Validity and reliability of a new test of lower leg musculotendinous ...

Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
Introduction
Musculotendinous stiffness (MTS) plays an integral role in both determination of injury risk and performance. Research examining this physiological
component has been relatively abundant over the past decade, however, new assessment devices are required to enable assessment of
different muscle groups. MTS is dependent on body location and training status of the athlete (Wilson et al., 1992; Walshe et al., 1996), hence,
the response may vary on an individual level. The role of MTS in performance is well documented (Wilson et al., 1991; 1992; 1994; Walshe &
Wilson, 1997), however, conflicting ideas are evident in the literature (Komi et al., 1984; Walshe & Wilson, 1997). When examining performance,
a relatively stiffer system has been shown to be more beneficial from a force-velocity perspective (Wilson et al., 1992; 1994), where rapid force
generation and application within the muscle is required. On the other hand, it has been shown that a more compliant system is optimal during
the performance of relatively slower activities (Walshe & Wilson, 1997). It is argued that a more compliant muscle is able to generate more
force through the ability to permit a greater storage of elastic strain energy due to the ability to elongate to greater distances during the eccentric
phase of such actions. Despite this research, the role of MTS in injury risk is far more inconclusive. It is thought that a relatively stiffer system
results in a greater injury risk, whereas a more compliant system is better able to conform to the elongation resulting from different movement
patterns and dissipate the force developed within the musculotendinous unit over a greater time, hence maximising the impulse.
Previous research findings strongly indicate that the properties of the muscle-tendon unit are directly related to successful athletic performance
in a number of arenas. This fact, along with the scarcity of conclusive research in the area of muscular stiffness and flexibility indicate the
importance of research in this area. The need to identify valid and reliable testing procedures to assess MTS is clear.
Methods
This study was carried out in the Human Performance Laboratory at the University of Technology, Sydney and involved the examination of the
MTS of the triceps surae of 20 male subjects. The triceps surae refers to the muscle pair of the gastrocnemius and the soleus, which shape the
posterior calf, and insert, via the achilles tendon, into the calcaneous of the foot. Other functional measures including maximal isometric
strength (MIS), rate of force development (RFD), power and reactive strength were also assessed in order to determine any relationships with
MTS.
An instrumented calf raise machine able to measure MIS, RFD and MTS of the triceps surae was designed and constructed for the purposes
of this study. The two testing occasions were separated by no more than 7 days, during which time the participants were instructed to maintain
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Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
their normal activity levels. Subjects were asked to refrain from vigorous lower body exercise in the twenty-four hours preceding their assessment.
To decrease any risk of injury, a standardised warm-up protocol was administered to all subjects.
Maximal Isometric Strength and Rate of Force Development
Assessment of triceps surae strength was performed using a maximal isometric contraction. The bar height and position over the knees was
standardised for each participant. Different lower leg lengths were taken into consideration for each participant courtesy of a multi-link chain,
enabling links to be added and removed as required. The test was performed without shoes to avoid any inter-shoe cushioning variability and
to negate any cushioning that may alter the RFD. As an injury prevention measure, high-density foam (20 mm thick) was placed on the foot
platforms. The participants were placed in an upright position with arms folded across the chest and were instructed to produce force as hard
and as quickly as possible and to hold it for 3 seconds. Force data were recorded at 1000 Hz by a load cell (Chase Engineering, Sydney,
Australia), which was positioned between the ground and the movable arm of the calf raise machine. Two trials were conducted at each session
with rest allocated between trials, and the average of the trials was used for all force results. Verbal encouragement was given for each test.
From this data, the peak force and maximum RFD (5 ms average) were measured and analysed.
Musculotendinous stiffness: Assessment of musculotendinous stiffness was performed using the oscillation technique. The position for the
participant was identical to that used for isometric force assessment. The chosen position isolated the triceps surae musculature, hence
allowing the relationship between stiffness and force in the triceps surae to be examined. The oscillation technique involves the assumption
that human muscle is modelled as a damped spring system and that any perturbation to a loaded system will result in oscillations containing a
damping element due to the nature of the muscle and tendon. This valid and reliable technique has been used on numerous occasions
(Cavagna, 1970; McNair & Stanley, 1996; Shorten, 1987; Wilson et al., 1991; 1992; 1994; Walshe & Wilson, 1997). The current study however,
utilised a new machine for assessment of validity and reliability which minimises the variance evident in multi-joint movements through isolating
the triceps surae.
