The effects of passive warming on muscle injury

Effects of Self-myofascial Release Using a Foam Roller on Range of Motion and Morphological Changes in Muscle: A Crossover Study

ABSTRACT

Yoshimura, A, Inami, T, Schleip, R, Mineta, S, Shudo, K, and Hirose, N. Effects of self-myofascial release using a foam roller on range of motion and morphological changes in muscle: a crossover study. J Strength Cond Res 35(9): 2444-2450, 2021-Self-myofascial release using a foam roller (FR) is effective in improving range of motion (ROM) in at least some conditions. However, its mechanism is still unclear. Therefore, this study investigated potential acute muscle morphological changes after the FR intervention and aimed to clarify the mechanism of increases in ROM by the FR intervention. We hypothesized that the FR intervention may increase ROM because of changes in fascicle length (FL) and aponeurosis displacement. This crossover study, involving 22 male university students (21.5 ± 1.3 years, 170.6 ± 4.0 cm, and 64.1 ± 8.9 kg; mean ± SD), compared the FR intervention targeting the gastrocnemius muscle with the control trial. The outcome measures were maximum passive ankle ROM, morphology of the gastrocnemius muscle (FL and aponeurosis displacement) during passive ankle plantar flexor movement, degree of pain during the FR intervention, and sensation of the triceps surae muscle. Although ROM of both dorsiflexion and plantar flexion increased significantly after the FR intervention (p < 0.01), no significant differences were found in FL and aponeurosis displacement before and after the FR intervention. The mean perception of pain during the FR intervention was rated as "slightly uncomfortable," corresponding to a 2.3 ± 2.4-cm on a 9.5-cm visual analog scale. We found that the FR intervention did not influence the morphology of muscle. It is necessary to investigate other factors related to ROM as the next step of this study.

Altered muscle activation in agility dogs performing warm-up exercises: an acoustic myography study

Agility is physically demanding and dogs encounter a considerable risk of injury during training and competition. Pre-performance warm-up is used routinely among human athletes to prepare the tissues for these physical demands, but in canine sports evidence for effects of warm-up is lacking. The aim of this study was to investigate the effects of warm-up in dogs on two major muscles involved in locomotion. It was hypothesised that, after warm-up, the muscles would be used more efficiently (more fibre resting time/total time), recruit fewer fibres (reduced spatial summation) and/or activated with a lower firing frequency (reduced temporal summation). The following factors ‘sex, age, weight, height, training level and agility experience’ were evaluated for their potential impact on muscle function parameters. Fourteen large (≥46 cm at the withers) agility dogs of different breeds and training levels performed a 5 min warm-up program three times, with a 2 min break between the programs for recording purposes. Acoustic myography sensors were attached on the skin over the muscles m. triceps brachii (TB) and m. gluteus superficialis (GS). Recordings of muscle activity were made, while the dogs trotted before warm-up and after each 5 min warm-up program. The dogs used TB more efficiently after 5 min (P<0.05), 10 min (P<0.05) and 15 min (P<0.001) of exercise compared to pre-warm-up values. No changes were found in the activity of GS. For well-trained dogs, TB recruited fewer muscle fibres after 10 and 15 min of warm-up compared to dogs that trained less than 1 h weekly (P<0.03). For dogs with more than 2 years of experience, GS had a lower firing frequency before and after 10 min warm-up compared to dogs with less experience. The results indicate that warm-up alters muscle activation by an increased muscular efficiency. Training level and experience have an influence on muscle function parameters.

Acute effects of dynamic stretching on neuromechanical properties: an interaction between stretching, contraction, and movement

PURPOSE

The present study aimed to investigate the acute effects of dynamic stretching on neurophysiological and mechanical properties of plantar flexor muscles and to test the hypothesis that dynamic stretching resulted from an interaction between stretching, movement, and contraction.

METHODS

The dynamic stretching conditioning activity (DS) was compared to static stretching (SS), passive cyclic stretching (PCS), isometric contractions (IC), static stretching followed by isometric contractions (SSIC), and control (CO) conditions. Stretching amplitude (DS, SS, PCS and SSIC), contraction intensity (DS, IC and SSIC) and duration (all 6 conditions) were matched. Thirteen volunteers were included. Passive torque, fascicle length, and stiffness were evaluated from a dynamometer and ultrasonography during passive dorsiflexion. Neuromuscular electrical stimulation was used to investigate contractile properties [peak twitch torque (PTT), and rate of torque development (RTD)] and muscle voluntary activation (%VA). Gastrocnemius lateralis electromyographic activity (GL EMG/Mwave) was obtained during maximal voluntary contraction. All of these parameters were measured immediately before and 10 s after each experimental condition.

RESULTS

Peak twitch torque, RTD, %VA, GL EMG/Mwave remained unaltered, while passive torque was significantly reduced after DS (- 8.14 ± 2.21%). SS decreased GL EMG/Mwave (- 7.83 ± 12.01%) and passive torque (- 2.16 ± 7.25%). PCS decreased PTT (- 3.40 ± 6.03%), RTD (- 2.96 ± 5.16%), and passive torque (- 2.16 ± 2.05%). IC decreased passive torque (- 7.72 ± 1.97%) and enhanced PTT (+ 5.77 ± 5.19%) and RTD (+ 7.36 ± 8.35%). However, SSIC attenuated PTT and RTD improvements as compared to IC.

CONCLUSION

These results suggested that dynamic stretching is multi-component and would result from an interaction between stretching, contraction, and movement.

Thermotherapy Plus Neck Stabilization Exercise for Chronic Nonspecific Neck Pain in Elderly: A Single-Blinded Randomized Controlled Trial

Neck pain is a serious problem for public health. This study aimed to compare the effects of thermotherapy plus neck stabilization exercise versus neck stabilization exercise alone on pain, neck disability, muscle properties, and alignment of the neck and shoulder in the elderly with chronic nonspecific neck pain. This study is a single-blinded randomized controlled trial. Thirty-five individuals with chronic nonspecific neck pain were randomly allocated to intervention (n = 18) or control (n = 17) groups. The intervention group received thermotherapy with a salt-pack for 30 min and performed a neck stabilization exercise for 40 min twice a day for 5 days (10 sessions). The control group performed a neck stabilization exercise at the same time points. Pain intensity, pain pressure threshold (PPT), neck disability index, muscle properties, and alignment of the neck and shoulder were evaluated before and after the intervention. Significant time and group interactions were observed for pain at rest (p < 0.001) and during movement (p < 0.001), and for PPT at the upper-trapezius (p < 0.001), levator-scapula (p = 0.003), and splenius-capitis (p = 0.001). The disability caused by neck pain also significantly changed between groups over time (p = 0.005). In comparison with the control group, the intervention group showed significant improvements in muscle properties for the upper-trapezius (tone, p = 0.021; stiffness, p = 0.017), levator-scapula (stiffness, p = 0.025; elasticity, p = 0.035), and splenius-capitis (stiffness, p = 0.012), and alignment of the neck (p = 0.016) and shoulder (p < 0.001) over time. These results recommend the clinical use of salt pack thermotherapy in addition to neck stabilization exercise as a complementary intervention for chronic nonspecific neck pain control.

