The role of passive muscle stiffness in symptoms of exercise-induced muscle damage

Impact of an acute bout of vibration on muscle contractile properties, creatine kinase and lactate dehydrogenase response

The aim of this study was to assess the effects of a bout of whole body vibration (WBV) on muscle response and to determine whether this stimulus leads to muscle damage. Thirty healthy and physically active participants (mean ± SD; age: 21.8 ± 2.0 years; height: 176.7 ± 5.8 cm; body mass: 76 ± 6.8 kg and BMI: 23.1 ± 3.7 kg·m(-2)) participated in this study. Participants were randomly allocated in one of two groups, one of them performed a bout of 360 s WBV (frequency: 30 Hz; peak-to-peak displacement: 4 mm) (VIB) and the other one adopted a sham position (CON). Muscle contractile properties were analysed in the rectus femoris (RF) by using tensiomyography (TMG) 2 min before the warm-up and 2 min after intervention. Muscle damage was assessed by determining plasma creatine kinase (CK) and lactate dehydrogenase (LDH) levels at three time points; 5 min before warm-up and 1 h and 48 h after the intervention. TMG results showed a significant decrease in maximal displacement (p<0.05) and delay time (p<0.05) in VIB and in delay time (p<0.05) and relaxation time (p<0.05) in CON. Muscle damage markers showed significant group differences (p<0.05) for CK 1 h after the intervention. In addition, differences for CK 1 h after the intervention from baseline (p<0.05) were also observed in VIB. In conclusion, a 6-min bout of WBV results in an increase of muscle stiffness in RF and increased CK levels 1 h after intervention (returning to baseline within 48 h).

Biomechanical properties of the plantar flexor muscle-tendon complex 6 months post-rupture of the Achilles tendon

We compared the effects of a non-weight bearing protocol (NWB) and a weight bearing (WB) protocol on energy stored, stiffness, and shock absorption in the plantar flexor muscle-tendon unit of patients managed non-operatively following an Achilles tendon rupture. Thirty-eight subjects were randomized to a WB cast fitted with a Bohler iron or a traditional non-weight-bearing cast. At a 6-month follow-up, a biomechanical assessment utilizing an isokinetic dynamometer allowed measurement of peak passive torque, energy stored, shock absorption, and stiffness. The WB group had greater peak passive torque (≈ 20%). Irrespective of group, peak passive torque in unaffected legs was greater (≈ 26%) than affected legs. Across the groups, energy stored in the NWB group was 74% of the WB group. The energy stored in affected legs was 80% of that in unaffected legs. Shock absorption was not significantly different across legs or groups. Irrespective of group, affected legs had significantly less stiffness (20-40%). While the augmentation of plaster with a Bohler iron to allow increased weight bearing had positive effects, deficits in affected compared to unaffected legs irrespective of group were notable, and should be addressed prior to participation in vigorous physical activities.

The differential effects of PNF versus passive stretch conditioning on neuromuscular performance

The effects of flexibility conditioning on neuromuscular and sensorimotor performance were assessed near to full knee extension (25°). Eighteen males who were randomly assigned into two groups underwent eight weeks (three-times per week) of flexibility conditioning (hip region/knee flexor musculature; dominant limb) involving either proprioceptive neuromuscular facilitation (PNF) (n=9) or passive stretching (PASS) (n=9). Both modes of flexibility conditioning are popular within contemporary exercise and clinical settings and have demonstrated efficacy in improving range of motion. The contralateral limb and a prior 'no exercise' condition were used as controls. The PNF and PASS modes of conditioning improved passive hip flexibility to a similar extent (mean 19.3% vs. baseline, intervention limb, p<0.01) but did not alter knee flexor strength (overall mean 309.6±81 N) or sensorimotor performance (force and positional errors: 2.3±8.2% and 0.48±7.1%). Voluntary and magnetically evoked electromechanical delays (EMDV and EMDE, respectively) were increased but to a greater extent following PASS compared to PNF (PASS: 10.8% and 16.9% lengthening of EMDV and EMDE, respectively vs. PNF: 3.2% and 6.2%, p<0.01).The attenuated change to electromechanical delay (EMD) performance during PNF conditioning suggests a preserved capability for rapid muscle activation, which is important in the maintenance of dynamic joint stability. That PNF was also equally efficacious in flexibility conditioning would suggest that this mode of flexibility training should be used over passive to help preserve dynamic joint stability capabilities at this extended and vulnerable joint position.