The present study isolated the lower leg for musculotendinous stiffness assessment, in an identical position represented by Shorten (1987).
Assessment of MIS was performed in the same position as MTS assessment in an attempt to make the tests as specific as possible.
The participants supported a load utilising the triceps surae musculature and maintained a 90º angle at the ankle. This involved the knee being
placed at an angle of approximately 90º. Whilst this position may not allow for complete activation of the gastrocnemius musculature, assessment
of the musculotendinous unit involving the triceps surae/achilles tendon is still appropriate.
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Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
A brief perturbation was then applied and the ensuing oscillations were recorded. The perturbation was to the order of 100 N– 200 N, however,
slight variations in the magnitude do not have a negative effect on the results. According to Shorten (1987), Wilson et al. (1991, 1992, 1994)
and Walshe & Wilson (1997) the system will oscillate at its natural frequency regardless of the magnitude of the perturbation. An example of
these oscillations is portrayed in Figure 1. A ‘do not intervene’ strategy was employed by the participants upon administration of the perturbation.
This negated any voluntary muscular contractions which, if present, alter the waveform of the oscillations, resulting in corrupted data. As a
result, the participants were instructed to attempt to retain an identical ankle joint angle for the duration of the oscillations, however, not to
additionally contract the muscle in an effort to achieve this.
Figure 1. Representation of resultant damped oscillations following
Figure 1. Representation of resultant damped oscillations following the application of the perturbation.
Various loads were added to the calf raise machine for assessment. These were the equivalent of 50%, 100%, and 200% of body mass (BM)
at the point of force transmission to the lower leg. Loads related to BM were chosen as it was deemed more relevant to the lower body
musculotendinous system, as opposed to the upper body systems measured in previous research (Wilson et al., 1991; 1992; 1994). The data
was passed through a low pass Butterworth filter (4 th order) with a cut-off frequency of 12 Hz and stored for processing. For each load, two trials
were completed and averaged for each testing session. Rest periods of 2-3 mins were designated between all trials.
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Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
Statistical Analysis: SPSS (Statistical Package for the Social Sciences) version 9 was used to analyse any relationships between stiff and
compliant musculotendinous units, and the resulting performance outputs. In order to examine test-retest reliability, intraclass correlations
were performed to determine if any significant differences existed between the data from the two testing occasions. Correlations were also
conducted on the 200% BM stiffness data. For the validity analysis, subjects were broken into two groups; the 10 most compliant and the 10
stiffest subjects. Results from the two groups were then averaged and paired t-tests carried out on the mean values. Probability was set at
p

Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
Conclusion
As eluded to by previous research, MTS plays an integral role in performance (Wilson et al., 1994). The results of the current study are in
concurrence with the previous research, showing that a relatively stiff musculotendinous system permits superior performance in RFD activities.
Previous research has attributed this ability to improved length-tension and force-velocity conditions of contraction.
Regardless of these performance implications, further research is required to examine the role of MTS and injury risk. Theoretically, an
increase in stiffness leads to an increased injury risk through less force dissipation ability and a smaller distance over which to absorb the force
following either internal or external force application.
The current research suggests that there is a strong relationship between stiffness and RFD. Therefore, according to the hypothesis suggested,
individuals with high RFD capabilities may be at a greater risk of sustaining a soft tissue injury. Therefore, an optimal stiffness of the muscle
exists, with different sports requiring different levels of MTS for optimal performance. The continuum of relatively stiff vs. relatively compliant
musculotendinous units has been examined previously by Wilson et al. (1994) who found that for relatively slow SSC activities (>300ms), a
more compliant musculotendinous stiffness system was more beneficial due to an enhanced ability to store elastic strain energy. However for
relatively fast SSC activities (100 – 150ms), a stiffer system was more beneficial for performance due to factors outlined earlier in this paper.
Figure 2. The relationship between the two testing
occasions. Correlational analysis revealed no
significant differences between test 1 and test 2.
Test 1
Stiffness (N/m)
12000
10000
8000
6000
4000
2000
0
0 2000 4000 6000 8000 10000 12000
Stiffness (N/m)
Test 2
Figure 2. The relationship between the two testing occasions. Correlational analysis re
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Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie University of Technology, Sydney, Australia
References
Bach, T.M., Chapman, A.E. & Calvert, T.W. (1983). Mechanical resonance of the human body during voluntary oscillations about the ankle joint.
