles and tears them to cause a lot of muscle
damage. It’s called eccentric contractions of muscle and occurs
with far less force in cycling. You pedal with a smooth rotary
motion and do not stop suddenly. The eccentric contractions
during running cause a high degree of muscle injuries, limit how
far person can run fast, and require far more rest days or easy
days than cyclists use in their training programs.
Since muscle fatigue during endurance competitions is
caused by muscle damage, anything that strengthens muscles
will improve performance in endurance events. The only way to
make a muscle stronger is to damage the muscle with hard
exercise, feel sore on the next day, exercise more easily on as
many days as it takes for the soreness to go away, and then
exercise vigorously again. Athletes in competitive sports must
exercise at a reduced intensity on the days that their muscles
feel sore. This makes muscles more fibrous and resistant to
injury so that muscles can withstand greater forces when athletes
exercise on their hard days.
May 1, 2006