Acute lower extremity running kinematics after a hamstring stretch

CONTEXT

Limited passive hamstring flexibility might affect kinematics, performance, and injury risk during running. Preactivity static straight-leg raise stretching often is used to gain passive hamstring flexibility.

OBJECTIVE

To investigate the acute effects of a single session of passive hamstring stretching on pelvic, hip, and knee kinematics during the swing phase of running.

DESIGN

Randomized controlled clinical trial.

SETTING

Biomechanics research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-four male (age = 21.2 ± 1.4 years) and female (age = 21.3 ± 2.0 years) recreational athletes.

INTERVENTION(S)

Participants performed treadmill running pretests and posttests at 70% of their age-predicted maximum heart rate. Pelvis, hip, and knee joint angles during the swing phase of 5 consecutive gait cycles were collected using a motion analysis system. Right and left hamstrings of the intervention group participants were passively stretched 3 times for 30 seconds in random order immediately after the pretest. Control group participants performed no stretching or movement between running sessions.

MAIN OUTCOME MEASURE(S)

Six 2-way analyses of variance to determine joint angle differences between groups at maximum hip flexion and maximum knee extension with an α level of .008.

RESULTS

Flexibility increased between pretest and posttest in all participants (F(1,30) = 80.61, P < .001). Anterior pelvic tilt (F(1,30) = 0.73, P = .40), hip flexion (F(1,30) = 2.44, P = .13), and knee extension (F(1,30) = 0.06, P = .80) at maximum hip flexion were similar between groups throughout testing. Anterior pelvic tilt (F(1,30) = 0.69, P = .41), hip flexion (F(1,30) = 0.23, P = .64), and knee extension (F(1,30) = 3.38, P = .62) at maximum knee extension were similar between groups throughout testing. Men demonstrated greater anterior pelvic tilt than women at maximum knee extension (F(1,30) = 13.62, P = .001).

CONCLUSIONS

A single session of 3 straight-leg raise hamstring stretches did not change pelvis, hip, or knee running kinematics.

Reliability of manual versus automated techniques for assessing passive stiffness of the posterior muscles of the hip and thigh

The purpose of this study was to compare the reliability of passive stiffness, passive torque, range of motion (ROM), and electromyography (EMG) of the biceps femoris during passive thigh flexion motions intended to assess the ROM of the posterior muscles of the hip and thigh during manual versus automated assessment techniques. Eleven healthy men (mean ± s age = 22 ± 4 years; mass = 85 ± 12 kg; and height = 178 ± 4 cm) and nine healthy women (age = 19 ± 1 years; mass = 66 ± 15 kg; and height = 164 ± 5 cm) completed four randomly ordered passive straight-legged ROM assessments. Two ROM assessments were performed using a manual technique, which consisted of the primary investigator applying slow passive resistance against a load cell attached to the heel while the foot was moved toward the head. Two automated ROM assessments were also performed using a Biodex System 3 isokinetic dynamometer programmed in passive mode to move the foot toward the head at 0.087 rad · s(-1). The intraclass correlation coefficients (ICCs) for passive stiffness measured with the manual technique ranged from 0.81-0.86, while for the automated technique they were 0.72-0.92. Standard error of measurement (SEM) values for passive stiffness expressed as a percentage of the mean ranged from 15.5-21.7% for the manual and 17.8-23.7% for the automated technique. Both techniques (manual and automated) were comparably reliable across the three trials, which suggested that the manual technique could be applied outside the laboratory.