Changes in the Viscoelastic Properties of the Vastus Lateralis Muscle With Fatigue

We investigated the in vivo effects of voluntary fatiguing isometric contractions of the knee extensor muscles on the viscoelastic properties of the vastus lateralis (VL). Twelve young males (29.0 ± 4.5 years) performed an intermittent voluntary fatigue protocol consisting of 6 sets × 10 repetitions of 5-s voluntary maximal isometric contractions with 5-s passive recovery periods between repetitions. Voluntary and evoked torque were assessed before, immediately after, and 20 min after exercise. The shear modulus (μ) of the VL muscle was estimated at rest and during a ramped isometric contraction using a conventional elastography technique. An index of active muscle stiffness was then calculated (slope from the relationship between shear modulus and absolute torque). Resting muscle viscosity (η) was quantified using a shear-wave spectroscopy sequence to measure the shear-wave dispersion. Voluntary and evoked torque decreased by ∼37% (P < 0.01) immediately after exercise. The resting VL μ was lower at the end of the fatigue protocol (-57.9 ± 5.4%, P < 0.001), whereas the resting VL η increased (179.0 ± 123%, P < 0.01). The active muscle stiffness index also decreased with fatigue (P < 0.05). By 20 min post-fatigue, there were no significant differences from the pre-exercise values for VL η and the active muscle stiffness index, contrary to the resting VL μ. We show that the VL μ is greatly reduced and η greatly enhanced by fatigue, reflecting a more compliant and viscous muscle. The quantification of both shear μ and η moduli in vivo may contribute to a better understanding of the mechanical behavior of muscles during fatigue in sports medicine, as well as in clinical situations.

Effects of deep thermotherapy on chest wall mobility of healthy elderly women

Chest wall mobility decreases with age in community-dwelling women aged 65 years or older. Thermotherapy is used to improve soft-tissue extensibility. However, its effects on chest wall mobility are unclear. This study aimed to examine the effect of thermotherapy on chest wall mobility in healthy elderly women. Twenty-eight elderly women participated in this study. Chest wall mobility at three levels (axillary, xiphoid, and tenth rib), respiratory function (forced vital capacity and forced expiratory volume), and tissue temperature (skin temperature (ST)) and deep temperature (DT) with 10 mm and 20 mm depth from the skin (10 mm DT and 20 mm DT)) were measured before and after 15 minutes of thermotherapy. The subjects randomly received one of the three interventions (capacitive and resistive electric transfer (CRet), hot pack (HP), and sham CRet (sham)). Chest wall mobility at all levels significantly increased after CRet intervention. Hot pack significantly increased tenth rib excursion; it also significantly increased ST, 10 mm DT, and 20 mm DT, whereas CRet significantly increased 10 mm DT and 20 mm DT. There were significant differences between CRet, HP, and sham in ST, 10 mm DT, and 20 mm DT. Furthermore, 20 mm DT had increased more in CRet than in HP. CRet improved chest wall mobility at all levels and HP improved at the tenth rib level. This implies that CRet can be one of the approaches to improve chest wall mobility.

Effect of Capacitive and Resistive electric transfer on changes in muscle flexibility and lumbopelvic alignment after fatiguing exercise

[Purpose] This study aimed to clarify the effects of Capacitive and Resistive electric transfer (CRet) on changes in muscle flexibility and lumbopelvic alignment after fatiguing exercise. [Subjects and Methods] Twenty-two healthy males were assigned into either the CRet (n=11) or control (n=11) group. Fatiguing exercise and CRet intervention were applied at the quadriceps muscle of the participants' dominant legs. The Ely test, pelvic tilt, lumbar lordosis, and superficial temperature were measured before and after exercise and for 30 minutes after intervention. Statistical analysis was performed using one-way analysis of variance, with Tukey's post-hoc multiple comparison test to clarify within-group changes and Student's t-test to clarify between-group differences. [Results] The Ely test and pelvic tilt were significantly different in both groups after exercise, but there was no difference in the CRet group after intervention. Superficial temperature significantly increased in the CRet group for 30 minutes after intervention, in contrast to after the exercise and intervention in the control group. There was no significant between-group difference at any timepoint, except in superficial temperature. [Conclusion] CRet could effectively improve muscle flexibility and lumbopelvic alignment after fatiguing exercise.

Diurnal variation in repeated sprint performance cannot be offset when rectal and muscle temperatures are at optimal levels (38.5°C)

The present study investigated whether increasing morning rectal temperatures (T_rec) to evening levels, or increasing morning and evening T_rec to an "optimal" level (38.5°C), resulting in increased muscle temperatures (T_m), would offset diurnal variation in repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.0 ± 2.3 years, maximal oxygen consumption (V̇O₂max) 60.0 ± 4.4 mL.kg^-1 min^-1, height 1.79 ± 0.06 m, body mass 78.2 ± 11.8 kg]. These included control morning (M, 07:30 h) and evening (E, 17:30 h) sessions (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M_E, in 39-40°C water) until T_rec reached evening levels; two "optimal" trials in the morning and evening (M_38.5 and E_38.5, in 39-40°C water) respectively, until T_rec reached 38.5°C. All sessions included 3 × 3-s task-specific warm-up sprints, thereafter 10 × 3-s RS with 30-s recoveries were performed a non-motorised treadmill. T_rec and T_m measurements were taken at the start of the protocol and following the warm-up periods. Values for T_rec and T_m at rest were higher in the evening compared to morning values (0.48°C and 0.69°C, p < 0.0005). RS performance was lower (7.8-8.3%) in the M for distance covered (DC; p = 0.002), average power (AP; p = 0.029) and average velocity (AV; p = 0.002). Increasing T_rec in the morning to evening values or optimal values (38.5°C) did not increase RS performance to evening levels (p = 1.000). However, increasing T_rec in the evening to "optimal" level through a passive warm-up significantly reduced DC (p = 0.008), AP (p < 0.0005) and AV (p = 0.007) to values found in the M condition (6.0-6.9%). Diurnal variation in T_rec and T_m is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.

MR elastography measurement of the effect of passive warmup prior to eccentric exercise on thigh muscle mechanical properties

Purpose

To investigate the effect of warmup by application of the thermal agent Deep Heat (DH) on muscle mechanical properties using magnetic resonance elastography (MRE) at 3T before and after exercise‐induced muscle damage (EIMD).

Materials and Methods

Twenty male participants performed an individualized protocol designed to induce EIMD in the quadriceps. DH was applied to the thigh in 50% of the participants before exercise. MRE, T₂‐weighted MRI, maximal voluntary contraction (MVC), creatine kinase (CK) concentration, and muscle soreness were measured before and after the protocol to assess EIMD effects. Five participants were excluded: four having not experienced EIMD and one due to incidental findings.

Results

Total workload performed during the EIMD protocol was greater in the DH group than the control group (P < 0.03), despite no significant differences in baseline MVC (P = 0.23). Shear stiffness |G*| increased in the rectus femoris (RF) muscle in both groups (P < 0.03); however, DH was not a significant between‐group factor (P =  0.15). MVC values returned to baseline faster in the DH group (5 days) than the control group (7 days). Participants who displayed hyperintensity on T₂‐weighted images had a greater stiffness increase following damage than those without: RF; 0.61 kPa vs. 0.15 kPa, P < 0.006, vastus intermedius; 0.34 kPa vs. 0.03 kPa, P = 0.06.

Conclusion

EIMD produces increased muscle stiffness as measured by MRE, with the change in |G*| significantly increased when T₂ hyperintensity was present. DH did not affect CK concentration or soreness; however, DH participants produced greater workload during the EIMD protocol and exhibited accelerated MVC recovery.

Level of Evidence: 1

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2017;46:1115–1127.

Heat stress does not exacerbate tennis-induced alterations in physical performance

Objectives

To assess the time course of changes in physical performance in response to match-play tennis under heat stress.

Methods

Two matches consisting of 20 min of effective playing time (2×10 min segments) were played in COOL (∼102 min; ∼22°C and 70% relative humidity (RH)) and HOT (∼119 min; ∼36°C and 35% RH) environments. Repeated-sprint ability (3×15 m, 15 s rest), 15 m sprint time with a direction change (180°), vertical jump height (squat and countermovement jumps) and leg stiffness (multirebound jumps) were assessed in 12 competitive male players prematch, midmatch and postmatch, and 24 and 48 h after match completion.