Journal of Biomechanics, 16, 85-90.
Cavagna, G. (1970). Elastic bounce of the body. Journal of Applied Physiology, 29, 279-282.
McNair, P.J. & Stanley, S. (1996). The effect of passive stretching and jogging on the series elastic muscle stiffness and range of movement at
the ankle joint. British Journal of Sports Medicine, 30, 313-318.
Safran, M., William, G., Seaber, A., Glisson, R. & Ribbeck, B. (1988). The role of warmup in muscular injury prevention. The American Journal
of Sports Medicine, 16, 123-129.
Shorten, M.R. (1987). Muscle elasticity and human performance. Medicine and Sport Science, 25, 1-18.
Walshe, A.D., Wilson, G.J. & Murphy, A.J. (1996). The validity and reliability of a test of lower body musculotendinous stiffness. European
Journal of Applied physiology, 73, 332-339.
Walshe, A.D. & Wilson, G.J. (1997). The influence of musculotendinous stiffness on drop jump performance. Canadian Journal of Applied
Physiology, 22, 117-132.
Wilson, G.J., Wood, G.A. & Elliot, B.C. (1991). Optimal stiffness of the series elastic component in a stretch shorten cycle activity. Journal of
Applied physiology, 70, 825-833.
Wilson, G.J., Elliot, B.C. & Wood, G.A. (1992). Stretch shorten cycle performance enhancement through flexibility training. Medicine and
Science in Sports and Exercise, 24, 116-123.
Wilson, G.J., Murphy, A.J. & Pryor, J. (1994). Musculotendinous stiffness: its relationship to eccentric, isometric and concentric performance.
Journal of Applied Physiology, 76, 2714-2719.
Print
Index
Table of Contents
Quit

Validity and reliability of a new test of lower leg musculotendinous stiffness
M.J. Pine*, A.J. Murphy, M.L. Watsford, R.W. Spurrs, R.S. Lockie
University of Technology, Sydney, Australia
INTRODUCTION: Musculotendinous stiffness (MTS) plays an integral role in both determination of injury risk and
performance. Research examining this physiological component has been relatively abundant over the past decade,
however, new assessment devices are required to enable assessment of different muscle groups. MTS is dependent on
body location and training status of the athlete (Wilson et al., 1992; Walshe et al., 1996), hence, the response may vary on
an individual level. The role of MTS in performance is well documented (Wilson et al., 1991; 1992; 1994; Walshe & Wilson,
1997), however, conflicting ideas are evident in the literature (Komi et al., 1984; Walshe & Wilson, 1997). When examining
performance, a relatively stiffer system has been shown to be more beneficial from a force-velocity perspective (Wilson et
al., 1992; 1994), where rapid force generation and application within the muscle is required. On the other hand, it has been
shown that a more compliant system is optimal during the performance of relatively slower activities (Walshe & Wilson,
1997). It is argued that a more compliant muscle is able to generate more force through the ability to permit a greater
storage of elastic strain energy due to the ability to elongate to greater distances during the eccentric phase of such actions.
Despite this research, the role of MTS in injury risk is far more inconclusive. It is thought that a relatively stiffer system
results in a greater injury risk, whereas a more compliant system is better able to conform to the elongation resulting from
different movement patterns and dissipate the force developed within the musculotendinous unit over a greater time, hence
maximising the impulse.
Previous research findings strongly indicate that the properties of the muscle-tendon unit are directly related to
successful athletic performance in a number of arenas. This fact, along with the scarcity of conclusive research in the area
of muscular stiffness and flexibility indicate the importance of research in this area. The need to identify valid and reliable
testing procedures to assess MTS is clear.
METHODS: This study was carried out in the Human Performance Laboratory at the University of Technology, Sydney
and involved the examination of the MTS of the triceps surae of 20 male subjects. The triceps surae refers to the muscle
pair of the gastrocnemius and the soleus, which shape the posterior calf, and insert, via the achilles tendon, into the
calcaneous of the foot. Other functional measures including maximal isometric strength (MIS), rate of force development
(RFD), power and reactive strength were also assessed in order to determine any relationships with MTS.
An instrumented calf raise machine able to measure MIS, RFD and MTS of the triceps surae was designed and
constructed for the purposes of this study. The two testing occasions were separated by no more than 7 days, during which
time the participants were instructed to maintain their normal activity levels. Subjects were asked to refrain from vigorous
lower body exercise in the twenty-four hours preceding their assessment. To decrease any risk of injury, a standardised
warm-up protocol was administered to all subjects.