Acute effects of cold pack on mechanical properties of the quadriceps muscle in healthy subjects

PURPOSE

To examine the effects of local cooling on mechanical properties of the quadriceps muscle in healthy subjects.

SUBJECTS

Thirty-nine healthy subjects (27 women, 12 men, mean age 39, range 20-62) volunteered.

METHODS

A cold gel pack was applied to the quadriceps muscle for 20 min. Properties were quantified by analyzing the frequency (tension), decrement (elasticity) and stiffness of damped oscillations and the compliance of the muscle before, immediately after and after 15-min after cooling.

RESULTS

The largest responses immediately after cooling were seen in the oscillation decrement parameter, 7.9 (3.7-12.1) %, and in the compliance parameter, -7.5 (-9.8 to -5.3) %. Responses in the oscillation frequency, 6.5 (2.3-10.6) %, and stiffness parameters, 4.0 (0.8-7.1) %, were also statistically significant. The compliance still showed a -6.1 (-7.7 to -4.5) % decrease after the 15 min recovery phase, while no remaining alteration was found in the oscillation parameters.

CONCLUSION

The quadriceps muscle became tenser, stiffer, and less elastic as a result of cooling, and the mechanical properties were not fully recovered after 15 min. Careful warming-up is suggested after cooling to enable normalization of mechanical properties of the muscle and to avoid injuries.

Efeitos de um tratamento combinado (vitamina C pré-exercício e alongamento FNP, tratamento com ultrassom pós-exercício) sobre marcadores de dano muscular induzido por exercício

CONTEXTO: Várias estratégias de recuperação têm sido utilizadas na tentativa de minimizar os sintomas da dor muscular de início tardio (DMIT). Contudo, evidências científicas que apoiem este efeito profilático (pré-exercício) e terapêutico (pós-exercício) de um tratamento combinado (FNP e vitamina C, ultrassom) no dano muscular são inexistentes. OBJETIVO: Investigar os efeitos de um tratamento combinado (FNP e vitamina C, ultrassom) nos marcadores bioquímicos (níveis enzimáticos) e funcionais (ângulo do cotovelo, circunferência de braço, taxa de dor) de dano muscular induzido por exercício. MÉTODO: Amostra randomizada controlada. LOCAL: Laboratório da Universidade. PARTICIPANTES: Alunos universitários masculinos participaram voluntariamente do estudo, o qual não reportou nenhuma dor muscular de início tardio por no mínimo seis meses antes do estudo. Posteriormente, os sujeitos foram agrupados aleatoriamente em subgrupos com mão controle e mão experimental. INTERVENÇÃO(ÕES): Programa de exercício para indução de dano muscular induzido por exercício envolvendo o teste de bíceps Scott (contração excêntrica com duas mãos). PROCEDIMENTO(S) PRINCIPAL(IS): Circunferência de braço relaxado, circunferência de braço flexionado, ângulo de cotovelo em descanso, circunferência de antebraço, amplitude de movimento de cotovelo flexionado, amplitude de movimento de cotovelo estendido, dano muscular induzido por exercício, força máxima voluntária isométrica e isocinética foram registrados basal, imediatamente após exercício e 24, 48, 72 e 96 horas após exercício. RESULTADOS: O subgrupo experimental manifestou redução de sintomas de DMIT em menor amplitude de movimento de cotovelo flexionado e amplitude de movimento de cotovelo estendido, menor perda de força isométrica e isocinética voluntária máxima (P < 0,05) em comparação com o subgrupo controle. Contudo, nenhum efeito na circunferência de braço relaxado, circunferência de braço flexionado, ângulo de cotovelo em descanso ou circunferência de antebraço foi observado (P >0,05). CONCLUSÃO: Este tratamento combinado foi eficiente em contração máxima voluntária isométrica, dor muscular de início tardio e taxa de intensidade de dor ao longo do tempo. Finalmente, os resultados sugerem que os tratamentos combinados são eficientes na manutenção de força isométrica e diminuição de dor muscular de início tardio e taxa de intensidade de dor.

