Download Slide 1 1 - Force and Motion Foundation

Effects of Volitional Preemptive Abdominal
Contraction on Trunk and Lower Extremity
Biomechanics and Neuromuscular Control
During a Drop Vertical Jump
R. Haddas, T. Hooper, P. Sizer, R. James
Center for Rehabilitation Research, TTUHSC, Lubbock, Texas
Methods
A repeated measures design was used to examine the
effects of VPAC using an abdominal bracing maneuver5 on
biomechanical and neuromuscular control variables
measured during a DVJ from two heights. Thirty-two
healthy and active subjects (17 men and 15 women;
M±SD age 24.6±2.4 years, height 1.76±0.12 m, and mass
77.6±19.0 kg) participated after providing informed
consent. Volunteers were excluded if they reported LE
pain, history of LE or lumbar spine surgery, active
abdominal or gastrointestinal condition, or present
pregnancy. Subjects were taught and allowed to practice
VPAC. The presence of VPAC during the DVJ was verified
by a review of the recorded electromyographic (EMG) data
immediately after each trial. Eighteen reflective markers
were placed on the LE and trunk. Surface EMG electrodes
were placed over eight muscles on the right side LE and
trunk. Each subject performed three successful DVJs from
a raised platform at two heights (30 and 50 cm) with and
without VPAC, presented in a random order. 3D kinematic
data were recorded using an 8 camera Vicon-Peak system
(120 Hz), while ground reaction force (GRF; Bertec Corp.)
and EMG (Noraxon, Inc.) were recorded simultaneously
(1200 Hz). Data were pre-processed using Motus (ViconPeak), exported and reduced using custom laboratory
algorithms developed in Matlab (Mathworks). Dependent
variables included trunk, hip, knee and ankle joint angles,
and internal joint moments in 3D, sagittal plane LE joint
powers, EMG root mean square (RMS) amplitudes preand post-initial ground contact. Descriptive statistics for 96
biomechanical and neuromuscular control variables were
incorporated in an exploratory analysis: kinematic maxima,
minima, range of motion and values at initial contact,
kinetic maxima, minima and impulse, and the pre- and
post-contact EMG RMS values were statistically analyzed
(SPSS; α=0.05).
No VPAC
Lower Extremity 30 cm Drop Vertical Jump
VPAC
% Change
30.0
Knee Internal
Rotation (deg)
25.6
25.0
Knee Flexion
(deg)
20.0
Change (%)
Anterior cruciate ligament (ACL) injuries continue to pose
a significant concern relative to short- and long-term
effects on quality of life and participation in physical
activity1. Recognizing an increased risk for ACL injury and
discovering interventions that may reduce that risk are
important to patients, clinicians, and researchers. Altered
neuromuscular control plays a prominent role in most ACL
injury models. Previous research has focused primarily on
examining the neuromuscular control of the lower
extremity (LE)2. However, LE control also be additionally
influenced by abdominal muscle activation3. Individuals
can actively modify pelvic control parameters through
volitional muscle recruitment during dynamic movements
using volitional preemptive abdominal contractions
(VPAC)4-5 (Figure 1). The effects of abdominal muscle
contraction may be transmitted to the LE via the pelvis,
which provides a mechanical link between the trunk and
the LE, thus influencing the entire lower quarter
mechanical chain6. Although, VPAC has been shown to
improve spine stability7, very little is known about the
effects of VPAC on trunk and LE biomechanics and
neuromuscular control in healthy individuals, with
implications for ACL injury risk. The purpose of our study
was to determine the effects of VPAC on trunk and LE
biomechanics and neuromuscular control during a drop
vertical jump (DVJ) landing sequence. We hypothesized
that VPAC, would improve trunk and LE stabilization and
neuromuscular control during the landing phase of the
DVJ.
Figure 2.
14.3
15.0
10.0
9.8
8.7
5.0
Abdominal bracing emphasizes a global contraction of
all the abdominal muscles and lumbar extensors, where
no movement should occur in the abdominal wall during
the activation8.
Results
0.0
Statistically significant p < 0.05
Figure 3.
Lower Extremity 50 cm Drop Vertical Jump
% Change
40.0
30.0
At the 50 cm landing height, VPAC resulted in
statistically significant (P≤0.05) decreases in: (1) ankle
inversion angle; (2) hip energy absorption (Figure 3);
and (3) external oblique muscle activity post-contact.
These decreases were accompanied by significant
increases in: (1) knee flexion angle at contact; (2)
medial hamstring activity pre-contact; (3) hip flexion
angle at contact; (4) trunk left rotation angle postcontact; (5) trunk left rotation angle at contact; and (6)
greater external oblique muscle activity pre-contact
(Table 2).
Table 1.
