Figure 6. Average Stiffness

1
Both passive and active warm-up are commonly used
to prevent hamstring injuries by lowering muscle
tension. However, active warm-up may be more
effective at preparing the muscle for stretching
and activity. The purpose of this pilot study
was to investigate the influence of active
warm-up and passive warm-up on hamstring passive
tension. Six male subjects were randomly
assigned to one of three treatment groups
(Control, Passive, Active). The passive warm-up
included a 15-min hot pack treatment and the
active warm-up performed stationary cycling at a
self-selected speed and workload at 60 heart
rate reserve for 3 min. Ten repetitions of
passive extension at a rate of 10º/sec for a
range of motion of 30º were induced using the
Biodex. From each knee extension, peak torque,
average stiffness and energy absorbed were
measured. Repeated measures ANOVAs (3 x 2) were
used to identify differences in treatment groups
and test (Pre, Post) for the dependent variables
stiffness, energy absorbed and peak torque (plt
0.05). There were no significant differences in
stiffness and peak torque between groups or test.
There was a significant difference between
pre-test energy 18.8 8.7 J and post-test energy
16.5 8.5 J. While not significant, exercise
reduced stiffness by 0.3 N/deg and passive
heating reduced stiffness by 0.12 N/deg. Because
there were no differences between treatment
groups, neither passive and active warm-up were
more effective then no warm-up. However, further
studies should investigate the influence of
familiarization trials on testing procedures.
The results for average torque by treatment
group are shown in Figure 4. There were no
significant differences between groups, pre
post, groups by pre post for average torque.
The results for energy absorbed are shown in
Figure 5. There were no significant differences
between groups, or groups by pre post for
energy absorbed . There was a significant
difference between pre-test energy 18.8 8.7 J
and post-test energy 16.5 8.5 J. The results
for average stiffness by treatment group are
shown in Figure 6. There were no significant
differences between groups, pre post, groups by
pre post for average torque.
Figure 1. Biodex Set-up
Figure 2. Typical trial of passive knee
extension on a Biodex Dynamometer.
Figure 3. Angular change was converted into
radians to allow energy to be calculated as area
covered by polynomial moment-angle curve. A
4th-order polynomial fit was applied to
moment-angle curve.
Figure 6. Average Stiffness Indicates
significant difference between pre and post
Subjects Six male college students (age 22
1.26 years, weight 153.58 23.5 lbs, height
67.67 1.78 in) volunteered to participate in
this pilot study and randomly assigned to one of
three treatment groups (control (n2), passive
(n2), active (n2)). The subjects completed a
health history questionnaire and consent form
before being allowed to participate in the study.
All of the subjects had less than 30 cm skinfold
test on the posterior thigh and supine 90/90 knee
extension less then 180o. Instrumentation A
Biodex system 3 (Biodex Medical Systems Inc.) was
used to determine hamstring passive tension.
Passive warm-up was achieved using heat packs
from a hydrocollator (Chattanooga Systems) and
active warm-up was performed on a Monark
stationary cycle ergometer. Skinfold calipers
were used to assess body fat of the subcutaneous
layers. Data Collection Each subject was
randomly assigned to one of the three treatment
groups. Upon arrival at the laboratory each
subjects age, height, weight, and skinfold
measurements were obtained. The subjects were
then placed in the supine position with the hip
and knee passively flexed to 90o. The subjects
knee was then passively extended until they
reported feeling a strong stretching sensation,
the angle was recorded at this point using a
goniometer. Next, the subjects were seated in
the Biodex and the knee passively extended until
the subject reported minimal discomfort
establishing the endpoint for testing (see Figure
1). Ten repetitions of passive extension were
then induced at a rate of 10o/sec for a range of
motion of 30o (see Figure 2). From each knee
extension, peak torque, average stiffness and
energy absorbed (see Figure 3) were measured.
After baseline measurements were obtained the
control group lay prone for 15 min. The passive
group lay prone for 15 min with a heat pack
placed on the belly of the biceps femoris. The
active groups resting heart rates were measured
then they performed stationary cycling at a
self-selected speed and workload at 60 heart
rate reserve for 3 min. Heart rate reserve (HRR)
was calculated using the following equation
target heat rate (HRR fraction)(HRmax HRrest)
HRrest. HRR fraction was chosen to be 60. At
the conclusion of treatment the subjects were
immediately reseated in the Biodex and retested
for passive tension following the pre-treatment
protocol. Data Analysis Repeated measure
ANOVAs (3 x 2) were used to identify differences
in treatment groups and test (Pre, Post) for the
dependent variables stiffness, energy absorbed
and peak torque (plt 0.05).
In the clinical athletic training setting active
and passive warm-ups are common modalities used
prior to stretching to improve muscle
flexibility. A rise in tissue temperature
increases visoelasticity, which promotes tissue
extensibility and reduces passive tension.
Previous research has reported that the
application of hot packs can raise quadriceps
intramuscular temperature at a depth of 2.0 cm up
to 1.0ºC (Wood and Knight 2004). Temperature
increases as the result of hot pack application
may be attributed to increases in cellular
metabolism. During exercise, increases in muscle
temperature may be attributed to the release of
energy during muscle contraction. Muscle
temperature at a depth of 10 30 mm from the
femur during 15 min of knee extension exercise
has been reported to increase temperature 2.0
3.2ºC (Kenny et al. 2003). Increases in muscle
temperature have been linked to increases in
collagen tissue elasticity (Starkey 2004), which
would improve muscle flexibility by reducing
passive tension. Even though active warm-up has
previously been shown to provide greater
increases in intramuscular temperature, the
results from this study showed no significant
difference between active and passive warm-up on
passive muscle tension. These findings raise
questions regarding the effectiveness of active
and passive warm-up on passive muscle tension.
However, this study was limited by sample size
and the lack of subject familiarization.
Figure 4. Average Torque Indicates significant
difference between pre and post.



Neither passive or active warm-up were more
effective then no warm-up, because there were no
differences between treatment groups. However,
further studies should investigate the influence
of familiarization trials and the use of a
crossover design.
Figure 5. Average Energy Indicates significant
difference between pre and post