Comparison of active stretching technique in males with normal and limited hamstring flexibility

OBJECTIVE

(1) to analyse the accumulative effects of a 12-week active stretching program on hip flexion passive range of motion (HF-PROM), and (2) to compare whether participants with different PROM baseline scores (normal and limited hamstring flexibility) respond in the same way to stretching.

DESIGN

Repeated measures design.

SETTING

Controlled laboratory environment.

PARTICIPANTS

138 males were categorized according to hamstring flexibility in the unilateral passive straight-leg raise test (PSLR) and assigned to one of two groups: normal hamstring flexibility (≥80°) or limited hamstring flexibility (<80°). In each group, participants were randomly distributed into one of two treatment subgroups: (a) control or (b) active stretching. The active stretching subgroups performed 12 weeks of flexibility training, the control subgroups did not stretch.

MAIN OUTCOME MEASURES

HF-PROM was determined through the PSLR test.

RESULTS

Both stretching subgroups significantly improved (p < 0.01) their HF-PROM from baseline. The control subgroups did not.

CONCLUSIONS

12 weeks of an active stretching program performed 3 days per week with a daily stretch dose of 180 s improved HF-PROM in both populations (normal and limited hamstring flexibility). The stretching program was equally effective in terms of absolute improvement values for males with normal and limited hamstring flexibility.

Gender differences in both active and passive parts of the plantar flexors series elastic component stiffness and geometrical parameters of the muscle-tendon complex

Men are reportedly at higher risk of plantar flexor muscle injury and Achilles tendon ruptures than women. Biomechanical parameters are thought to play a role in the higher frequency of injury to males. One parameter is the stiffness of tissues; a stiff tissue cannot absorb sufficient energy with loading, and subsequently may be more likely to be injured. Thus, our purpose was to investigate the gender difference in the geometrical parameters of plantar flexor's muscle-tendon complex and the stiffness of both active and passive parts of the series elastic component (S(SEC1) and S(SEC2) , respectively). Using the alpha method on data obtained from quick stretches to the plantar flexors performed during isometric contractions, S(SEC1) and S(SEC2) were assessed. Plantar flexor muscles and Achilles tendon cross-sectional areas (CSA(TS) and CSA(AT) , respectively) were determined in young healthy men (n = 49) and women (n = 31). The findings showed that S(SEC2) was higher in men (p < 0.001), but this difference was not apparent when S(SEC2) was normalized to CSA(AT) (p > 0.05). In contrast, S(SEC1) was lower in men (p < 0.001) and remained so after normalization to CSA(TS) . Higher joint stiffness observed in men was notably influenced by lever arm length. Thus, the results of this study have implications for performance and injury.

Absolute reliability of five clinical tests for assessing hamstring flexibility in professional futsal players

OBJECTIVES

To examine the absolute reliability of five methods for estimating hamstring flexibility in professional futsal players.

DESIGN

Absolute reliability laboratory study (k=4).

METHODS

A total of 46 male futsal players (172.9±4.5 cm; 69.7±7.5 Kg) completed the study. All participants performed each measurement test twice in a randomized order on four different occasions. Absolute reliability was examined through typical percentage error, percentage change in the mean and intraclass correlations (ICC) as well as their respective confidence limits.

RESULTS

The findings showed high reliability for the sit and reach test (SRT) (4.48% typical error; 0.84% change in the mean, 0.95 ICC), toe touch test (TT) (5.89% typical error; 2.31% change in the mean, 0.89 ICC) and back-saver sit and reach test (BSSR) (3.73% typical error; 0.51% change in the mean, 0.97 ICC) compared to the passive straight leg raise test (PSLR) (7.6% typical error; 8.86% change in the mean, 0.77 ICC) and modified sit and reach test (MSR) (11.87% typical error; 7.64% change in the mean, 0.84 ICC) which showed moderate reliability.

