Significant difference was found in the performance of SLH between the pre-activation quadriceps/hamstring (Q/H) EMG ratio. The ratio increased from pre (0.98) to post (1.02) testing for both interventions.

1
Female athletes who participate in jumping and
cutting sports are 4-6 times more likely to
sustain serious knee injuries than male athletes
participating in the same sport. These injuries
are linked to improper landing techniques and
ineffective neuromuscular activation patterns.
The purposes of this study were to evaluate the
effects of instruction of correct landing
technique on the impact impulse, the
pre-activation and co-activation electromyography
ratios of quadriceps and hamstring muscles, and
to asses the differences between two methods of
instruction. We expected the pre-activation and
co-activation of hamstrings to increase, with the
ratio (Q/H) remaining constant or decreasing and
Impact impulse to decrease. Six healthy female
subjects participated in this study. Each subject
was assessed on the performance of single leg hop
(SLH), relaxed single leg hop (RSLH), and drop
jumps (DJ). One group watched video on three
separate occasions for 20 minutes each and one
group was personally trained on two separate
occasions for 30 minutes each. Impact impulse and
EMG data were collected before and after
training. A 2 X 2 repeated measures ANOVA
(plt0.05) was used to identify differences between
pre and post intervention. There were no
differences in all analyzed variables, except for
the pre-activation quadriceps/hamstring (Q/H) EMG
ratio which increased significantly for the SLH
from pre (0.98) to post (1.02) testing for both
interventions.

• Significant difference was found in the
  performance of SLH between the pre-activation
  quadriceps/hamstring (Q/H) EMG ratio. The ratio
  increased from pre (0.98) to post (1.02) testing
  for both interventions.
• Q/H Pre-activation EMG Ratio
• There was no significant difference found in the
  co-activation EMG and Impact impulse, between the
  pre- and post-tests of SLH.
• There were no significant differences found in
  the pre-activation and co-activation EMG ratios
  and Impact impulse during the performance of RLH
  and DJs between the pre- and post-tests.
• When the two methods of Intervention (watching a
  video and personal training) were compared, no
  differences were found in the pre- and post
  measurements.

STUDY DESIGN A 2 x 2 (Intervention x Time)
repeated measures design. Independent variables
Intervention (Instruction through video, watching
an expert perform the correct technique of
jump-landing and Instruction through personal
training on the correct method of jump-landing)
and Time (Pre, Post). Dependent variables Impact
impulse and pre-activation and co-activation
Electromyography ratios of hamstring and
quadriceps muscles (Figure 1). Alpha level was
set at 0.05. Surface Electromyographic
Measurements A bipolar surface electrode
arrangement was placed along the longitudinal
axis of the vastus lateralis, medialis and
hamstring muscles. Local areas of the skin were
cleaned with alcohol and lightly rubbed with
emery paper. The EMG signals were recorded in
microvolts. Impact Impulse Landing forces were
sampled at 1000 Hz, using an AMTI Force plate.
Impact impulse was computed by integrating the
vertical force from ground contact to 100 ms
after contact (Figures 2 3).
Figure 3. EMG and vertical force.
Pre-testing was done on Day 1. Impact
impulse was measured using Force plate. EMG of
Vastus lateralis, vastus medialis and Hamstrings
muscles was recorded. Each subject was assessed
on the performance of single leg hop (SLH),
relaxed single leg hop (RSLH), and drop jumps
(DJ), see Figure 2. The three best trials of each
jump were recorded. The subjects were then
randomly divided into two groups. One group
watched video on three separate occasions for 20
minutes each and the other group was personally
trained on two separate occasions for 30 minutes
each. Post-testing was done on Day 5. Impact
impulse and EMG data were collected during
post-testing.
Figure 2. Drop jump onto force plate.
Muscular preactivation was measured 100 ms prior
to ground contact.
The purposes of this study were to evaluate the
effects of instruction of correct landing
technique on the impact impulse, the
pre-activation and co-activation electromyography
ratios of quadriceps and hamstring muscles, and
to assess the differences between two methods of
instruction.

• Based on the EMG results of this study, the
  pre-activation and co-activation excitation of
  hamstrings can be increased, with training,.
• Based on the 2-3 training sessions performed, one
  type of the training program was not better than
  the other.
• SUGGESTIONS FOR FUTURE RESEARCH
• As the post-testing was done on the day
  immediately after the training, our subjects
  experienced fatigue in the muscles of the lower
  limb. For the ratio (Q/H) to remain constant or
  decrease, onset of fatigue in the Hamstrings
  should be avoided. A period of rest between the
  training and post-testing might favorably
  increase the pre- and co-activation of hamstrings
  and decrease the impact impulse.
• An increase in the number of training sessions
  for both the methods of Intervention is suggested
  to bring out significant differences.

A 2 x 2 (Intervention x Time) repeated measures
ANOVA was done to compare the dependent
variables. Alpha was set at 0.05. Tukey
Post-hoc testing was performed.
Figure 1 Pallavi Bellamkonda Placing EMG
Electrodes in ESRL in University of Texas at
Arlington.