Results

During the repeated-sprint ability test, initial (+2.3% and +3.1%) and cumulated sprint (+1.5% and +2.8%) times increased from prematch to midmatch and postmatch, respectively (p<0.001), while the sprint decrement score did not change. Match-play tennis induced a slowing (average of both conditions: +1.1% and +1.3% at midmatch and postmatch time points; p=0.05) of 15 m sprint time with direction change. Compared with prematch, leg stiffness (−6.4% and −6.5%; p<0.001) and squat jump height (−1.5% and −2.4%; p=0.05), but not countermovement jump height (−0.7% and −1.3%; p>0.05), decreased midmatch and postmatch, respectively, regardless of the condition. Complete recovery in all physical performance markers occurred within 24 h.

Conclusions

In tennis, match-related fatigue is characterised by impaired repeated-sprint ability, explosive power and leg stiffness at midmatch and postmatch, with values restored to prematch baseline 24 h into recovery. In addition, physical performance responses (match and recovery kinetics) are identical when competing in cool and hot environments.

Naturopathic reflex therapies for the treatment of chronic pain - Part 2: Quantitative sensory testing as a translational tool

Naturopathic reflex therapies such as massage, Gua Sha massage, cupping, wet packs etc. are likely able to influence chronic pain at different levels of the nociceptive system. Since naturopathic reflex therapies have been shown to reduce symptoms of chronic pain and often utilize intense manipulation of the environment of the nociceptor (e.g. Gua Sha massage or cupping), it can be hypothesized that they unfold part of their effect at the level of the peripheral nociceptor and the spinal cord. However, these hypotheses have to date not been tested systematically. Standardized sensory testing, e.g., as performed by 'quantitative sensory testing' (QST), a comprehensive battery of tests for clinical trials, may offer additional information about the mechanisms of naturopathic reflex therapies since it provides a measure for the mechanisms of nociceptive pain on all levels of the pain processing system. This method paper describes the potential role of QST in research on the neurobiological mechanisms of naturopathic reflex therapies.

Does raising morning rectal temperature to evening levels offset the diurnal variation in muscle force production?

Muscle force production and power output in active males, regardless of the site of measurement (hand, leg, or back), are higher in the evening than in the morning. This diurnal variation is attributed to motivational, peripheral and central factors, and higher core and, possibly, muscle temperatures in the evening. This study investigated whether increasing morning rectal temperatures to evening resting values, by active or passive warm-ups, leads to muscle force production and power output becoming equal to evening values in motivated subjects. Ten healthy active males (mean ± SD: age, 21.2 ± 1.9 yrs; body mass, 75.4 ± 8 kg; height, 1.76 ± .06 m) completed the study, which was approved by the University Ethics Committee. The subjects were familiarized with the techniques and protocol and then completed four sessions (separated by at least 48 h): control morning (07:30 h) and evening (17:30 h) sessions (with an active 5-min warm-up) and then two further sessions at 07:30 h but proceeded by an extended active or passive warm-up to raise rectal temperature to evening values. These last two sessions were counterbalanced in order of administration. During each trial, three measures of handgrip strength, isokinetic leg strength measurements (of knee flexion and extension at 1.05 and 4.19 rad.s(-1) through a 90° range of motion), and four measures of maximal voluntary contraction (MVC) on an isometric ergometer (utilizing the twitch-interpolation technique) were performed. Rectal and intra-aural temperatures, ratings of perceived exertion (RPE) and thermal comfort (TC) were measured. Measurements were made after the subjects had reclined for 30 min and after the warm-ups and prior to the measurement of handgrip and isokinetic and isometric ergometry. Muscle temperature was taken after the warm-up and immediately before the isokinetic and MVC measurements. Warm-ups were either active (cycle ergometer at 150 W) or passive (resting in a room at 35 °C, relative humidity 45%). Data were analyzed using analysis of variance models with repeated measures. Rectal and intra-aural temperatures were higher at rest in the evening (.56 °C and .74 °C; p < .05) than in the morning, but there were no differences after the active or passive warm-ups, the subjects' ratings of thermal comfort reflecting this. Muscle temperatures also displayed significant diurnal variation, with higher values in the evening (~.31 °C; p < .05). Grip strength, isokinetic knee flexion for peak torque and peak power at 1.05 rad.s(-1), and knee extension for peak torque at 4.19 rad.s(-1) all showed higher values in the evening. All other measures of strength or power showed a trend to be higher in the evening ( .10 > p > .05). There was no significant effect of active or passive warm-ups on any strength or power variable, and subjects reported maximal values for effort for each strength measure. In summary, effects of time of day were seen in some measures of muscle performance but, in this population of motivated subjects, there was no evidence that increasing morning rectal temperature to evening values by active or passive warm-up increased muscle strength to evening values.

Lack of effect of moderate-duration static stretching on plantar flexor force production and series compliance

BACKGROUND

The effects of an acute bout of moderate-duration static stretching on plantar flexor force production, series compliance of the muscle-tendon unit, and levels of neuromuscular activation were examined.

METHODS

Eighteen active individuals (9 men and 9 women) performed four 45-s static plantar flexor stretches and a time-matched control of no stretch (where subjects remained seated in the dynamometer for 4 min with no stretch being performed). Measures of peak isometric moment, rate of force development, neuromuscular activation (interpolated twitch technique and electromyography), twitch force characteristics, passive moment during stretch, and tendon elongation during maximal voluntary contractions were taken before and after the stretching.

FINDINGS

Despite a significant stress-relaxation response during stretch (9.3%, P<0.01) there were no significant differences in peak isometric moment (P=0.35; effect size 0.13), rate of force development (P=0.93; effect size 0.01), neuromuscular activation (interpolated twitch: P=0.86; electromyography: P=0.09; effect size 0.02), or tendon elongation (P=0.61; effect size 0.07) after stretching. Twitch characteristics were also unchanged after stretching, although there was a reduction in the rate of twitch torque relaxation (RR(t); P<0.01).

INTERPRETATION

The acute bout of moderate-duration static stretching did not impair the force generating capacity of the plantar flexors or negatively affect muscle-tendon mechanical properties. Static stretching may not always have detrimental consequences for force production. Thus, clinicians may be able to apply moderate-duration stretches to patients without risk of reducing muscular performance.

Whole-body vibration influences lower extremity circulatory and neurological function

Whole-body vibration (WBV) is currently used to enhance performance and treat injuries even though we lack an understanding of how WBV influences physiological processes. An improved understanding of the physiological effects of WBV could lead to protocols to speed healing or treat pathologies. This study examined the acute effects of WBV on peripheral blood perfusion, muscle oxygenation, motoneuron pool excitability, and sensory nerve conduction velocity. Fourteen healthy participants [9 women (21.7 ± 2.4 years); 5 men (20.8 ± 1.1 years)] completed a 5 min bout of WBV (50 Hz, 2 mm amplitude). Measures were assessed pre-treatment and at 0, 5, 10, 15, and 20 min post-treatment. WBV significantly increased superficial skin temperature (P < 0.0005) and total hemoglobin (P = 0.009), had no effect of oxyhemoglobin (P = 0.186), increased deoxyhemoglobin (P < 0.0005), inhibited the soleus Hoffmann reflex (P = 0.007), and had no effect on sural sensory nerve conduction velocity (P = 0.695). These results suggest that an acute bout of WBV influences physiological processes in both the circulatory and the nervous systems.

The relationship between massage to the equine caudal hindlimb muscles and hindlimb protraction

REASONS FOR PERFORMING STUDY

Massage is widely used in physiotherapy, but there has been little previous research examining its effectiveness in increasing equine soft tissue length.