Maximal Isometric Strength and Rate of Force Development
Assessment of triceps surae strength was performed using a maximal isometric contraction. The bar height and position
over the knees was standardised for each participant. Different lower leg lengths were taken into consideration for each
participant courtesy of a multi-link chain, enabling links to be added and removed as required. The test was performed
without shoes to avoid any inter-shoe cushioning variability and to negate any cushioning that may alter the RFD. As an
injury prevention measure, high-density foam (20 mm thick) was placed on the foot platforms. The participants were placed
in an upright position with arms folded across the chest and were instructed to produce force as hard and as quickly as
possible and to hold it for 3 seconds. Force data were recorded at 1000 Hz by a load cell (Chase Engineering, Sydney,
Australia), which was positioned between the ground and the movable arm of the calf raise machine. Two trials were
conducted at each session with rest allocated between trials, and the average of the trials was used for all force results.
Verbal encouragement was given for each test. From this data, the peak force and maximum RFD (5 ms average) were
measured and analysed.
Musculotendinous stiffness: Assessment of musculotendinous stiffness was performed using the oscillation technique.
The position for the participant was identical to that used for isometric force assessment. The chosen position isolated the
triceps surae musculature, hence allowing the relationship between stiffness and force in the triceps surae to be examined.
The oscillation technique involves the assumption that human muscle is modelled as a damped spring system and that any
perturbation to a loaded system will result in oscillations containing a damping element due to the nature of the muscle and
tendon. This valid and reliable technique has been used on numerous occasions (Cavagna, 1970; McNair & Stanley, 1996;
Shorten, 1987; Wilson et al., 1991; 1992; 1994; Walshe & Wilson, 1997). The current study however, utilised a new

machine for assessment of validity and reliability which minimises the variance evident in multi-joint movements through
isolating the triceps surae.
The present study isolated the lower leg for musculotendinous stiffness assessment, in an identical position represented
by Shorten (1987). Assessment of MIS was performed in the same position as MTS assessment in an attempt to make the
tests as specific as possible.
The participants supported a load utilising the triceps surae musculature and maintained a 90º angle at the ankle. This
involved the knee being placed at an angle of approximately 90º. Whilst this position may not allow for complete activation
of the gastrocnemius musculature, assessment of the musculotendinous unit involving the triceps surae/achilles tendon is
still appropriate.
A brief perturbation was then applied and the ensuing oscillations were recorded. The perturbation was to the order of
100 N – 200 N, however, slight variations in the magnitude do not have a negative effect on the results. According to
Shorten (1987), Wilson et al. (1991, 1992, 1994) and Walshe & Wilson (1997) the system will oscillate at its natural
frequency regardless of the magnitude of the perturbation. An example of these oscillations is portrayed in Figure 1. A ‘do
not intervene’ strategy was employed by the participants upon administration of the perturbation. This negated any
voluntary muscular contractions which, if present, alter the waveform of the oscillations, resulting in corrupted data. As a
result, the participants were instructed to attempt to retain an identical ankle joint angle for the duration of the oscillations,
however, not to additionally contract the muscle in an effort to achieve this.
Figure 1. Representation of resultant damped oscillations following the application of the perturbation.
Various loads were added to the calf raise machine for assessment. These were the equivalent of 50%, 100%, and
200% of body mass (BM) at the point of force transmission to the lower leg. Loads related to BM were chosen as it was
deemed more relevant to the lower body musculotendinous system, as opposed to the upper body systems measured in
previous research (Wilson et al., 1991; 1992; 1994). The data was passed through a low pass Butterworth filter (4 th order)
with a cut-off frequency of 12 Hz and stored for processing. For each load, two trials were completed and averaged for each
testing session. Rest periods of 2-3 mins were designated between all trials.
