1. Abstract:
Introduction. Normally people perform a partial squat during the
countermovement phase of a vertical jump. As leg strength
increases vertical jump performance can increase (Alexander,
1995). One way to increase leg strength is to perform a back squat.
Purpose. Due to training specificity the purpose of this study was
to investigate the impact of squat depth through resistance training
on vertical jump performance. Method. Sixteen subjects were
randomly assigned to either a half-squat (HS) or full-squat (FS)
group. During the six-week training period, FS subjects performed a
squat exercise to 90-degrees of knee flexion, while HS subjects
performed a squat exercise to 135-degrees of knee flexion. Results.
No significant difference was found between the two groups
(n=.915). Conclusion. Based on this study, squat depth training
does not show any significant differences on vertical jump
performance.
Introduction.
Many sports use various training techniques to enhance an
athlete’s power output. The longer a muscle is acting against a
resistance, as in a deeper squat, the more time there is going to be
available for the generation of muscular force. An increase in the
period over which a muscle generates force can lead to a
generation of greater force, and therefore greater vertical jump
height (Domire, 2007). An investigation of optimal knee angle on
vertical jump performance showed the best performances
approximately 90 and 115 degrees of knee flexion (Martin, 1969).
The degrees of knee flexion performed on a FS and HS are similar to
the degrees of knee flexion performed during a vertical jump. Since
the window of optimal knee flexion between the two exercises are
closely related, we hypothesize that resistance exercise done using
the HS and FS protocols will show no significant differences in
vertical jump performance.
Method
Sixteen college-aged students of mixed gender and athletic ability
were recruited for this study. Subjects completed a vertical jump
pre-test using the National Strength and Conditioning Association
(NSCA) standards. After testing, subjects were randomly assigned
to either a full-squat (FS) or half-squat (HS) group. The FS group
performed a squat lift to 90-degrees of knee flexion while the HS
group performed 135-degrees of knee flexion, as measured with a
goniometer placed at the knee joint. Subjects were tested to a 1-
repetition maximum (1-RM) in order to prescribe a workout
protocol where both groups performed their squat exercises at 80%
1-RM. Training followed a six week program that included an
identical full body workout differing only in the squat exercise. At
the end of six weeks subjects were given a week of rest, after which
they completed a vertical jump post-test. Measurements were
compared using an independent T-test.
Results
Of the sixteen subjects who were initially recruited and cleared for
participation, fourteen successfully completed the study. One subject
voluntarily withdrew and the other was unable to complete the study
due to injury. Data was collected from the following groups: HS (n=6)
and FS (n=8). Overall there was an increase in vertical jump
performance in both groups. The HS group showed a mean
improvement of 0.83 inches with a standard deviation of 1.03 inches
and the FS group showed a mean improvement of 1.00 inches with a
standard deviation of 1.25 inches.
Independent T-test Results:
The mean difference between the vertical jump improvement of the
two groups showed no significant difference (p=.915).
Discussion
There was no significant difference in the performance of the vertical
jump when comparing the two groups. Subjects performed a resistance
training program that most likely increased muscle strength and power
output, allowing for a greater vertical jumping ability. However, other
factors such as activity level, diet, and weight loss could have affected
their performance. Ankle flexion was also not accounted for in the
determination of the knee angles, therefore subjects did not perform a
squat with their thighs parallel to the floor. Regardless of outside
factors the data suggest that there may be a number of squat
protocols, combined with a full-body workout, that could be
implemented in training to improve one’s vertical jump. Further
research could be done on optimal jump knee angle when a
countermovement phase is involved as well as squat exercises in which
the subjects would reach parallel with their thighs. Researchers should
look at different percentages of 1-RM that would be prescribed to
allow for more explosive movements during the squat exercise.
Although this study showed no significant difference between the two
groups, it has opened a door for further research regarding the effects
of different squat techniques and protocols on vertical jump
performance.
References
Domire, Z., & Challis, J. (2007). The influence of squat depth on maximal vertical
jump performance. Journal of Sports Sciences, 25(2), 193-200.
Martin, T. P., & Stull, G. A. (1969). Effects of various knee angle and foot spacing
combinations on performance in the vertical jump Res Quart AAHPER.
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21.5
Pre Test
(HS)
Post Test
(HS)
Pre Test
(FS)
Post Test
(FS)
Inches
Difference of Pre and Post Vertical Jump Test