Hamstring Strains Project- FINAL!

1INCIDENCE OF HAMSTRING STRAINS IN SPRINTERS
Incidence of Hamstring Strains in Sprinters
HP565: Applied Kinesiology and Biomechanics
Candice Shadgoo, Felicia Sciortino, Djenne Parris, Stacey Sousa
Professor Kenneth Holt
Spring 2016
Photograph of
Felicia Sciortino,
taken by: Djenne
Parris (2015)

Table of Contents
Introduction ………………………………………………………………………………………….. 3
Methods ……………………………………………………………………………………………… 5
Results ……………………………………………………………………………………………….. 7
Discussion …………………………………………………………………………………………… 8
Kinematics and Kinetics …………………………………………………………………….. 8
Gait Patterns ………………………………………………………………………………… 9
Special Purpose Devices ……………………………………………………………………. 11
Muscle Strength and Compensation ………………………………………………………… 11
Soft Tissues ………………………………………………………………………………….. 13
Flexibility ……………………………………………………………………………………. 13
Limitations to the Study …………………………………………………………………….. 14
Concluding Thoughts ……………………………………………………………………….. 14
Appendix …………………………………………………………………………………………….. 16
Diagrams …………………………………………………………………………………………….. 18
References …………………………………………………………………………………………… 24

Introduction
Why is the incidence of hamstring strains high among sprinters? Among high school,
college, and professional track athletes, hamstring strains are common injuries that require
time off from practice and meets for recovery. This acute injury can lead to chronic pain and
reduced performance; therefore, hamstring strains can be detrimental to an athlete’s career and
a team’s success. Research studies have examined risk factors for hamstring strains, as well as
the mechanics of sprinting, and proper treatment for hamstring strains; however, the
mechanics of hamstring injury are still misunderstood. When investigating the causes of an
injury, it is necessary to consider potential risk factors, which include age, improper warm up,
flexibility, muscle weakness, and previous injuries. Hamstring strain can result from high
demand activities where the muscles experience abnormal stress and must produce substantial
forces. Results from a study conducted by Lempainen, L., Banke, I.J., Johansson, K., Brucker,
P.U., Sarimo, J., Orava, S., & Imhoff, A.B., suggest “previous hamstring injury displays the
greatest risk factor with 2–6 times elevated re-injury rates (2015).” Since incidence and
recurrence rates of hamstring strains are high, proper prevention and rehabilitation programs
are necessary to decrease the rates.
In addition to risk factors, it is essential to understand the mechanics of sprinting to
determine the underlying causes of hamstring strains. Hamstrings are mainly active during
terminal swing and early stance of the sprinting cycle. According to Schache A.G., Kim, H.,
Morgan, D.L., & Pandy, M.G., hamstring length and force were greatest when sprinting and
lowest when walking. Also, hamstring load was greatest when hip extension and knee flexion

torques were produced during terminal swing of sprinting (2010). Comprehending the risk
factors and how they change the mechanics of the body when sprinting will explain the cause
of injury and can unfold preventative measures.
There has been limited success in reducing the rate of recurrence of hamstring strains.
Current rehabilitation programs involving strength training and short recovery time may not be
sufficient healing time for the hamstrings and can cause recurrence of the injury when the
athlete returns back to their sport. Studies have tested various rehabilitation programs, such as
isolated hamstring stretching and strengthening and trunk stabilization; however, research
does not recommend one effective program. Heiderschiet et al found hamstring strains reoccur
when there is “persistent weakness in the injured muscle, reduced extensibility of the
musculotendon unit due to residual scar tissue, and adaptive changes in the biomechanics and
motor patterns of sporting movements following the original injury (2010).” Since most
injuries among sprinters comprise of hamstring strains, investigating the causes and effects of
these strains could help indicate the risk factors associated, as well as identify the mechanics
of the muscles during high demand and high power activities such as sprinting. Throughout
this paper the hamstring muscles are referred to numerous times; let it be known that when
referring to the group of hamstring muscles, it is implied that this group is comprised of the
semimembranosus, semitendinosus, and biceps femoris long head and short, although special
attention will be given to the biceps femoris long head. Results of the experiments in this
paper will allow for a rehabilitation and prevention program that is specific to the mechanism
of injury.