Statistical Analysis: SPSS (Statistical Package for the Social Sciences) version 9 was used to analyse any relationships
between stiff and compliant musculotendinous units, and the resulting performance outputs. In order to examine test-retest
reliability, intraclass correlations were performed to determine if any significant differences existed between the data from
the two testing occasions. Correlations were also conducted on the 200% BM stiffness data. For the validity analysis,
subjects were broken into two groups; the 10 most compliant and the 10 stiffest subjects. Results from the two groups
were then averaged and paired t-tests carried out on the mean values. Probability was set at p

Validity: The oscillation technique has been utilised by previous researchers (Cavagna, 1970; Wilson et al., 1991; 1992;
1994) and is a valid method of MTS assessment. Previous research has shown that a relationship exists between MTS and
RFD. Individuals exhibiting relatively stiffer musculotendinous units are able to achieve a greater RFD through improved
force-velocity and length-tension relationships (Wilson et al., 1991), while more compliant individuals exhibit smaller values.
Following the stiffness assessment, the subjects were divided into two groups made up of the four most compliant and the
four stiffest subjects. As hypothesised, significant differences were found between the stiff and the compliant groups in calf
stiffness (9652 N·m -1 vs. 6226 N·m -1 respectively) and in RFD (15364 N·s -1 vs. 11227 N·s -1 respectively) indicating that both
the stiffness and the RFD data attained was valid.
CONCLUSION: As eluded to by previous research, MTS plays an integral role in performance (Wilson et al., 1994). The
results of the current study are in concurrence with the previous research, showing that a relatively stiff musculotendinous
system permits superior performance in RFD activities. Previous research has attributed this ability to improved lengthtension
and force-velocity conditions of contraction.
Regardless of these performance implications, further research is required to examine the role of MTS and injury risk.
Theoretically, an increase in stiffness leads to an increased injury risk through less force dissipation ability and a smaller
distance over which to absorb the force following either internal or external force application.
The current research suggests that there is a strong relationship between stiffness and RFD. Therefore, according to
the hypothesis suggested, individuals with high RFD capabilities may be at a greater risk of sustaining a soft tissue injury.
Therefore, an optimal stiffness of the muscle exists, with different sports requiring different levels of MTS for optimal
performance. The continuum of relatively stiff vs. relatively compliant musculotendinous units has been examined
previously by Wilson et al. (1994) who found that for relatively slow SSC activities (>300ms), a more compliant
musculotendinous stiffness system was more beneficial due to an enhanced ability to store elastic strain energy. However
for relatively fast SSC activities (100 – 150ms), a stiffer system was more beneficial for performance due to factors outlined
earlier in this paper.
Test 1
Stiffness (N/m)
12000
10000
8000
6000
4000
2000
0
0 2000 4000 6000 8000 10000 12000
Stiffness (N/m)
Test 2
Figure 2. The relationship between the two testing occasions. Correlational analysis revealed no significant differences
between test 1 and test 2.
REFERENCES:
1. Bach, T.M., Chapman, A.E. & Calvert, T.W. (1983). Mechanical resonance of the human body during voluntary
oscillations about the ankle joint. Journal of Biomechanics, 16, 85-90.
2. Cavagna, G. (1970). Elastic bounce of the body. Journal of Applied Physiology, 29, 279-282.
3. McNair, P.J. & Stanley, S. (1996). The effect of passive stretching and jogging on the series elastic muscle
stiffness and range of movement at the ankle joint. British Journal of Sports Medicine, 30, 313-318.
4. Safran, M., William, G., Seaber, A., Glisson, R. & Ribbeck, B. (1988). The role of warmup in muscular injury
prevention. The American Journal of Sports Medicine, 16, 123-129.
5. Shorten, M.R. (1987). Muscle elasticity and human performance. Medicine and Sport Science, 25, 1-18.

6. Walshe, A.D., Wilson, G.J. & Murphy, A.J. (1996). The validity and reliability of a test of lower body
musculotendinous stiffness. European Journal of Applied physiology, 73, 332-339.
7. Walshe, A.D. & Wilson, G.J. (1997). The influence of musculotendinous stiffness on drop jump performance.
Canadian Journal of Applied Physiology, 22, 117-132.
8. Wilson, G.J., Wood, G.A. & Elliot, B.C. (1991). Optimal stiffness of the series elastic component in a stretch
shorten cycle activity. Journal of Applied physiology, 70, 825-833.
9. Wilson, G.J., Elliot, B.C. & Wood, G.A. (1992). Stretch shorten cycle performance enhancement through flexibility
training. Medicine and Science in Sports and Exercise, 24, 116-123.
10. Wilson, G.J., Murphy, A.J. & Pryor, J. (1994). Musculotendinous stiffness: its relationship to eccentric, isometric
and concentric performance. Journal of Applied Physiology, 76, 2714-2719.