Statistically Significant Variables for 30 cm Drop Vertical Jump
No VPAC VPAC
Mean ± SD Effect Size P Value Power
Variable
Mean ± SD
Knee Flexion
Total ROM (deg)
Knee Maximum Internal
Rotation Angle (deg)
Knee Internal Rotation
Total ROM (deg)
Knee Abduction
Moment (Nm)
Knee Energy Absorption (W)
40.9±12.5
44.9±13.7
0.14
0.037
0.56
26.2±18.5
29.2±19.4
0.13
0.046
0.52
31.0±10.9
33.7±13.6
0.13
0.050
0.51
15.0±6.6
15.4±6.4
0.46
0.043
0.56
29.7±64.1
37.3±69.0
0.13
0.046
0.52
Medial Hamstring
Post -Contact (µV)
Trunk Left Rotation (deg)
0.343±0.2
0.392±0.2
0.17
0.019
0.67
0. 28±0.2
0.34±0. 1
0.21
0.009
0.77
External Oblique
Pre-Contact (µV)
External Oblique
Post-Contact (µV)
0.165±0.1
0.201±0.1
0.17
0.020
0.66
0.169±0.1
0.199±0.1
0.19
0.013
0.72
(Partial η2)
Table 2.
Statistically Significant Variables for 50 cm Drop Vertical Jump
No VPAC VPAC
Mean ± SD Effect Size P Value Power
15.8
7.1
10.0
Medial Hamstring
Pre-Contact (µV)
0.0
-10.0
-8.0
-20.0
-30.3
-40.0
Hip Flexion at
Contact (deg)
Hip Energy
Absorption (W)
Statistically significant p < 0.05
Conclusion
The use of VPAC altered LE and trunk biomechanics and
neuromuscular control when performing DVJ from 30 and
50 cm heights, although not all changes were consistent
with greater knee protection. More potential clinical
advantages were observed at the lower height, where
increased medial hamstring activity, knee flexion and knee
energy absorption during VPAC suggest an enhanced
protective LE response. Similarly, VPAC triggered
increased external oblique activity that may indicate
enhanced trunk stability under lower loading conditions,
when more neuromuscular control options are available.
The demands of the 50 cm DVJ may have superseded the
effectiveness
of
VPAC.
Similarly,
competing
neuromuscular control requirements (trunk vs. LE) may
have resulted in less attention to the abdominal
contraction, and greater attention to the task at the higher
height. The use of VPAC increases abdominal muscle
activity, stabilizing the trunk against novel perturbations9
and increased medial hamstring activity protects ACL2. In
the current VPAC study, VPAC demonstrates potential
clinical advantages when landing from a commonly used
height. In addition, these results suggest an enhanced
protective knee response and improved trunk stability with
VPAC use. Further study is needed to determine whether
VPAC is effective for reducing ACL injury risk. The effects
of VPAC on pelvis motion and relative motion among
spinal segments should be examined as well.
(Partial η2)
Ankle Inversion (deg)
14.2±8.1
9.9±8.9
0.42
0.037
0.51
Knee Flexion
at Contact (deg)
Medial Hamstring
Pre-Contact (µV)
Hip Flexion
at Contact (deg)
Hip Energy Absorption (W)
16.5±8.0
19.1±7.9
0.24
0.005
0.84
0.164±0.1
0.219±0.163
0.21
0.010
0.76
25.4±7.2
27.2±6.8
0.18
0.017
0.68
301.6±254.3
277.6±253.6
0.21
0.045
0.54
1.25±0.1
1.29±0.1
0.17
0.020
0.66
1.26±0.1
1.29±0.1
0.16
0.026
0.62
0.197±0.1
0.231±0.1
0.17
0.020
0.67
Trunk Left Rotation
at Contact (deg)
Trunk Left Rotation
Post-Contact (deg)
External Oblique
Knee Flexion at
Contact (deg)
20.0
-30.0
Mean ± SD
Ankle Inversion
(deg)
33.5
At the 30 cm landing height, VPAC resulted in
statistically significant (P ≤ 0.05) increases in: (1) knee
internal rotation angle; (2) knee flexion range of motion;
(3) knee internal abduction moment; (4) knee energy
absorption; (5) medial hamstring post contact activity
(Figure 2); (6) trunk left rotation; and (7) external oblique
activity pre- and post-contact (Table 1).
Variable
Knee Internal
Abduction
Moment (Nm)
Knee Energy
Absorption (W)
Medial Hamstring
Post-Contact (µV)
2.7
Change (%)
Introduction
Figure 1.
References
1. Arendt E, et al. Am J Sports Med 23, 694‐701, 1995.
2. Hewett TE, et al. Instr Course Lect 56, 397‐406, 2007.
3. Hodges PW, et el. Ergonomics 40, 1220‐1230, 1997.
4. Oh et al. J Orthop Sports Phys Ther 37, 320-324 2007.
5. Park KN, et al. Arch Phys Med Rehabil 92,1477-1483, 2011.
6. Duval K, et al. Gait Posture 32, 637-640, 2010.