Possible Mechanisms underlying the decrease in
performance associated with Overtraining Syndrome (OTS)
David Bishop, Australia |
|
This presentation was made during the 2004 Pre-Olympic Congress in
Thessaloniki, Greece, August 6-11th. The full text of the article is
currently under review and will be available in the near future.
David Bishop, J.R. Grove & S. Russell
School of Human Movement and Exercise Science, The University of Western
Australia, Australia
Introduction
While high-intensity interval training can improve performance [1] it
is also well known that performing large amounts of high-intensity training
may result in the athlete developing overtraining syndrome (OTS) [2].
To date, most research has been directed towards determining indicators
of OTS in an effort to predict and therefore prevent overtraining in
athletes. However, less attention has been given to determining why
overtraining limits performance. Possible mechanisms that can limit
performance include an increase in metabolic end products such as lactate
and hydrogen ions, muscle glycogen depletion, earlier attainment of
VO2peak and increased “sensation” of fatigue, among others.
The purpose of this study was to examine possible mechanisms underlying
the performance limiting effects associated with OTS.
Methods
Twelve moderately-trained males performed a graded exercise test (GXT)
to determine VO2peak and lactate threshold (LT). Time-to-fatigue (TTF)
at 20% of the difference between VO2peak and LT was also assessed. Following
these tests, subjects were randomly assigned to either a control (N=6)
or training group (N=6). Those assigned to the training group were required
to complete two high-intensity interval-training sessions per day, seven
days per week for up to 3 weeks. Training consisted of up to 14, two-minute
intervals performed at 150% of LT with one-minute rest. A TTF test replaced
one of the training sessions every second day. Training continued until
TTF decreased to 75% of the initial TTF test. Those assigned to the
control group performed a TTF test every second day. Within 48 h of
this final TTF test, a GXT was performed by the subject and their matched
pair in the control group. Capillary blood was sampled and RPE determined
at 75% of initial TTF and at TTF for all tests. VO2 was also determined
during all TTF tests.
Results
TTF was significantly different between the training and control groups
on the final TTF test (P< 0.05). VO2peak (L.min-1) was not significantly
different for either the training or control group pre or post training
(P >0.05). For the training group, there was no significant difference
between blood lactate concentration measured at 75% of TTF on day one
and blood lactate concentration measured at fatigue on the final TTF
test (P > 0.05). There were also no significant differences in VO2
(L.min-1) on day one at 75% fatigue, day one at fatigue or at fatigue
on the final TTF test for either group. Final ratings of perceived exertion
for the training group did not differ significantly from those measured
on day one at TTF (P > 0.05).
Discussion / Conclusions
The high-intensity interval-training protocol resulted
in significant performance decrements as assessed by the TTF test. These
results are comparable to those of Fry et al. [3] who showed decreased
time to exhaustion in five well-trained men after a period of intense
training performed twice per day for ten days. Earlier accumulation of
maximal levels of blood lactate, earlier attainment of VO2peak and earlier
sensation of fatigue did not seem to be the mechanisms underlying the
performance decrement associated with this training protocol. There is
little data reporting the effects of OTS on physiological and psychological
responses at fatigue after training. However, the present results are
similar to a previous study that also reported that maximal blood lactate
concentrations did not change significantly during a time trial (approximately
60 minutes) after intensified training designed to induce OTS [4]. Future
research should therefore examine additional mechanisms that may be associated
with the earlier attainment of fatigue following overtraining.
References
[1]. Edge, J. et al. (2002). 7th Annual Congress of the ECSS, Athens,
Greece: 622.
[2]. Fry, R. et al. (1991). Sports Medicine, 12 (1), 32-65.
[3]. Fry, R. et al. (1994). British Journal of Sports Medicine, 28(4),
241-246.
[4[. Halsom, S. et al. (2002). Journal of Applied Physiology, 93, 947-956.

http://www.icsspe.org/portal/bulletin-january2005.htm
Possible Mechanisms underlying the decrease in
performance associated with Overtraining Syndrome (OTS)
David Bishop, Australia
|