Fatigue could reduce skills and cause injuries and muscle weakness
during sport because the brain does not consider the extra effort
required for movement, Monash University researchers have found.
Professor Uwe Proske, from Monash’s Department of Physiology, found
when muscles were weakened from overuse or fatigue, limb control was
affected, particularly if the person couldn’t see their limbs.
The study, which has been published in the Journal of
Physiology, showed muscles needed to work harder to compensate for
fatigue, which led to uncertainty about where the limb was.
"In the absence of sight, people judge the position of their
limbs based on the amount of effort required to lift them against the
force of gravity," Professor Proske said. "Take gravity away, as
happens to astronauts, and they have real trouble carrying out skilled
"In our experiments we found that when the muscles in one arm
were fatigued, the effort required to maintain a set arm position was
much greater. When asked to keep both arms in a similar position, where
one arm was fatigued and the other was not, the arms did not align.
"That was unexpected. Previously it was believed that fatigue had nothing to do with the body’s sense of position," he said.
Professor Proske said the findings could have implications for
sports that required skilled actions such as serving a tennis ball,
throwing a javelin or shooting a bow and arrow.
He said it could also result in loss of control over stride
length during running – leading to stretched hamstrings and other
"When a tennis player is serving, they don’t watch where their
shoulders are, they rely on the brain’s knowledge of how much effort is
required to maintain the best position, to get the ball where it needs
"However, if the limbs are fatigued the brain must activate
them harder and this leads to errors about where the different body
parts are located."
Professor Proske said the research could also offer insight
into the symptoms of some motor system diseases such as Parkinson’s
disease. The abnormal movements were likely to relate, in part, to a
disturbed sense of effort, he said.
Research Australia. June 2005.