Methods
First, a literature review was conducted to recognize the incidence of hamstring strains
among college athletes, to identify predisposing risk factors, and to explore current findings
regarding the causes and treatment of the injury. Peer reviewed articles were found using
databases such as Google Scholar and PubMed through Boston University’s library resources.
Second, various tests were conducted on two subjects who volunteered to participate in
the study. During the study, age and sex were adjusted for; both subjects were 20-year-old
females on the Boston University Track and Field team. Subject A is a long-distance runner
with no history of this injury and subject B is a sprinter with history of multiple hamstring
strains. Subjects were aware of test procedures and all data were gathered at Boston
University’s Track and Tennis Center.
Range of motion was tested to assess hamstring flexibility and tightness. Subjects laid
in the supine position on a level surface and a goniometer was used to take degree
measurements. Both right and left sides of the lower extremity were individually tested and
measured three times. The leg was actively moved to 90-degree hip flexion and full knee
extension. One observer applied force just above the knee of the resting leg and behind the
ankle of the extended knee to ensure accurate measurements of the angles.
Using an iPhone 6S iSight camera, video and photos were taken in the sagittal plane of
the subjects during each experiment. The camera captures 12 megapixel still photos and takes
slow motion videos in 720p at 240 frames per second. Both subjects dynamically stretched
before the experiment for 10 minutes to increase their heart rate. Dynamic stretches consisted

of lunges, high knees, and leg swings. After warm up, each subject walked 20 meters at their
preferred stride frequency and sprinted 20 meters at submaximal velocities. Gait patterns were
observed and analyzed for each subject while walking and sprinting. Degrees of knee flexion
and extension, hip flexion and extension, and foot plantarflexion and dorsiflexion were
included in the observations. Comparisons were made between the two modes of locomotion.
In addition, hamstring strength tests were conducted at Boston University’s Fitness and
Recreation Center. The prone leg curl machine was used to estimate one repetition maximum
(1RM). Subjects laid prone on the machine with slight hip flexion and a bar at the ankles.
Subjects contracted their hamstrings to curl the bar. The formula used to estimate 1RM is one
plus the number of repetitions divided by thirty multiplied by the mass of the weight lifted
(Figure 4). A mass of 18.2 kilograms was lifted for 18 repetitions, meaning that the indirect
1RM is 29.12 kg.
After the experiments were conducted, the videos and photos were analyzed using the
Dartfish motion analyzer application for iPhones. Forces were sketched and named on the
experimental photographs. The sketches were translated into free body diagrams to
demonstrate the moment arms and forces during walking and sprinting. In addition, the
photographs were used to measure segmental lengths and angles of each subject. Segmental
mass and centers of mass were estimated using anthropometric table. Comparisons were made
between the two subjects.

Results
Prior to conducting any experiments, subject data was gathered, which included age,
height, total body mass, total leg mass, mass of the thigh, length of the biceps femoris, and
history of hamstring injury. Both subjects were 20-year-old females on the Boston University
Track and Field team. Subject A was a long-distance runner who had never experienced
hamstring injuries, and subject B was a sprinter, who had more than three hamstring injuries
on each leg. As shown in Figure 1, Subject A was 65 centimeters tall and had a total body
mass of 61.4 kilograms. Subject A’s total leg mass was 9.88 kilograms, while the mass of her
thigh was 6.14 kilograms and the length of her biceps femoris was 39.5 centimeters. Subject
B, on the other hand, was 67 centimeters tall and had a total body mass of 62.3 kilograms.
Subject B’s total leg mass was 10.03 kilograms, the mass of her thigh was 6.23 kilograms, and
the length of her biceps femoris was 44 centimeters.
Several experiments were conducted in order to achieve optimal and accurate results
regarding hamstring strains; these experiments included walking examinations, sprinting
examinations, hamstring flexibility evaluations, and hamstring maximal strength evaluations.
Experimenters decided to measure knee flexion length during the walking and sprinting
examinations. During the early stance of walking, subject A had a knee flexion angle of 169
degrees, while subject B had a knee flexion angle of 172 degrees. In the terminal swing phase
of walking, subject A had a knee flexion angle of 100 degrees, while subject B had a knee
flexion angle of 110 degrees. The difference between the terminal swing angle and early
stance angle for subject A was 69 degrees, while the difference for subject B was 62 degrees