OBJECTIVES

To determine the effect of massage on equine hindlimb protraction. We hypothesised that massage to the caudal muscles of the equine hindlimb, specifically the superficial gluteal, semitendinosus, biceps femoris and semimembranosus muscles, can increase passive and active hindlimb protraction.

MATERIALS AND METHODS

The study used a crossover design in which 8 horses were randomly assigned to 2 groups of 4, A and B. Group A received massage for 30 min, group B received sham treatment for 30 min. The procedure was repeated following a 7 day 'washout' period, when group A received the 30 min sham treatment and group B, 30 min of massage. Passive hindlimb protraction was measured before and after each intervention, using a modified version of the human 'Sit and Reach test' for general muscle flexibility. Active protraction was measured using 2 dimensional kinematic analysis of stride length. The data analysis used the Wilcoxon signed rank test at a significance of P < 0.05.

RESULTS

Massage to the caudal limb muscles significantly increased passive (P = 0.01) and active limb (P = 0.01) protraction.

CONCLUSIONS

This study indicates that massage can increase protraction of the equine hindlimb. Massage may, therefore, play a valuable role in the development of strategies used to improve a horse's locomotor function, e.g. during rehabilitation or optimum performance for competition.

Influence of stretching and warm-up on Achilles tendon material properties

BACKGROUND

Controversy exists on stretching and warm-up in injury prevention. We hypothesized that warm up has a greater effect on Achilles tendon biomechanics than static stretching. This study investigated static stretching and warm-up on Achilles tendon biomechanics in recreational athletes, in vivo.

MATERIALS AND METHODS

Ten active, healthy subjects, 5 males, 5 females, With a mean age of 22.9 years with no previous Achilles tendon injuries were recruited. Typical stretching and warm-up routines were created. Testing was performed in a randomized cross-over design. A custom-built dynamometer was utilized to perform controlled isometric plantarflexion. A low profile ultrasound probe was utilized to visualize the musculotendinous junction of the medial gastrocnemius. An eight-camera motion capture system was used to capture ankle motion. Custom software calculated Achilles tendon biomechanics.

RESULTS

Achilles tendon force production was consistent. No statistically significant differences were detected in stretch, stiffness, and strain between pre-, post-stretching, and post-warm-up interventions.

CONCLUSION

Stretching or warm-up alone, and combined did not demonstrate statistically significant differences. Stretching and warm-up may have an equivalent effect on Achilles tendon biomechanics. Prolonged and more intense protocols may be required for changes to occur.

CLINICAL RELEVANCE

Stretching and warm-up of the Achilles before exercise are commonly practiced. Investigating the effect of stretching and warm-up may shed light on potential injury prevention.

Princípios fisiológicos do aquecimento e alongamento muscular na atividade esportiva

O objetivo deste estudo foi revisar a importância do aquecimento e alongamento muscular na prática esportiva, destacando seus principais efeitos fisiológicos e benefícios, haja vista que o presente assunto tem causado muita dúvida aos atletas profissionais ou amadores bem como em profissionais da área da saúde na realização e prescrição, respectivamente, da prática do aquecimento e alongamento muscular. Foram utilizados 52 textos, entre artigos da base de dados PubMed e livros publicados de 1978 a 2008. Do total, 18 (34,62%) estavam em português e 34 (65,38%) em inglês. Resultados mostraram que o aquecimento tem por principal objetivo prevenir lesões devido à sua gama de efeitos fisiológicos. A realização do alongamento no término do gesto esportivo tem por finalidade evitar o encurtamento muscular, ou se realizado diariamente e por um longo período, favorecer o aumento do número de sarcômeros e, consequentemente, proporcionar um ganho de flexibilidade.

The relationship between passive ankle plantar flexion joint torque and gastrocnemius muscle and achilles tendon stiffness: implications for flexibility

STUDY DESIGN

Experimental laboratory study.

OBJECTIVES

We tested the hypothesis that the muscle fibers and the connective tendinous structures, combined in series, provide the resistance to passive joint movement at the ankle. We also determined the relative association between passive joint torque and each of these 2 elements.

BACKGROUND

The reason for individual variation in joint flexibility or tightness is not clearly understood, but the influence of musculotendinous stiffness has been inferred.

METHODS AND MEASURES

Each of the subjects (6 women and 6 men) was seated with the right knee extended and right ankle positioned at a 30 degrees , 20 degrees , 10 degrees , 0 degrees , -10 degrees , -20 degrees , and -30 degrees (0, neutral position, positive values reflecting plantar flexion) angle while passive plantar flexion torque was measured. The distal muscle-tendon junction of the medial gastrocnemius was visualized by ultrasonography, and its positional change was defined as muscle belly length change. The whole muscle-tendon unit length change was estimated from joint angle changes, from which Achilles tendon length change was estimated.

RESULTS

Both the muscle belly and tendon were significantly elongated as the ankle was dorsiflexed (at 0 degrees the mean +/- SD muscle belly elongation was 10.3% +/- 1.8 %, and the tendon elongation was 2.8% +/- 1.2 %, of the initial length at 30 degrees of ankle plantar flexion), from which stiffness indices were determined both for muscle belly and tendon. The passive torque at 0 degrees , -10 degrees , -20 degrees , and -30 degrees was significantly correlated with the stiffness indices of the Achilles tendon (at 0 degrees , r2 = 0.70 and 0.62 for overall and specific stiffness, respectively; P<.05). A tendon stiffness index, separately obtained from tendon lengthening during maximal isometric contraction, was also correlated with passive ankle plantar flexion torque at 0 degrees , -10 degrees , -20 degrees , and -30 degrees (at 0 degrees , r2 = 0.76; P<.05). The specific stiffness index of the muscle belly was correlated (r2 = 0.47, P<.05) with the passive ankle plantar flexion torque at 0 degrees , but its overall stiffness index was not (r2 = 0.32, P>.05).

CONCLUSION

Results suggest that extensibility of the muscle-tendon unit of the Achilles tendon for the most part is related to passive ankle plantar flexion joint torque.

The management of hamstring injury—Part 1: Issues in diagnosis

Hamstring injuries are the most prevalent muscle injury in sports involving rapid acceleration and maximum speed running. Injury typically occurs in an acute manner through an eccentric mechanism at the terminal stages of the swing phase of gait. Biceps femoris is most commonly injured. Re-injury rates are high and management is a challenge given the complex multi-factorial aetiology. The high rates of hamstring injury and re-injury may result from a lack of high-quality research into the aetiological factors underlying injury. Re-injury may also result from inaccuracy in diagnosis that results from the potential multi-factorial causes of these conditions. Inaccuracy in diagnosis could lead to multiple potential diagnoses that may result in the implementation of variable management protocols. Whilst potentially useful, such variability may also lead to the implementation of sub-optimal management strategies. Previous hamstring injury is the most recognized risk factor for injury, which indicates that future research should be directed at preventative measures. Much anecdotal and indirect evidence exists to suggest that several non-local factors contribute to injury, which may be addressed through the application of manual therapy. However, this connection has been neglected in previous research and literature. This paper will explore and speculate on this potential connection and offer some new contributive factors for hamstring injury management. This first paper of a two part series on hamstring injury will explore diagnostic issues relevant to hamstring injury and the second will investigate various established and speculative management approaches.

Paraspinal musculature and skin temperature changes: comparing the Thermacare HeatWrap, the Johnson & Johnson Back Plaster, and the ABC Warme-Pflaster

STUDY DESIGN

Prospective, randomized, crossover design.

OBJECTIVES

To compare the effectiveness of the Johnson & Johnson Back Plaster, the ABC Warme-Pflaster, and the ThermaCare HeatWrap on skin and paraspinal muscle temperature. Also, to compare the subjects' heat perception for the 3 products.