CONCLUSIONS

An observed change larger than 6.72%, 7.55% and 5.59% for baseline SRT, TT and BSSR scores respectively would indicate that a real improvement in hamstring flexibility has occurred. In addition, the clinical reliability of PSLR and MSR are questioned and should be re-evaluated in future research studies.

Effects of flexibility training on eccentric exercise-induced muscle damage

PURPOSE

This study investigated whether flexibility training would attenuate muscle damage induced by maximal eccentric exercise.

METHODS

Thirty untrained young men were allocated to static stretching (SS), proprioceptive neuromuscular facilitation (PNF), or control group (n = 10 per group). The SS consisted of 30 sets of a 30-s standard SS with a 30-s rest between sets, and the PNF included 5 sets of the 30-s standard SS followed by 3 sets of three "contract-relax-agonist-contract" procedures. These were performed three times a week for 8 wk, and all subjects performed six sets of 10 maximal isokinetic (30°·s) lengthening contractions of the knee flexors after the 8-wk training or 8 wk after the baseline measures (control). Changes in indirect markers of muscle damage before and for 5 d after the eccentric exercise were compared among the groups.

RESULTS

The range of motion (ROM) of the hip joint increased by 25°, and the optimum angle of the knee flexors shifted (P < 0.05) to a longer muscle length by 10° after training, without significant differences between SS and PNF. No significant changes in these variables were evident for the control group. Compared with the control group, the SS and PNF groups showed significantly (P < 0.05) smaller decreases and faster recovery of knee flexor muscle strength and smaller changes in optimum angle, ROM, muscle soreness, and plasma creatine kinase activity and myoglobin concentration without significant differences between the groups. The preeccentric exercise ROM or optimum angle was significantly (P < 0.05) correlated with the changes in the muscle damage markers.

CONCLUSIONS

These results suggest that both SS and PNF training are effective in attenuating eccentric exercise-induced muscle damage and that flexible muscles are less susceptible to the damage.

Repeated muscle injury as a presumptive trigger for chronic masticatory muscle pain

skeletal muscles sustain a significant loss of maximal contractile force after injury, but terminally damaged fibers can eventually be replaced by the growth of new muscle (regeneration), with full restoration of contractile force over time. After a second injury, limb muscles exhibit a smaller reduction in maximal force and reduced inflammation compared with that after the initial injury (i.e., repeated bout effect). In contrast, masticatory muscles exhibit diminished regeneration and persistent fibrosis, after a single injury; following a second injury, plasma extravasation is greater than after a single injury and maximal force is decreased more than after the initial injury. Thus, masticatory muscles do not exhibit a repeated bout effect and are instead increasingly damaged by repeated injury. We propose that the impaired ability of masticatory muscles to regenerate contributes to chronic muscle pain by leading to an accumulation of tissue damage, fibrosis, and a persistent elevation and prolonged membrane translocation of nociceptive channels such as P2X(3) as well as enhanced expression of neuropeptides including CGRP within primary afferent neurons. These transformations prime primary afferent neurons for enhanced responsiveness upon subsequent injury thus triggering and/or exacerbating chronic muscle pain.

Changes in infraspinatus cross-sectional area and shoulder range of motion with repetitive eccentric external rotator contraction

BACKGROUND

Repetitive eccentric loading results in muscle damage and subsequent changes in muscle stiffness and edema accumulation, which manifest as reduced joint range of motion and increased muscle cross-sectional area. The purpose of the study was to evaluate changes in shoulder range of motion and the infraspinatus cross-sectional area with repetitive eccentric contraction.

METHODS

Twenty physically active participants performed 9 sets of 25 repetitions of eccentric external rotator contractions. The ultrasonographic measurement of the infraspinatus cross-sectional area, and shoulder internal/external rotation and horizontal adduction range of motion were measured before, immediately after, and 24h after the intervention.