(See Figure 2). Additionally, during the early stance of sprinting, subject A had a knee flexion
angle of 141 degrees, while subject B had a knee flexion angle of 144 degrees. However,
during the terminal swing stance of sprinting, subject A had a knee flexion angle of 138
degrees, while subject B had a knee flexion angle of 142 degrees. During this part of the study,
experimenters found that subject B, who was very susceptible to hamstring injuries, had
greater knee flexion angles during the early stances of both walking and sprinting. In addition,
Subject B had a greater anterior pelvic tilt of 53 degrees when sprinting compared to 42
degrees when walking. Subject A had an anterior pelvic tilt of 31 degrees when walking and
43-degree tilt when sprinting.
Discussion
Kinematics and Kinetics
Throughout the sprinting gait cycle, the tension acting on the hamstrings varies
depending on the stance of the leg. The hamstrings can absorb power while eccentrically
contracting or they can generate power while concentrically contracting. Muscular injuries can
occur when a muscle is actively contracting while being passively stretched. This could in fact
be a potential mechanism for subject B’s repeated hamstring injuries.
In every phase of sprinting, the joint reaction force, ground reaction force, and force of
body weight determine the torques the muscles must produce to prevent collapse of the body.
In fact, the ground reaction force is larger when running because the torques required to
activate the spring special purpose device in the hamstrings is significantly greater due to the
stiffness of the actively contracting muscle.

Additionally, the types of contractions of each muscle change during each phase and
have the potential to make muscles more susceptible to injury. During concentric contraction,
the muscle is shortened while generating power. On the other hand, when muscles
eccentrically contract, the muscles are lengthened and absorb power. During early stance to
push off, the gastrocnemius muscle concentrically plantarflexes the foot while the quadriceps
concentrically extend the knee. During early to mid-swing of sprinting, concentric
contractions are occurring as the hamstrings flex the knee and the gluteus maximus flexes the
hip. In the terminal swing phase of sprinting, subject B’s center of mass was in front of her
pelvis and her body’s momentum accelerated her body forward. At this phase, the knee is
descending to transition into early stance where the knee is extended. Therefore, the
hamstrings transition from a concentric to an eccentric contraction. The hamstrings
eccentrically contract to prevent rapid and excessive knee extension.
During sprinting, forces are drastically higher than walking since the bodily
acceleration is much higher. Consequently, when subject B sprinted during the experiment,
her hamstring muscle eccentrically contracted at a faster rate during the terminal swing phase
and experienced more tension. This increased stress put the subject at a greater risk for
musculotendon injuries (See Figure 4).
Gait Patterns
While analyzing the walking and sprinting gait patterns of both subjects A and B, more
differences than similarities were identified. While walking, there was a significant difference
found between subjects in regards to knee flexion angles at initial stance and during terminal

swing. By utilizing all three dynamic resources, spring, escapement, and inverted pendulum,
the subjects walked at their preferred stride frequency, thus minimizing their metabolic cost
and muscle force. At initial stance, the foot pronates, thus creating internal rotation of the tibia
via the talocrural joint anatomy. This internal rotation forces the knee into flexion and at the
same time, forces the femur to internally rotate. The hamstring muscles eccentrically contract
during the early stance phase, preventing full flexion of the knee and aiding the quadriceps
muscles in knee extension. It is important to note that the biceps femoris is responsible for
creating flexion around the knee joint and extending the femur posteriorly in the acetabulum.
When the subjects sprinted, there was a significant difference between both early
stance angles as well as terminal swing angles. Subject A had an early stance knee flexion
angle of 141 degrees, while subject B had an early stance knee flexion angle of 144 degrees.
Subject B’s larger angle, although seemingly insignificant, indicates that her hamstrings are
being stretched further, which puts the subject at a greater risk for hamstring muscle and
tendon injuries, particularly closer to the biceps femoris’ insertion at the fibular head.
Similarly, during the terminal swing phase, subject B had a knee flexion angle of 146 degrees,
while subject A had a knee flexion angle of 138 degrees. Subject B’s greater angle during the
terminal swing phase once again puts her at a greater risk for hamstring injuries because her
muscle is being stretched further while eccentrically contracting at a high force.
Closer examination of the origin of the biceps femoris long head, the ischial tuberosity,
indicated that anterior pelvic tilt also influences the degree of tension on this muscle. Due to
an increased anterior pelvic tilt at early stance during walking and sprinting, subject B is at

