Download Effects of Volitional Preemptive Abdominal Contraction on Trunk and

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
Introduction
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.
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 (Vicon-Peak), 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 pre- and 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).
Results
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). 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 post-contact; (5) trunk left rotation angle at
contact; and (6) greater external oblique muscle activity pre-contact (Table 2).
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.
Reference
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.
7. Stanton T, et al. Spine 33, 694-701, 2008.
8. McGill S, Low Back Disorders, 2007.
9. Grenier SG, et al. Arch Phys Med Rehabil 88, 54-62, 2007.
Table 1. Statistically Significant Variables for 30 cm Drop Vertical Jump
No VPAC
VPAC
Variable
Mean ± SD
Mean ± SD
Effect Size
(Partial η2)
P Value
Power
Knee Flexion
Total ROM (deg)
40.9±12.5
44.9±13.7
0.14
0.037
0.56
Knee Maximum Internal
Rotation Angle (deg)
26.2±18.5
29.2±19.4
0.13
0.046
0.52
Knee Internal Rotation
Total ROM (deg)
31.0±10.9
33.7±13.6
0.13
0.050
0.51
Knee Abduction
Moment (Nm)
15.0±6.6
15.4±6.4
0.46
0.043
0.56
Knee Energy Absorption (W)
29.7±64.1
37.3±69.0
0.13
0.046
0.52
Medial Hamstring Post -Contact (µV)
0.343±0.2
0.392±0.2
0.17
0.019
0.67
Trunk Left Rotation (deg)
0. 28±0.2
0.34±0. 1
0.21
0.009
0.77
External Oblique
Pre-Contact (µV)
0.165±0.1
0.201±0.1
0.17
0.020
0.66
External Oblique
Post-Contact (µV)
0.169±0.1
0.199±0.1
0.19
0.013
0.72
Table 2. Statistically Significant Variables for 50 cm Drop Vertical Jump
Variable
No VPAC
VPAC
Mean ± SD
Mean ± SD
Effect Size
P Value Power
(Partial η2)
Ankle Inversion (deg)
14.2±8.1
9.9±8.9
0.42
0.037
0.51
Knee Flexion
16.5±8.0
19.1±7.9
0.24
0.005
0.84
Medial Hamstring Pre-Contact (µV)
0.164±0.1
0.219±0.163 0.21
0.010
0.76
Hip Flexion at Contact (deg)
25.4±7.2
27.2±6.8
0.18
0.017
0.68
Hip Energy Absorption (W)
301.6±254.3 277.6±253.6 0.21
0.045
0.54
Trunk Left Rotation at Contact (deg)
1.25±0.1
1.29±0.1
0.17
0.020
0.66
Trunk Left Rotation Post-Contact (deg) 1.26±0.1
1.29±0.1
0.16
0.026
0.62
External Oblique Pre-Contact (µV)
0.197±0.1
0.231±0.1
0.17
0.020
0.67
External Oblique Post-Contact (µV)
0.209±0.1
0.177±0.1
0.16
0.025
0.63
at Contact (deg)
Figure 1.
Figure 2. Lower Extremity 30 cm Drop Vertical Jump (%
Change)
Figure 3. Lower Extremity 50 cm Drop Vertical Jump (%
Change)