FINDINGS

Infraspinatus cross-sectional area significantly increased from baseline immediately after exercise (P<0.001), and remained elevated from baseline at the 24-hour follow up (P<0.001). Internal rotation and horizontal adduction range of motion did not change significantly between baseline and post-exercise (P>0.05), but were significantly decreased at the 24-hour follow up from the baseline (internal rotation: P<0.001, horizontal adduction: P<0.001) and the immediate post-exercise (internal rotation: P=1.012, horizontal adduction: P=0.016).

INTERPRETATION

These changes observed after the eccentric contractions may have implications for injury development in pitchers, because 1) the infraspinatus endures repetitive eccentric loading with pitching and 2) decreased internal rotation and horizontal adduction range of motion have been linked to upper extremity injuries. However, since the muscle response after eccentric loading varies by the task and previous exposure to similar stress, future study needs to investigate the time course of recovery of the muscle cross-sectional area and range of motion after pitching in competitive pitchers.

Muscle hardness measurement by using ultrasound elastography: a feasibility study

BACKGROUND

Muscle hardening, including delayed onset muscle soreness, can be found after vigorous exercise. Some techniques for measuring muscle hardness have been proposed. Freehand ultrasound (US) elastography has been developed and applied to breast imaging.

PURPOSE

To evaluate the feasibility of US elastography for investigating changes in muscle hardness after eccentric exercise of the elbow flexor muscles.

MATERIAL AND METHODS

Six healthy male volunteers performed eccentric contractions of the elbow flexor muscles of their non-dominant arms. US elastography was performed by using 14-6 MHz linear array transducer combined with a stabilizer and a gel pack of reference agent. Color-coded elasticity images and the relative strain ratio of the biceps brachii muscle to the reference were obtained. To verify the US elastography measurements, a commercially available durometer was also employed. Both measurements were performed before, immediately after, and 1-4 days after exercise. The mean scores of strain ratios of the US elastography and durometer measurements were examined using repeated-measures ANOVA.

RESULTS

US elastography demonstrated significant muscle hardening and recovery after exercise (P<0.01). Muscle hardness increased up immediately after the exercise and continued to increase, peaking on day 2 post-exercise, and then decreased until day 4. The durometer indicated similar changes to US elastography. The control arms did not demonstrate any significant change.

CONCLUSION

US elastography is feasible to measure muscle hardness and to produce a two-dimensional hardness map of the muscle.

A prospective study of the relationship between lower body stiffness and hamstring injury in professional Australian rules footballers

BACKGROUND

Hamstring strains remain one of the most prevalent injuries in Australian Rules football. The authors prospectively examined the relationship between musculotendinous stiffness of the hamstring and leg stiffness with hamstring injury in professional Australian Rules footballers during the 2006 season.

HYPOTHESIS

Higher hamstring stiffness and leg stiffness are related to noncontact, soft tissue hamstring injury risk in professional Australian Rules footballers.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Unilateral hamstring stiffness and leg stiffness were assessed in 136 professional footballers in the month before the commencement of the competitive season. This information was then investigated relative to players who suffered noncontact, soft tissue hamstring injuries during either matches or training throughout the season to identify whether preseason stiffness was related to injury occurrence.

RESULTS

Fourteen tested players recorded acute, noncontact hamstring injuries, resulting in 3.3 ± 2.8 weeks of missed match play per injury. At preseason testing, the players who ended up sustaining a hamstring injury during the season recorded significantly higher mean hamstring stiffness (11%, P = .04) and leg stiffness (5%, P = .03). When considering the injured players, the leg stiffness of the involved limb was significantly higher than the noninjured players (P = .02), whereas hamstring stiffness was significantly higher on the noninvolved limb (P = .01). Further, those players who suffered a hamstring injury were significantly older than the noninjured players (P = .01).

