Preferential quadriceps activation in female athletes with incremental increases in landing intensity.

TLDR: Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity, which may contribute to the increased risk of ACL injury in female athletes.

Abstract: The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes.

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Preferential Quadriceps Activation in Female Athletes With
Incremental Increases in Landing Intensity
Kevin R. Ford,
Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children’s
Hospital Medical Center, and with the Department of Pediatrics, College of Medicine, University
of Cincinnati, Cincinnati, OH
Gregory D. Myer,
Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children’s
Hospital Medical Center, Cincinnati, OH; the Departments of Pediatrics and Orthopaedic Surgery,
College of Medicine, University of Cincinnati, Cincinnati, OH; Athletic Training Division, School of
Allied Medical Professions, Ohio State University, Columbus, OH; and with the Departments of
Athletic Training, Sports Orthopaedics, and Pediatric Science Rocky Mountain University of
Health Professions, Provo, UT
Laura C. Schmitt,
Division of Physical Therapy, School of Allied Medical Professions, Ohio State University,
Columbus, OH; and the Sports Medicine Biodynamics Center and Human Performance
Laboratory and the Division of Occupational Therapy and Physical Therapy, Cincinnati Children’s
Hospital Medical Center, Cincinnati, OH
Timothy L. Uhl, and
Department of Rehabilitation Sciences and the Department of Kinesiology and Health Promotion,
University of Kentucky, Lexington, KY
Timothy E. Hewett
Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati Children’s
Hospital Medical Center; the Department of Pediatrics, College of Medicine, University of
Cincinnati; and the Departments of Orthopaedic Surgery and Biomedical Engineering, University
of Cincinnati, Cincinnati, OH, and the Ohio State University Sports Medicine Sports Health and
Performance Institute, Departments of Physiology and Cell Biology, and Orthopaedic Surgery,
Columbus, OH; and the School of Allied Medical Professions and the College of Medicine, Family
Medicine and Biomedical Engineering, Ohio State University, Columbus, OH
Abstract
The purpose of this study was to identify alterations in preparatory muscle activation patterns
across different drop heights in female athletes. Sixteen female high school volleyball players
performed the drop vertical jump from three different drop heights. Surface electromyography of
the quadriceps and hamstrings were collected during the movement trials. As the drop height
increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05).
However, the hamstrings activation showed no similar increases relative to drop height. Female
athletes appear to preferentially rely on increased quadriceps activation, without an increase in
hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio
NIH Public Access
Author Manuscript
J Appl Biomech. Author manuscript; available in PMC 2014 November 06.
Published in final edited form as:
J Appl Biomech. 2011 August ; 27(3): 215–222.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript

of the hamstrings relative to quadriceps before landing may represent altered dynamic knee
stability and may contribute to the increased risk of ACL injury in female athletes.
Keywords
electromyography; drop vertical jump; anterior cruciate ligament; knee injury; co-contraction
Female athletes suffer anterior cruciate ligament (ACL) injuries at a greater rate than males
participating in the same landing and pivoting sports (Arendt & Dick, 1995; Malone et al.,
1993). Decreased dynamic neuromuscular control of the knee or active restraint likely
contributes to increased risk of ACL injury in female athletes (Hewett et al., 2005).
Decreased neuromuscular control of the joint may increase the stress on passive ligamentous
structures, including the ACL, in a manner that may ultimately exceed the failure strength of
the ligament (Li et al., 1999; Markolf et al., 1978).
Increased hamstrings force has been shown, in vitro, to greatly decrease relative strain on
the ACL during the exion phase of simulated jump landings (Withrow et al., 2008).
Increased strength and recruitment of the hamstrings musculature may also decrease
excessive frontal plane rotations (Lloyd & Buchanan, 2001). Female athletes demonstrate
increased frontal plane motion and moments during a variety of athletic maneuvers
compared with males (Ford et al., 2003, 2005, 2006; Hewett et al., 2006; Kernozek et al.,
2005; McLean et al., 2004). Decreased ability to control external frontal plane loads in
female athletes may be the symptom of decreased co-contraction of the hamstrings and
quadriceps musculature in female athletes (Hewett et al., 2008). Accordingly, increased
quadriceps activation with decreased relative hamstrings activation may contribute to the
increased risk of ACL injury in female athletes (Hewett et al., 2005; Myer et al., 2008).
The current study aims to determine the relationship between hamstrings and quadriceps
activation during plyometric activities with increasing drop heights in female athletes.
Specifically, the purpose was to identify alterations in muscle activation strategies across
three different drop heights of a drop vertical jump. The primary hypothesis was that muscle
activation would be greater at higher drop heights during the preparatory phase of landing in
the quadriceps, but not the hamstrings, musculature. Secondly, we hypothesized that muscle
activation would be greater at greater drop heights during the reactive phase of landing in
the quadriceps but not the hamstrings. An increase in quadriceps activation, in the absence
of increased hamstrings activation may be indicative of a preferential extensor activation
pattern in females during increased intensity of plyometric activity.
Methods
Subjects
Sixteen female high school volleyball players volunteered to participate in this study (height
169 ± 5 cm, mass 61.7 ± 5.4 kg). Informed written consent, approved by Cincinnati
Children’s Hospital institutional review board, was obtained from the parent or parental
guardian of each subject. Child assent was also obtained from each subject before
participation.
Ford et al.
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J Appl Biomech. Author manuscript; available in PMC 2014 November 06.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript

Instrumentation
A telemetry surface electromyography system (TeleMyo 2400, Noraxon) was used to record
muscle activity on the right lower extremity. A custom backpack was worn by each subject
during data collection to secure the electromyography transmitter. The unit specifications
included an amplifier gain of 2000, hardware bandpass filter of 10–500 Hz, an input
impedance of >1MΩ and a common-mode rejection ratio of >100 dB.
A 10-camera motion analysis system (Eagle cameras, Motion Analysis Corporation, Santa
Rosa, CA) was used to capture three-dimensional marker trajectories of the right lower
extremity. Ground reaction force was captured with one force platform (AMTI, Watertown,
MA) embedded in the laboratory floor. The trials were collected in EVaRT (Version 5,
Motion Analysis Corporation, Santa Rosa, CA) with synchronized video (240 Hz) and
analog data (force and electromyography; 1200 Hz).
Procedures
The testing was completed during a single session. The subject’s skin was prepared by
shaving hair that was present and vigorously cleansing the location with an alcohol swab.
Disposable, self-adhesive Ag/AgCl dual electrodes with sensor diameter of 1 cm and
interelectrode distance of 2 cm (Noraxon #272, Scottsdale, AZ) were applied to five muscles
on the right lower extremity: hamstrings (semitendinosus, biceps femoris) and quadriceps
(rectus femoris, vastus medialis, and vastus lateralis). Electrode placement was determined
using protocols described previously in the literature (Boling et al., 2006; Cram et al., 1998)
and confirmed by visually inspecting waveforms on an oscilloscope (MyoResearch,
Noraxon) using standard manual muscle testing protocols. Wires were secured with elastic
tape to reduce movement artifact during testing.
Maximum activation was recorded from each muscle during a maximum voluntary isometric
contraction. Subjects were seated on a dynamometer (Biodex Medical Systems, Shirley,
NY) with the trunk perpendicular to floor, the hip flexed to 90°, and the knee flexed to 60°
(Brindle et al., 2002). Practice trials were performed on the dynamometer with both visual
and verbal cues on their technical performance. Each subject performed three maximum
effort isometric contractions of the quadriceps and hamstrings muscle groups. Each
isometric contraction lasted 5 s with a 30-s rest between each trial. For the dynamic trials,
three trials of a drop vertical jump were performed at three randomly presented drop heights
(15 cm, 30 cm, and 45 cm). Participants were instructed to drop directly down off the box
with both feet leaving the box at the same time and as soon as they touched the ground to
immediately perform a maximum vertical jump. The first landing on the force platform (i.e.,
the drop from the box) was used for analysis.
Thirty-seven reflective markers were placed on the subject, as previously described (Ford et
al., 2007), with a minimum of three markers per lower extremity segment. A static trial was
collected in which the subject was instructed to stand still in the anatomical position with
foot placement standardized. This static measurement was used as each subject’s neutral
(zero) alignment.
Ford et al.
Page 3
J Appl Biomech. Author manuscript; available in PMC 2014 November 06.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript

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The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. The resultant decreased activation ratio NIH Public Access Author Manuscript J Appl Biomech.