greater risk for a hamstring injury. Tension at both ends of this muscle, due to a greater angle
of extension at the knee and a greater angle of anterior pelvic tilt, while the muscle is
contracting increases the risk of injury to either the tendons that attach the hamstring muscles
to the bone, or to the muscle itself.
Special Purpose Devices
While sprinting, individuals use their legs as springs, a special purpose device which
takes advantage of the elastic properties in their muscles, tendons, ligaments, and fascia. This
allows the individual to gain more momentum while running, which will propel their body
forward at a faster rate. The spring energy must be released at the right state during the
sprinting gait cycle. If it is not properly used, energy will not be conserved. However, the
hamstrings not only function as springs while sprinting, they also function as dampers that
absorb energy. Timing must be precise during the sprinting cycle to ensure that elastic energy
is put into the system and conserved. Inserting energy into the system at the right time allows
for the optimal sprinting gait and could potentially prevent detrimental muscular injuries.
Muscle Strength and Compensation
Muscle weaknesses, especially contralateral imbalances, have been an undisputed risk
factor leading to injury. Therefore, it is suggested that subject B strengthen her posterior
thoracic and lumbar muscles, gluteal muscles, and her gastrocnemius and soleus muscles.
Strengthening Subject B’s erector spinae muscles will likely prevent further pelvic tilt, thus
reducing the pull on the hamstrings muscles at the point of origin. In order to strengthen the

subject’s lumbar muscles, specifically her erector spinae muscles, “bird dog” exercises and
back raises are recommended.
Strengthening the gluteus maximus, a hip extensor, will further resist anterior pelvic
tilt. Since the gluteus maximus is responsible for hip extension, a weak gluteus maximus could
cause an overuse injury in the hamstring muscles due to overcompensation. Performing glute
bridges, single or double leg squats, lunges, and a variety of other exercises can strengthen the
gluteus maximus. Additionally, strengthening the gastrocnemius muscle would aid in the
flexion of the knee, thus decreasing the likelihood of an overuse injury to the hamstring.
Increasing subject B’s knee flexion will decrease the moment arm of the lower leg by moving
the center of mass closer to the axis of rotation. Less force will need to be exerted by the
hamstrings, also helping to prevent more hamstring overuse injuries in subject B.
It was unclear, based on initial testing of Subject A and B’s hamstring strength, if
weakness was a predisposing element to hamstring strain. The test subjects had negligible
differences, a difference of 6.45%, between their one repetition maximum when performing
double-leg hamstring curls. After performing a bilateral strength comparison test, it became
more evident what that bilateral muscle imbalance is predisposing risk factor. Research has
demonstrated that “subjects with greater than 10% hamstring muscle strength imbalance are
more likely to suffer hamstring muscle strain.” (Patton, S. B., 1996). Subject B demonstrated a
difference of 7.4% between her 1-RM of her left and right hamstrings. Although this percent
difference is not as high as the 10% difference mentioned by Scottie B. Patton (1996),

lessening the bilateral imbalance by strengthening her right hamstring would serve as a
lucrative tool in preventing additional hamstring strains.
Soft Tissues
Muscle strengthening is not the only way to prevent hamstring injury. Built up scar
tissue from previous injuries to the subject’s hamstrings could be eliminated using soft tissue
instrument assisted mobilization, otherwise known as the Graston technique. This technique
would be advantageous, allowing for proper expansion, contraction, and relaxation of the
muscle and surrounding soft tissues. Limited range of motion of the hamstring due to scar
tissue formation creates an added potential for injury; the muscle will be stretched to capacity
at an earlier point than it had been able to stretch prior to scar tissue formation. Without full
range of motion, the risk of straining the muscle increases and in this way, a cycle of
hamstring strains and scar tissue formation transpires.
Flexibility
Research has been inconclusive in regards to the influence of flexibility in preventing
muscle strains. Some studies have shown that increasing the resting length of a muscle could
reduce some injuries by increasing the amount of force a muscle could withstand (Jamtvedt,
G., Herbert, R., Flottorp, S., Odgaard-Jensen, J., Havelsrud, K., Barratt, A., Mathieu, E., Burls,
A., & Oxman, A., 2010, 378). In the study conducted with subject A and subject B, flexibility
remains inconclusive as a precursor to hamstring injury, as the two subjects had negligible
differences between their pelvic ranges of motion and hamstring flexibility. Although