BACKGROUND

Heat therapy is a common treatment for low back pain and disability. There are a number of products on the market that are suggested to relieve low back pain by providing warmth to the back; however, their effectiveness for increasing tissue temperature compared with heat sensation has not been tested.

METHODS AND MEASURES

To measure paraspinal muscle temperature, 1 thermocouple monofilament was inserted into the paraspinal muscle 2 cm from the skin surface at the L3 level using a 20-gauge 1.25-in (3.15-cm) sterile catheter. To measure skin interface temperature, 2 thermocouples were placed on the skin at distances of 5 cm and 7 cm from the insertion site. The Isothermex was used to record temperatures to the nearest 0.1 degrees C for 120 minutes. The subjects also rated heat perception using a 10-cm visual analog scale at 0, 30, 60, 90, and 120 minutes. Analysis of covariance models were used for statistical analysis.

RESULTS

There was a significant product x time interaction (F14,231 = 3.77, P<.0001) at the intramuscular site, but there was not a significant product x time interaction (F14,231 = 1.03, P = .4228) at the skin site. Both the main effects for product (F2,33 = 41.59, P<.0001) and time (F3,51 = 19.02, P<.0001) were significant for the visual analog scale data. The ThermaCare HeatWrap produced significant increases in both skin and intramuscular temperatures with less heat sensation. The Johnson & Johnson Back Plaster and the ABC Warme-Pflaster increased temperature at the skin surface and provided the greatest heat sensations, but they did not provide intramuscular heat.

CONCLUSIONS

The ThermaCare HeatWrap is more effective at increasing temperature at a 2-cm depth with less perceived heat compared to the Johnson & Johnson Back Plaster and the ABC Warme-Pflaster. The latter 2 products provide a sensation of heat but do not actually provide a muscle temperature change at a depth of 2 cm.

Effect of heat modalities on hamstring length: a comparison of pneumatherm, moist heat pack, and a control

STUDY DESIGN

Prospective, researcher-blinded, repeated-measures, randomized complete block design.

OBJECTIVES

To compare the effects of a single treatment of Pneumatherm, moist heat pack, and a control treatment on hamstring muscle length.

BACKGROUND

Traditionally, heating modalities have been used to facilitate increases in tissue length. The Pneumatherm has been developed over the past 20 years for use in the clinical treatment of a variety of musculoskeletal pathologies. However, there is no published evidence supporting the use of Pneumatherm for improving muscle length.

SUBJECTS

Participants consisted of 30 healthy, college-age males taken from a convenience sampling from the University of Indianapolis student population.

METHODS AND MEASURES

Participants received a 3-treatment sequence on consecutive days. Treatments involved applying the determined modality to the posterior thigh using standard treatment protocols. A hand-held dynamometer was used to establish a consistent passive measurement force to measure hamstring muscle length.

RESULTS

A mixed-model analysis of variance with pretest-posttest (3 pretest and 3 posttest measures) and treatment sequence of the modalities (6 sequences of Pneumatherm, moist heat, and control) was completed. The only significant effect was for pretest-posttest measures. Post hoc comparisons revealed that the Pneumatherm posttest value was significantly different from all other measures. There were no differences found between pretest scores and the moist heat and control posttest scores.

CONCLUSIONS

Our results demonstrate that the Pneumatherm modality is an effective agent for increasing hamstring muscle length following a single 20-minute treatment. In this study, a significant gain in hamstring muscle length was not found following a 1-time treatment with moist heat. The Pneumatherm may be a good option when heat is used to assist in gaining flexibility of the hamstring musculature.

The efficacy of stretching for prevention of exercise-related injury: a systematic review of the literature

The objective of this study was to conduct a systematic analysis of the literature to assess the efficacy of stretching for prevention of exercise-related injury. Randomized clinical trials (RCTs) and controlled clinical trials (CCTs) investigating stretching as an injury prevention measure were selected. A computer-aided search of the literature was conducted for relevant articles, followed by assessment of the methods of the studies. The main outcome measures were scores for methodological quality based on four main categories (study population, interventions, measurement of effect, and data presentation and analysis) and main conclusions of authors with regard to stretching. One RCT (25%) and three CCTs (100%) concluded that stretching reduced the incidence of exercise-related injury. Three RCTs (75%) concluded that stretching did not reduce the incidence of exercise-related injury. Only two studies scored more than 50 points (maximum score=100 points) indicating that most of the studies selected were of poor quality. Neither of the two highest scoring RCTs showed positive effects for stretching. Due to the paucity, heterogeneity and poor quality of the available studies no definitive conclusions can be drawn as to the value of stretching for reducing the risk of exercise-related injury.

Effects of warm-up before eccentric exercise on indirect markers of muscle damage

PURPOSE

To test whether active and passive warm-up conducted before eccentric exercise attenuates clinical markers of muscle damage.

METHODS

Untrained subjects were exposed to one of five conditions: low-heat passive warm-up (N = 10), high-heat passive warm-up (N = 4), or active warm-up (N = 9), preceding eccentric exercise; eccentric exercise without warm-up (N = 10); or high-heat passive warm-up without eccentric exercise (N = 10). Passive warm-up of the elbow flexors was achieved using pulsed short-wave diathermy, and active warm-up was achieved by concentric contraction. Creatine kinase (CK) activity, strength, range of motion, swelling, and muscle soreness were observed before treatment (baseline) and 24, 48, 72, and 168 h after treatment.

RESULTS

High-heat passive warm-up without eccentric exercise did not affect any marker of muscle damage and was used as our control group. Markers of muscle damage were not different between groups that did or did not conduct warm-up before eccentric exercise. The active warm-up and eccentric groups exhibited a greater circumferential increase than controls (P < 0.0002), however, that was not observed after passive warm-up. Additionally, the active warm-up group exhibited a greater CK response than controls at 72 h (P < 0.05). The high-heat passive warm-up before eccentric exercise group exhibited significant change from controls at the least number of time points, but due to a small sample size (N = 4), these data should be viewed as preliminary.

CONCLUSION

Our observations suggest that passive warm-up performed before eccentric exercise may be more beneficial than active warm-up or no warm-up in attenuating swelling but does not prevent, attenuate, or resolve more quickly the other clinical symptoms of eccentric muscle damage as produced in this study.

Effects of transient muscle contractions and stretching on the tendon structures in vivo

This study compared the effects of static stretching (ST) and repeated muscle contractions (CON) on the viscoelastic properties of tendon structures in vivo. Eight male subjects performed ST (passively flexed to 35 of dorsiflexion) for 5 min and 50 repetitions of isometric maximum voluntary contraction (MVC) for 3 s each with 3 s relaxation. Before and after each task, the elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured by ultrasonography, while the subjects performed ramp isometric plantar flexion up to MVC, followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) and tendon elongation (L) during the ascending phase was applied to a linear regression, the slope of which was defined as stiffness of the tendon structures. The percentage of the area within the Fm-L loop to the area beneath the curve during the ascending phase was calculated as an index representing hysteresis. The ST protocol significantly decreased the stiffness (-8%) and hysteresis (29%)., respectively. In contrast, the CON protocol significantly decreased the stiffness, but not the hysteresis. These results suggested that the stretching and repeated contractions would make the tendon structures more complaint, and further decreased the hysteresis of the tendon structures.

Muscle disorders and rehabilitation in canine athletes

Muscle disorders associated with physical exertion in human athletes include delayed-onset muscle soreness, muscle strain, muscle tears, rhabdomyolysis, and acute and chronic compartment syndromes. Given that the structure of muscle is similar among different species, it is reasonable to expect that dogs experience the same phenomena. This article focuses on several of the muscle disorders of bird dogs, namely, coccygeal muscle injury and infraspinatus muscle contracture, and on those of dogs involved in tracking-obedience-protection training, namely, fibrotic myopathy, with an additional discussion of muscle strain. For injury prevention, one important area that can be adapted to canine athletes is the incorporation of warm-up and cool-down into the training program.

