OVERUSE MUSCLE
DAMAGE IN RUNNERS: ARE THE PERFORMANCE EFFECTS "ALL IN
THE HEAD?"
Scientists say muscle overuse changes RPE but
not lactate threshold .....
Exercise scientists have not been certain about the
effects of exercise-induced muscle damage (EIMD) on endurance running
performance. In mice forced to run downhill for extended periods
of time (an activity which creates mayhem in the murids' quads),
endurance capacity falls by about 65 percent during subsequent,
sub-maximal running efforts (1). In human runners, however, the
results have been quite different. Several different studies have
revealed that EIMD has no negative impact at all on key physiological
variables associated with endurance performance, including running
economy, energy metabolism during running, heart rate, and oxygen
consumption (2, 3, & 4). There is a failing in this research,
though: The human runners have not been asked to complete time trials
or actual competitions. Thus, it's possible that EIMD might have
little impact on the "usual suspects" (the variables
traditionally associated with performance) and yet still could hurt
competitive times.
To learn more
about the effects of EIMD on running performance, Sam Marcora and A.
Bosio from the School of Sport at the University of Wales-Bangor in the
United Kingdom recently worked with 30 adult runners (24 men and six
women). These athletes averaged 31 years of age, were fairly fit
(VO2max = 54.2), were moderately lean (13-percent body fat), and
trained four to five times each week with an average workout duration
of 48 minutes (5).
EIMD was
induced in half (15) of the runners via the completion of 100
"drop jumps." For each drop jump, a runner stood on a
35-centimeter-high bench (- 14 inches high), from which he/she dropped
to the floor with both feet, squatted to a 90-degree knee angle, and
then jumped in place as high as possible. After 10 such drop
jumps, a one-minute recovery was enforced, followed by nine
more sets of 10 drop jumps, with one-minute recoveries between
sets. Thus, the whole workout was 10 sets of 10 reps, with one-minute
recoveries. Research has shown that drop jumping can produce
significant EIMD, particularly in runners who have had little
experience with the maneuver (6).
No muscle
biopsies were performed after the drop-jumping, but four markers were
employed to detect the presence of underlying EIMD:
(A) Subjective
assessments of delayed-onset muscle soreness (DOMS) in the
buttocks, groin, thighs, hamstrings, calves, and shins,
(B) Blood
concentrations of creatine kinase, an enzyme which is usually elevated
when muscle problems occur,
(C) Mid-thigh
circumferences (an indicator of swelling of the quads and hams), and
(D)
Knee-extensor (quad) strength.
48 hours after
the drop jumps, running economy was measured as the runners cruised at
a velocity of 11.4 kilometers per hour (about 8:30 per mile
tempo). The runners also completed a 30-minute time trial during
which they ran as far as possible (these tests were also conducted 24
to 48 hours before the drop-jumping took place).
The 10 X 10
drop-jump workout produced increases in three of the four indirect
markers of EIMD. Two days after the drops, DOMS increased
11-fold, creatine-kinase concentration more than doubled, and
knee-extensor strength dropped by 12 percent (there was no significant
change in thigh girth). Nonetheless, EIMD was linked with no
change at all in heart rate, oxygen-consumption rate (and thus running
economy), or blood-lactate level during the 11.4-km per hour running.
The EIMD was
connected with a significant decrease in performance during the
30-minute time trial, however. Drop-jumped runners ran a
4-percent shorter distance during the time trial, compared with before
the drop-jumping (just 6631 vs. 6781 meters). Meanwhile, the 15
control runners (who had participated in no drop-jumping at all)
slightly increased the distance covered in 30 minutes (from 6545 up to
6652 meters).
What actually
caused this time-trial fall-off in the EIMD runners? Heart rate was not to blame, as
it stayed at 171 beats per minute during the trial, before and after
the muscle-macerating drop-jumping. A change in lactate threshold
was not the problem, either, since lactate levels were exactly the
same, before and after jumping. Rather, the difficulty was
related to an increase in perception of effort in the muscle-damaged
runners. RPE (rating of perceived effort) was actually the
same during the 30-minute time trial after
the bout of drop-jumping, even though time-trial pace was slower
(compared with the velocity of the time trial conducted before the drop
jumps). Basically, the EIMD runners compensated for an increased
sense of effort (caused by the EIMD) by adopting a slower running speed
during the second time trial, thus keeping RPE the same as before.
These results
coincide with findings from other research which reveal that athletes
estimate muscular force production based on their overall sense of
effort (7, 8, & 9). In studies in which one arm has incurred
muscle damage while the other has remained normal, subjects who are
asked to match with the damaged arm the force produced by the control
arm almost always underestimate force production. Similarly,
individuals asked to match with the control arm the force produced by
the damaged arm generally overestimate force production. This
means that athletes with EIMD perceive higher effort while producing a
given amount of force (compared with before damage occurred) - and
produce less force when perceived effort is held constant. Runners with EIMD, then,
will run at slower speeds than usual in order to avoid elevating
perceived effort, which may be tightly controlled by the brain.
How does the
brain know that EIMD has occurred? Obviously, the muscles can't
talk to the brain, but a chemical called interleukin-1B can increase in
response to muscle damage, and interleukin-1B can produce symptoms of
fatigue in humans. High concentrations of interleukin-1B have
been found in the brains of animals which have reduced running
performances associated with EIMD. Research also indicates that
blocking the activity of interleukin-1B decreases the harmful effect of
EIMD on performance, while artificially induced upswings in
interleukin-1B, even without actual muscle damage, produce drop-offs in
endurance running capacity which are similar to those associated with
EIMD (10).
The bottom
lines? When
you or the runners you coach experience significant drop-offs
in pace during training runs and/or competitions, the possibility
of underlying EIMD is significant.
This is especially true if RPE (perceived effort) is as high as usual
(or even higher). The cause of the EIMD may be overtraining
and/or a lack of running-specific strength. A solution is to
rest for an adequate period of time and then to engage in a systematic
program of running-specific strength training, which will minimize
muscle damage associated with subsequent, challenging workouts.
The other solution is to follow religiously the four principles of
muscle preservation:
(A) Fueling up
properly on a daily basis, taking in adequate quantities of
carbohydrate (about four grams of carbs per pound of body weight per
day) and total calories,
(B) Recovering
well between workouts, getting adequate sleep and taking at least one
day off from training each week,
(C) Avoiding
challenging sessions when muscles feel tight and sore, and
(D) Progressing
gradually with volume and intensity of training.
**********************************************************************
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References
(1) Brain Behav
Immunol, Vol. 19, pp. 445-452, 2005
(2)
International Journal of Sport Biomechanics, Vol. 7, pp. 125-137, 1991
(3) Journal of
Strength & Conditioning Research, Vol. 17, pp. 652-658, 2003
(4)
International Journal of Sports Medicine, Vol. 26, pp. 827-831, 2005
(5)
Scandinavian Journal of Medicine & Science in Sports, In Press,
2007
(6) European
Journal of Applied Physiology, Vol. 94, pp. 652-658, 2005
(7) Journal of
Physiology, Vol. 539, pp. 913-925, 2002
(8)
Experimental Brain Research, Vol. 149, pp. 141-150, 2003
(9) Exercise
& Sport Science Reviews, Vol. 33, pp. 98-104, 2005
(10) American
Journal of Physiology Regul Integr Comp Physiology, Vol. 29 (5), pp.
1344-1348, 2006
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