AGONIST VERSUS ANTAGONIST MUSCLE FATIGUE

1
AGONIST VERSUS ANTAGONIST MUSCLE FATIGUE EFFECTS
ON MUSCLE ACTIVATION PATTERNS DUR- ING LANDING
Kellis Eleftherios, Kouvelioti Vasiliki
(Aristotle University of Thessaloniki, Greece)
The neuromuscular system needs to adjust its
level of ac-tivation and proceed with necessary
segmental and joint movements in order to reduce
joint forces and maintain joint stability. Taken
into account the potentially different roles of
agonist and antagonist muscle action while
per-forming a movement, it can be assumed that
selective fa-tigue of either of them would cause
different changes in the neural activation and
temporal patterns of the move-ment. Evidence
suggests that agonist fatigue affects move-ment
kinematics more than antagonist muscle fatigue
1. A better understanding of the above effects
may lead to the use of injury prevention
strategies that decrease the loads during
landing. Therefore the objective of this study
was to investigate the effects of knee extension
and flex-ion fatigue, on vertical ground reaction
force (GRF) and electromyographic (EMG)
characteristics during landing. Twenty healthy
subjects (age 23.91.37 yrs, height 174.8 10.3
cm, mass 68.9512.09 kg), performed 2 sets of
repeated maximal concentric efforts of the knee
extensors and flexors at 120o/sec, until they
could no longer consis-tently produce 50 of
maximum torque. All subjects were asked to
perform three single leg landings from a 30cm
drop height on a force plate, before and after
each fatigue protocol. Surface EMG of vastus
medialis (VM), vastus lat-eralis (VL), biceps
femoris (BF) and gastrocnemius (GAS) and vertical
GRFs were recorded. Vertical GRFs declined
significantly (plt 0.05) after knee extension
fatigue but not after knee flexion fatigue. Knee
extension fatigue caused a decline in EMG
pre-activation of the BF and increases in vastii
muscle EMGs (p lt 0.05). In contrast, knee
flex-ion fatigue caused a decline in GAS EMG and
inconsis-tent alterations in VM and VL EMGs (p lt
0.05). These results indicate that muscle
activation responses during landing to fatigue
depend on the type of muscle being fa-tigued.
Knee extension fatigue caused subjects to use an
antagonist inhibition strategy by minimizing
antagonist co-activation around the knee and rely
more on quadriceps activity. In contrast,
fatiguing the antagonist muscles had less effect
on landing performance and mainly caused
al-terations in gastrocnemius EMG which suggests
that sub-jects might have altered the
contribution of ankle muscula-ture to absorb
impact forces upon landing. These changes in
muscle activation and coactivation ratios because
of fa-tigue are suggested to alter knee joint
stability and increase anterior cruciate ligament
injury risk. Reference 1 Jaric S, Blesic S,
Milanovic S et al.(2000) Eur J Appl Phys 80
379-385. Keywords Electromyography, Movement
Control, Fatigue 12thAnnual Congress of the
ECSS, 1114 July 2007, Jyväskylä, Finland I