Influences of repetitive muscle contractions with different modes on tendon elasticity in vivo

The present study aimed to investigate the effects of repetitive muscle contractions on the elasticity of human tendon structures in vivo. Before and after each endurance test, the elongation of the tendon and aponeurosis of vastus lateralis muscle (L) was directly measured by ultrasonography while the subjects performed ramp isometric knee extension up to maximal voluntary isometric contraction (MVC). Six male subjects performed muscle endurance tests that consisted of knee extension tasks with four different contraction modes: 1) 50 repetitions of maximal voluntary eccentric action for 3 s with 3 s of relaxation (ET1), 2) three sets of 50 repetitions of MVC for 1 s with 3 s of relaxation (ET2), 3) 50 repetitions of MVC for 3 s with 3 s of relaxation (ET3), and 4) 50 repetitions of 50% MVC for 6 s with 6 s of relaxation (ET4). In ET1 and ET2, there were no significant differences in L values at any force production levels between before and after endurance tests. In the cases of ET3 and ET4, however, the extent of elongation after the completion of the tests tended to be greater. The L values above 330 N in ET3 and 440 N in ET4, respectively, were significantly greater after endurance tests than before. These results suggested that the repeated longer duration contractions would make the tendon structures more compliant and that the changes in the elasticity might be not be affected by either muscle action mode or force production level but by the duration of action.

Intrinsic and extrinsic risk factors for muscle strains in Australian football

Muscle strains are common injuries in Australian football and other sports involving sprinting. Between 1992 and 1999, 83,503 player-matches in the Australian Football League were analyzed for risk of muscle strain injuries using logistic regression analysis. There were 672 hamstring, 163 quadriceps, and 140 calf muscle strain injuries. All three types of muscle strains were associated with significant risk factors. For all injuries, the strongest risk factor was a recent history of that same injury and the next strongest risk factor was a past history of the same injury. History of one type of muscle strain increased the risk for certain types of other muscle strains. Age was a risk factor for hamstring and calf muscle strains (even when adjusted for injury history) but was not a risk factor for quadriceps muscle strains. Quadriceps muscle injuries were more common in shorter players and were more likely when there had been less rainfall at the match venue in the previous week. Quadriceps muscle injuries were significantly more common in the dominant kicking leg, whereas hamstring and calf muscle injuries showed no difference in frequency between the dominant and nondominant legs.

Stretching at the ankle joint: viscoelastic responses to holds and continuous passive motion

PURPOSE

To compare the effect of static holds and continuous passive motion on stiffness and force relaxation of the soft tissue structures resisting ankle joint dorsiflexion.

METHODS

This study used a randomized repeated measures trial design. Twenty-four asymptomatic subjects (15 males and 8 females) with a mean age of 26 yr participated. A Kin-Com dynamometer was used to measure the stiffness and force relaxation response of tissues about the ankle joint in response to a plantar flexor stretch. A comparison was made of the response for a 1 x 60-s hold, 2 x 30-s holds, 4 x 15-s holds, and continuous passive motion for 60 s. All subjects undertook all conditions. The main outcome measures were 1) stiffness at the ankle joint as it moved to 80% of the maximum range of dorsiflexion, and 2) the decrease in force at 80% of the maximum range of motion of the ankle joint.

RESULTS

Stiffness was decreased significantly (P < 0.05) for the continuous passive motion condition only. The mean magnitude of the decrease in stiffness was 16%. Across hold times, force decreased significantly (P < 0.05). Bonferonni contrasts indicated that there was a significant difference (P < 0.05) between the continuous passive motion condition and all other hold conditions. There were no significant differences (P > 0.05) between the 4 x 15-s, 2 x 30-s, and 1 x 60-s holds. The magnitude of the decline in force was 10.5%, 21.5%, 21.7%, and 19% for the 0-, 15-, 30-, and 60-s holds, respectively. The greatest decreases in tension were achieved in the first 20 s of a hold.

CONCLUSION

If decreasing stiffness is a key aim of a stretching program, the findings indicate that continuous motion is more effective than holds. In contrast, if relaxation of peak tension is the main aim, then holds are most effective.

Passive energy return after repeated stretches of the hamstring muscle-tendon unit

It has been shown that five repetitive static stretches of human hamstring muscle, each lasting 90 s and separated by 30 s, altered the passive properties on a short-term basis. However, a total of 7.5 min (5 x 90 s) of stretching for a single muscle group may be an unrealistic stretching program.

PURPOSE

The present investigation examined whether three repeated 45-s static stretches had a measurable effect on the passive properties of the hamstring muscle-tendon unit, in vivo.

METHODS

Resistance to stretch was defined as the passive moment (Nm) offered by the hamstring muscle group during passive knee extension using a KinCom dynamometer as previously described (Kinetic Communicator, Chattecx Corp., Chattanooga, TN). The static stretch exercise was administered to the left lower extremity of all subjects and consisted of a dynamic phase of passive knee extension to a predetermined final joint angle followed by a 45-s static phase. The procedure was repeated for a total of three 45-s static stretches with 30-s rest period between stretches.

RESULTS

There was a significant decline in resistance over the 45-s the static phase in stretch 1 (20 +/- 3%) and stretch 3 (18 +/- 3%), P < 0.001. Further, the absolute or relative decline in resistance over time stretch 1 and 3 were equivalent. The mean resistance in stretch 1 and 3, expressed as the log(e) of time, yielded an equal and highly linear relationship (r2 = 0.96 +/- 0.01); the slope and intercept did not differ. In the dynamic phase of the stretch, the energy of stretch 1 and 3 were similar.

CONCLUSIONS

These data suggest that the static stretching protocol used in the present study had no short-term effect on the viscoelastic properties of human hamstring muscle group.

Passive energy absorption by human muscle-tendon unit is unaffected by increase in intramuscular temperature

The present study measured hamstring intramuscular temperature and muscle-tendon unit viscoelastic properties in healthy young men before and after 10 and 30 min of running with (day S) or without stretch (day NS). On day NS, passive energy absorption and intramuscular temperature were measured before running (Preex), after 10 min of running at 70% of maximum O(2) uptake (Postex10), and after 30 min of running at 75% of maximum O(2) uptake (Postex30). On day S, the protocol was repeated with three stretches (stretches 1-3) added after Postex10. Intramuscular temperature was elevated Postex10 (P < 0.01) and further Postex30 (P < 0.05). On day NS, the total energy absorbed Preex (14.3 +/- 2.3 J), Postex10 (14.5 +/- 3.2 J), and Postex30 (13.5 +/- 2.4 J) was not different. On day S, the total energy absorbed in stretch 3 (10.8 +/- 1.8 J) was lower than that Preex (14.5 +/- 1.7 J, P < 0.01) and Postex10 (13.5 +/- 1.9 J, P < 0.05) but not Postex30 (13.3 +/- 1.8 J). The total energy absorbed Postex30 did not differ from Preex. In conclusion, warm-up and continuous running elevated intramuscular temperature but did not affect the passive energy absorption. Repeated passive stretching reduced the energy absorption immediately; however, the effect did not remain after 30 min of running. These data suggest that passive energy absorption of the human skeletal muscle is insensitive to physiological increases in intramuscular temperature.

Repeated passive stretching: acute effect on the passive muscle moment and extensibility of short hamstrings

OBJECTIVE

To examine the response of short hamstring muscles to repeated passive stretching.

DESIGN

A repeated measures design.

SETTING

A university laboratory for human movement analysis in a department of rehabilitation.