stretching prior to exercise will increase an athlete’s immediate range of motion and range of
sarcomere stretch, it will likely not prevent injury.
Limitations to the Study
One limitation of the study conducted on subject A and subject B is that the subjects
were not monitored for potential hamstring injuries during the course of their running careers.
If the study was conducted longitudinally, researchers would have been able to correct subject
B’s form while sprinting and could have potentially prevented her recurrent hamstring strains.
Moreover, despite conducting this study at the Boston University Track and Tennis Center
with iPhone 6S technology, results could have been more accurate had they been conducted in
a professional laboratory setting with more complex, precise, and advanced technological
equipment. Additionally, our group was unable to calculate the ground reaction forces of both
subject A and subject B. This is primarily because we did not have the proper equipment, such
as force plates and position markers, to detect such measurements. However, by calculating
the ground reaction forces, a multi-link free body diagram could have been used to determine
the joint reaction forces being exerted on the knee and the hip of subject A and subject B.
Concluding Thoughts
Hamstring injuries are quite common, especially among elite runners, but they have the
potential to be prevented. Our findings from our experiments suggest several potential causes
for hamstring injury, including muscle weaknesses, muscle imbalances, timing errors, poor
running form, and scar tissue buildup. To prevent the pain and future consequences of a
hamstring strain, our experiments have reaffirmed, from existing research, that eccentrically

strengthening the hamstrings and training nearby muscles will significantly reduce the stress
and strain acting on this injury-susceptible muscle. Additionally, our findings suggest that
hamstring injuries can occur during the transition between the terminal swing and early stance
phases of sprinting. This timing error between phases causes the hamstrings to actively
contract while being passively stretched under extreme loads, thus putting the athlete at a
greater risk of hamstring strain. Using a combination of prevention and rehabilitation
treatments, the career-altering and painful effects of hamstring strains could be deterred.

Appendix
FIGURE 1:
FIGURE 2:
FIGURE 3:

FIGURE 4:

Diagrams
Free Body Diagrams:
Sprinting— Terminal Swing
Walking— Heel Strike

Motion Capture Free Body Diagrams:
Subject A Sprinting— Late Stance Subject A Sprinting— Terminal Swing
Subject A Walking— Push Off Subject A Walking— Heel Strike

Subject A Sprinting— Terminal Swing Angle
Subject A Sprinting— Pelvic Tilt Angle Subject B Walking— Pelvic Tilt Angle
Subject A Walking— Terminal Swing Angle

Subject B Sprinting— Late Stance Subject B Sprinting— Terminal Swing
Subject B Walking— Push Off Subject B Walking— Heel Strike

Subject B Sprinting— Terminal Swing Angle
Subject B Sprinting— Pelvic Tilt Angle Subject B Walking— Pelvic Tilt Angle
Subject B Walking— Terminal Swing Angle

References
Hederscheit, B., Sherry, M.A., Silder, A., Chumanov, E.S., & Thelen, D.G. (2010).
Hamstring Strain Injuries: Recommendations for Diagnosis, Rehabilitation, and Injury
Prevention. Journal of Orthopaedic and Sports Physical Therapy 40(2), 67-69.
Retrieved from: http://www.jospt.org/doi/pdf/10.2519/jospt.2010.3047
Jamtvedt, G., Herbert, R., Flottorp, S., Odgaard-Jensen, J., Havelsrud, K., Barratt, A.,
Mathieu, E., Burls, A., & Oxman, A. (2010). A Pragmatic Randomised Trial of
Stretching Before and After Physical Activity to Prevent Injury and Soreness. Journal
of Science and Medicine in Sport 12: 378. doi: 10.1016/j.jsams.2009.10.378.
Lempainen, L., Banke, I.J., Johansson, K., Brucker, P.U., Sarimo, J., Orava, S., &
Imhoff, A.B. (2015). Clinical Principles in the Management of Hamstring Injuries.
PubMed. Knee Surg Sports Traumatol Arthrosc., 23(8): 2449-2456. doi:
10.1007/s00167-014-2912-x.
Patton, S. B. (1996). Factors that Predispose Hamstring Muscle Strain (Order No. 1379367).
Available from ProQuest Dissertations & Theses Global. (304355147). Retrieved from
http://search.proquest.com/docview/304355147?accountid=9676
Schache, A.G., Kim, H., Morgan, D.L., & Pandy, M.G. (2010). Hamstring Muscle Forces
Prior To and Immediately Following an Acute Sprinting-Related Muscle Strain Injury.
Department of Mechanical Engineering, University of Melbourne, Victoria, Australia,
32(1): 136-140. doi: 10.1016/j.gaitpost.2010.03.006.

Hamstring Strains Project- FINAL!

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