1. The effect of anterior cruciate ligament injury on the
magnitude of activation of the quadriceps and hamstrings
K P Tyson, S L Keays, J E Bullock-Saxton, P A Newcombe
The ACL provides 86% of the primary passive constraint against anterior
tibial translation [Butler et al., 1980] and is a rotary stabiliser – main
deficit is knee instability.
However, rupture results in secondary changes in muscle activation
[Snyder-Mackler et al., 1994], strength [Keays et al., 2003], size [Tsepsis
et al., 2006] and fatigability [Bosker et al., Unpublished]
And sensorimotor changes, for example, loss of proprioception [Muller,
1983; Palmer, 1958; Tsuda et al., 2001] and loss the gamma-muscle-
spindle system function [Barratta et al., 1988; Fonseca et al., 2004;
Johansson et al., 1986
To date, differences in magnitude of muscle activation during dynamic
simulated sporting tasks have not been studied

2. Method
We aimed to assess the magnitude of activation of VMO, VL and BF during 2 sport-type activities – namely
kicking and hopping. We studied 15 ACLD (8 males 7 females; mean age 29.33 ± 7.81years) and 7 healthy (7
males 0 females; mean age 27.77 ± 6.81years) subjects using Electromyography.

3. Data
Data converted to RMS score using an epoch of 100ms by blind assessor
RMS =

4. Results
Measure Muscle Injured vs. Uninjured
Injured
Mean (SD)
Uninjured
Mean (SD)
P Value
Injured vs. Controls
Injured
Mean (SD)
Controls
Mean (SD)
P Value
Take-off activity VMO
VL
BF
1.4890 (.84199)
1.0483 (.46142)
.9511 (.42981)
1.5916 (.90113)
1.1730 (.64521)
.6280 (.19547)
P = 0.699
P = 0.501
P = 0.009**
1.4890 (.84199)
1.0483 (.46142)
.9511 (.42981)
1.0638 (.39346)
.8228 (.38609)
.4823 (.12519)
P = 0.229
P = 0.286
P = 0.012*
Landing Activity VMO
VL
BF
1.3400 (1.00614)
.9517 (.45011)
.8859 (.36747)
1.2825 (.97115)
.9604 (.74235)
.6983 (.34691)
P = 0.852
P = 0.963
P = 0.059 (trend)
1.3400 (1.00614)
.9517 (.45011)
.8859 (.36747)
.7703 (.29121)
.6550 (.33439)
.4961 (.14993)
P = 0.088 (trend)
P = 0.145
P = 0.016*
Kicking Activity VMO
VL
BF
.2578 (.21326)
.2350 (.17567)
.4517 (.16754)
.1695 (.12206)
.3117 (.16259)
.2651 (.13727)
P = 0.241
P = 0.482
P = 0.033*
.4012 (.54672)
.3527 (.10334)
.6955 (.48876)
.2136 (.15354)
.2548 (.12303)
.3584 (.12106)
P = 0.425
P = 0.078 (trend)
P = 0.023*
Co-contraction VMO
VL
BF
1.5707 (1.62868)
.8449 (.50016)
.4790 (.24542)
1.1623 (.89937)
.8396 (.59094)
.2550 (.24967)
P = 0.410
P = 0.976
P = 0.033*
1.5707 (1.62868)
.8449 (.50016)
.4790 (.24542)
.7674 (.23263)
.6904 (.28326)
.2098 (.09862)
P = 0.467
P = 0.217
P = 0.014*

5. Conclusion
Our findings were not unexpected – hamstrings are said to act as agonists to the ACL.
Over many years physiotherapists have been taught to emphasise hamstring co-contraction
because of the role the hamstrings play in posterior tibial translation, this study shows more
emphasis should be placed on the quadriceps without neglecting the hamstrings
There are several theories that show that overemphasis of the hamstrings results in changes
in decreased selective activation of muscles and increased compressive forces. Possibly
predisposing to the development of osteoarthritis.
However this study has brought home a strong message that physiotherapists need to re-
focus on the quadriceps, especially VMO