SUBJECTS

Students (7 men, 10 women) from the Department of Human Movement Sciences.

MAIN OUTCOME MEASURES

The lift force, range of motion, pelvic-femoral angle, first sensation of pain, and electromyogram of the hamstrings were measured.

RESULTS

Comparison of the data of the test group (n = 17) after five successive passive stretch tests by means of an instrumental straight-leg raising test showed no significant change of the variables passive muscle stiffness and extensibility (p>.05).

CONCLUSION

The acute effect of repeated passive stretching of short hamstring muscles is negligible. With an instrumental straight-leg raising test, the relevant muscle variables can be examined noninvasively.

Passive properties of human skeletal muscle during stretch maneuvers. A review

Despite limited scientific knowledge, stretching of human skeletal muscle to improve flexibility is a widespread practice among athletes. This article reviews recent findings regarding passive properties of the hamstring muscle group during stretch based on a model that was developed which could synchronously and continuously measure passive hamstring resistance and electromyographic activity, while the velocity and angle of stretch was controlled. Resistance to stretch was defined as passive torque (Nm) offered by the hamstring muscle group during passive knee extension using an isokinetic dynamometer with a modified thigh pad. To simulate a clinical static stretch, the knee was passively extended to a pre-determined final position (0.0875 rad/s, dynamic phase) where it remained stationary for 90 s (static phase). Alternatively, the knee was extended to the point of discomfort (stretch tolerance). From the torque-angle curve of the dynamic phase of the static stretch, and in the stretch tolerance protocol, passive energy and stiffness were calculated. Torque decline in the static phase was considered to represent viscoelastic stress relaxation. Using the model, studies were conducted which demonstrated that a single static stretch resulted in a 30% viscoelastic stress relaxation. With repeated stretches muscle stiffness declined, but returned to baseline values within 1 h. Long-term stretching (3 weeks) increased joint range of motion as a result of a change in stretch tolerance rather than in the passive properties. Strength training resulted in increased muscle stiffness, which was unaffected by daily stretching. The effectiveness of different stretching techniques was attributed to a change in stretch tolerance rather than passive properties. Inflexible and older subjects have increased muscle stiffness, but a lower stretch tolerance compared to subjects with normal flexibility and younger subjects, respectively. Although far from all questions regarding the passive properties of humans skeletal muscle have been answered in these studies, the measurement technique permitted some initial important examinations of vicoelastic behavior of human skeletal muscle.

Viscoelastic behavior of plantar flexor muscle-tendon unit at rest

Muscle stretching as an exercise routine is widely used in orthopaedic and neurological rehabilitation. However, the muscle response to specific stretching parameters is still unclear. The aim of this study was to investigate the effect parameters, such as stretch velocity, stretch extent, and initial muscle-tendon resistance, on the plantar flexor response to passive movement. Eighteen healthy subjects (23-41 years) participated in this study. Five passive ankle dorsiflexions were randomly imposed at various velocities from 5 degrees/sec to 180 degrees/sec using a Kin-Com dynamometer, while unwanted activations of the soleus and tibialis anterior muscles were detected with surface electrodes. The resistive torque was averaged at -10 degrees and 0 degree of dorsiflexion. As shown by analyses of variance followed by Scheffé post hoc procedures, the resistive torque was significantly increased (p < 0.01) between 5 degrees/sec and higher velocities (60 degrees/sec or 120 degrees/sec and higher). A strong linear resistive torque-velocity relationship was also observed, as indicated by Pearson correlation coefficients of 0.92 (-10 degrees) and 0.91 (0 degree). The absolute resistive torque increment, calculated at 180 degrees/sec, was larger at 0 degree of dorsiflexion than at the -10 degrees of dorsiflexion position. Finally, subjects with larger initial plantar flexor resistance had a higher resistive torque increment (p < 0.05) at a high velocity of stretch (180 degrees/sec) than those with less initial muscle-tendon resistance. These results indicate that 1) the nonreflex resistive torque response to stretch is velocity-sensitive and 2) both a larger stretch extent and muscle initial resistance lead to greater resistive torque increments at high velocity. These observations suggest that slow and gradual stretching procedures, rather than rapid or ballistic movements, should be used, especially with stiff muscles to reduce the chance of injury from excessively high tension.

Flexibility and its effects on sports injury and performance

Flexibility measures can be static [end of ROM (range of motion)], dynamic-passive (stiffness/compliance) or dynamic-active (muscle contracted, stiffness/compliance). Dynamic measures of flexibility are less dependent on patient discomfort and are more objective. Acute and chronic changes in flexibility are likely to occur with stretching exercises, but it is difficult to distinguish between changes in stretch tolerance as opposed to changes in muscle stiffness. How flexibility is measured impacts these findings. There is no scientifically based prescription for flexibility training and no conclusive statements can be made about the relationship of flexibility to athletic injury. The literature reports opposing findings from different samples, frequently does not distinguish between strain, sprain and overuse injury, and rarely uses the proper denominator of exposure. There is basic scientific evidence to suggest that active warm-up may be protective against muscle strain injury but clinical research is equivocal on this point. Typically, specific flexibility patterns are associated with specific sports and even positions within sports. The relationship of flexibility to athletic performance is likely to be sport-dependent. Decreased flexibility has been associated with increased in-line running and walking economy. Increased stiffness may be associated with increased isometric and concentric force generation, and muscle energy storage may be best manifested by closely matching muscle stiffness to the frequency of movement in stretch-shorten type contractions.

A mechanism for altered flexibility in human skeletal muscle

1. We investigated the effect of a long-term stretching regimen on the tissue properties and stretch tolerance of human skeletal muscle. 2. Resistance to stretch was measured as torque (in N m) offered by the hamstring muscle group during passive knee extension while electromyographic (EMG) activity, knee joint angle and velocity were continuously monitored during a standardized stretch manoeuvre. Seven healthy subjects were tested before and after a 3 week training period using two separate protocols. Protocol 1 consisted of a slow stretch at 0.087 rad s-1 to a predetermined angle followed by a 90 s holding phase. Subjects were brought to the same angle before and after the training period. Protocol 2 was a similar stretch, but continued to the point of pain. 3. During protocol 1 the torque rose during the stretch and then declined during the holding phase. EMG activity was small and did not change significantly during the protocol. No significant differences in stiffness, energy and peak torque about the knee joint were seen as a result of the training. During protocol 2 the angle to which the knee could be extended was significantly increased as a result of the training. This was accompanied by a comparable increase in peak torque and energy. EMG activity was small and not affected by training. 4. It is concluded that reflex EMG activity does not limit the range of movement during slow stretches and that the increased range of motion achieved from training is a consequence of increased stretch tolerance on the part of the subject rather than a change in the mechanical or viscoelastic properties of the muscle.

Biomechanical responses to repeated stretches in human hamstring muscle in vivo

To examine stiffness, energy, and passive torque in the dynamic and static phases of a stretch maneuver in the human hamstring muscle in vivo we used a test-retest protocol and a repeated stretches protocol. Resistance to stretch was defined as passive torque (in newton-meters) offered by the hamstring muscle group during passive knee extension as measured using an isokinetic dynamometer with a modified thigh pad. In 13 uninjured subjects, the knee was passively extended to a predetermined final position (0.0875 rad/ sec, dynamic phase) where it remained stationary for 90 seconds (static phase). The test-retest protocol included two tests administered 1 hour apart. On a separate occasion, five consecutive static stretches were administered separated by 30 seconds and followed by a sixth stretch 1 hour later. For the test-retest phase, stiffness and energy in the dynamic phase and passive torque in the static phase did not differ and yielded correlations of r = 0.91 to 0.99. During the static phase, passive torque declined in both tests (P < 0.0001). For the repeated stretches, decreases were observed for energy (P < 0.01) and stiffness (P < 0.05) in the dynamic phase and for passive torque (P < 0.0001) in the static phase. However, the decline in the variables returned to baseline within 1 hour. The data show that the method employed is a useful tool for measuring biomechanical variables during a stretch maneuver. This may provide a more detailed method to examine skeletal muscle flexibility.

Mechanical and physical responses to stretching with and without preisometric contraction in human skeletal muscle

OBJECTIVE

To examine electromyography (EMG) activity, passive torque, and stretch perception during static stretch and contract-relax stretch.

DESIGN

Two separate randomized crossover protocols: (1) a constant angle protocol on the right side, and (2) a variable angle protocol on the left side.

SUBJECTS

10 male volunteers.

INTERVENTION

Stretch-induced mechanical response in the hamstring muscles during passive knee extension was measured as knee flexion torque (Nm) while hamstring surface EMG was measured. Final position was determined by extending the knee to an angle that provoked a sensation similar to a stretch maneuver. Constant angle stretch: The knee was extended to 10 degree below final position, held 10sec, then extended to the final position and held for 80 sec. Variable angle stretch: The knee was extended from the starting position to 10 degrees below the final position, held 10sec, then extended to the onset of pain. Subjects produced a 6-sec isometric contraction with the hamstring muscles 10 degrees below the final position in the contract-relax stretch, but not in the static stretch.

MAIN OUTCOME MEASURES

Passive torque, joint range of motion, velocity, and hamstring EMG were continuously recorded.

RESULTS

Constant angle contract-relax and static stretch did not differ in passive torque or EMG response. In the final position, passive torque declined 18% to 21% in both contract-relax and static stretch (p<.001), while EMG activity was unchanged. In the variable angle protocol, maximal joint angle and corresponding passive torque were significantly greater in contract-relax compared with static stretch(p<.01), while EMG did not differ.

CONCLUSION

At a constant angle the viscoelastic and EMG response was unaffected by the isometric contraction. The variable angle protocol demonstrated that PNF stretching altered stretch perception.

Thermal pants may reduce the risk of recurrent hamstring injuries in rugby players

OBJECTIVE

To determine whether the use of thermal pants might reduce the risk of hamstring injury in rugby players.

METHODS

44 male rugby players from the Cape Province, South Africa, who had previously suffered a hamstring injury were given the choice of wearing thermal warming pants or not, and were then monitored for the development of hamstring injuries during the 1992 season.

RESULTS

In the group who wore warmers some of the time, the injury rate was significantly lower when using the warmers (3 injuries/1000 playing hours) than when not (57/1000 playing hours). There was no difference in injury rates between groups who either wore warmers all the time or none of the time, probably because the number who wore the warmers all the time was small (n = 5). Eighteen percent of the injuries recurred at exactly the same site in the muscle and within 12 d of returning to rugby after the initial injury. The incidence of injury was high in the first three weeks of the season and again in the same period after the mid-season break. More than 80% of all match and practice time lost by these players during the study was a direct result of their hamstring injuries.

CONCLUSIONS

Thermal pants may have a role in preventing recurrent hamstring injuries but other factors such as inadequate preseason training and incomplete rehabilitation after injury are likely to be more significant risk factors for injury.

Hamstring muscle injuries among water skiers. Functional outcome and prevention

Water skiing is associated with severe injuries to the proximal hamstring muscles. We wanted to define the mechanism of injury, describe the associated pathologic changes, determine the functional limitations of patients, and suggest measures to prevent injury. Twelve patients with water skiing-related hamstring injuries were included. Six patients were experienced skiers and six were novices. The mechanism of injury was identical in five of six novice skiers. Each sustained the injury while attempting to get up on one or two skis from a submerged position. In contrast, the expert skiers all sustained injury secondary to a fall while skiing. Physical examination documented evidence of complete or partial avulsion of the proximal hamstring muscle origins in all patients. In addition, six patients had magnetic resonance imaging or computed tomography scans that confirmed the location and extent of the tear. Convalescence ranged from 3 months to 1.5 years before the patient could return to vigorous activities. Seven patients (58%) returned to most of their preinjury sports, albeit at a lower level. Five patients (42%), all with complete disruptions, were unable to run or participate in sports requiring agility. Two of these patients required delayed surgical repairs because of persistent functional limitations.

The influence of stretching and warm-up exercises on Achilles tendon reflex activity

The aim of this study was to investigate the acute effects of prior exercise (warm-up and stretching) on the electromyographic and force output of mechanically elicited triceps surae reflexes. Fifty male subjects performed eight reflex experiments under each of three successive conditions in one session: (1) no prior exercise, (2) after static stretching of the passive triceps surae (3 min) and (3) after a 10-min warm-up run on a treadmill. Tendon tap reflex force was elicited in the triceps surae of the right leg by means of a standardized reflex hammer and measured in a custom-built fixture. Electromyographic (EMG) signals were recorded with surface electrodes over the medial head of the gastrocnemius (G) and the soleus (S). Low coefficients of variation within subjects contrasted with high between-subject variations, indicating highly individual reflex characteristics. After stretching, reductions in the peak force (-5%; P < 0.05), the force rise rate (-8%; P < 0.01), the half relaxation rate (-5%; N.S.), the EMG amplitudes (G, -16%; S, -17%; P < 0.01) and integrals (G, -15%; S, -18%; P < 0.01), and an increase in EMG latencies (G, +3%; S, +1%; P < 0.01), were found compared with the values obtained without prior exercise. After running, the peak force reached the values obtained without prior exercise (-2%; N.S.), the force rise rate and half relaxation rate increased by 8 and 12%, respectively (P < 0.01), and the impulse (force-time integral; -12%), EMG amplitudes (G, -20%; S, -23%; P < 0.01), integrals (G, -18%; S, -23%; P < 0.01) and latencies (G, -1%; S, -2%; P < 0.01) decreased significantly. The changes in the force characteristics observed after the stretching treatment indicate improved muscle compliance that might reduce the risk of injury. On the other hand, the changes after the additional warm-up run had a more pronounced influence with regard to improved force development and a decreased EMG activity, which can be viewed as a performance-enhancing effect.

Contraction specific changes in passive torque in human skeletal muscle

The present investigation examined passive torque and electromyographic response in human skeletal muscle during passive static stretch within 60 s after maximal repetitive eccentric and concentric contractions. Passive torque (Nm) offered by the hamstring muscle group was measured during passive knee extension in a modified dynamometer in 10 subjects. The distal thigh was elevated to 0.52 rad from horizontal and the backrest was positioned at 1.57 rad. The lever arm moved the leg passively at 0.09 rad s-1 from a starting position of 1.48 rad below horizontal to the final position where it remained stationary for 90 s. Gross electrical activity of the human hamstring muscle group was recorded simultaneously. The effect of concentric or eccentric contraction was tested on separate days. Two stretch manoeuvres with a 45 min hiatus were administered on a control and experimental side. The experimental side performed 40 maximal effort repetitive concentric or eccentric hamstring muscle contractions at 1.05 rad s-1 prior to the second stretch. Passive torque during the 90 s stretch declined 30-35% on the experimental and control side in all stretches, P < 0.001, without a significant effect of prior contraction mode. Passive peak and final torques were lower on the experimental side, P < 0.01 after concentric contractions. Passive peak and final torques remained unchanged after eccentric contractions on the experimental side. The low level EMG response of the hamstring muscle during the stretch was unchanged after maximal repetitive concentric or eccentric contractions. These data demonstrate acute contraction specific alteration in passive torque in human skeletal muscle, which cannot be accounted for by EMG activity. Furthermore, the lack of difference on the control side implies that one 90 s stretch has no effect on passive torque of the muscle 45 min later.