CONCLUSION

It appears that a high bilateral hamstring stiffness and leg stiffness may be a determinant in the risk of sustaining a hamstring injury. Further, relatively lower hamstring stiffness in the involved limb of injured players appears to be associated with increased injury and may be related to a lack of strength. The information from stiffness assessment may allow medical staff to determine the hamstring risk status for individual players in team sports.

Concentric muscle contractions before static stretching minimize, but do not remove, stretch-induced force deficits

The effects of concentric contractions and passive stretching on musculotendinous stiffness and muscle activity were studied in 18 healthy human volunteers. Passive and concentric plantar flexor joint moment data were recorded on an isokinetic dynamometer with simultaneous electromyogram (EMG) monitoring of the triceps surae, real-time motion analysis of the lower leg, and ultrasound imaging of the Achilles-medial gastrocnemius muscle-tendon junction. The subjects then performed six 8-s ramped maximal voluntary concentric contractions before repeating both the passive and concentric trials. Concentric moment was significantly reduced (6.6%; P < 0.01), which was accompanied by, and correlated with ( r = 0.60–0.94; P < 0.05), significant reductions in peak triceps surae EMG amplitude (10.2%; P < 0.01). Achilles tendon stiffness was significantly reduced (11.7%; P < 0.01), but no change in gastrocnemius medialis muscle operating length was detected. The subjects then performed three 60-s static plantar flexor stretches before being retested 2 and 30 min poststretch. A further reduction in concentric joint moment (5.8%; P < 0.01) was detected poststretch at 90% of range of motion, with no decrease in muscle activity or Achilles tendon stiffness, but a significant increase in muscle operating length and decrease in tendon length was apparent at this range of motion ( P < 0.05). Thirty minutes after stretching, muscle activity significantly recovered to pre-maximal voluntary concentric contractions levels, whereas concentric moment and Achilles tendon stiffness remained depressed. These data show that the performance of maximal concentric contractions can substantially reduce neuromuscular activity and muscle force, but this does not prevent a further stretch-induced loss in active plantar flexor joint moment. Importantly, the different temporal changes in EMG and concentric joint moment indicate that a muscle-based mechanism was likely responsible for the force losses poststretch.

Effects of eccentric strength training on biceps femoris muscle architecture and knee joint range of movement

The aim was to determine whether eccentric strengthening changed the muscle architecture of human biceps femoris and consequently, knee range of motion. Twenty-two subjects were randomly assigned to control and experimental groups. The experimental group completed an eccentric strengthening programme for 8 weeks. Outcome measures included hamstring muscle strength (one repetition maximum), the passive knee extension test (PKE) (knee joint angle at which the onset of passive tension occurs), fascicle length (FL) and pennation angle (PA). One repetition maximum increased by 34% (P < 0.01), the PKE test revealed a 5% increase in joint range of motion (P = 0.01), FL increased by 34% (P = 0.01) and PA did not change (P = 0.38). This is the first report of an increase in FL in the biceps femoris following eccentric resistance training. In addition, the results might imply that this fascicle lengthening could lead to an increase in the range of motion of the knee. Clinical implications for rehabilitation and injury prevention are discussed.

The time course of musculotendinous stiffness responses following different durations of passive stretching

STUDY DESIGN

Repeated-measures experimental design.

OBJECTIVE

To examine the acute effects of different durations of passive stretching on the time course of musculotendinous stiffness (MTS) responses in the plantar flexor muscles.

BACKGROUND

Stretching is often implemented prior to exercise or athletic competition, with the intent to reduce the risk of injury via decreases in MTS.

METHODS AND MEASURES

Twelve subjects (mean +/- SD age, 24 +/- 3 years; stature, 169 +/- 12 cm; mass, 71 +/- 17 kg) participated in 4 randomly-ordered experimental trials: control with no stretching, 2 minutes (2min), 4 minutes (4min), and 8 minutes (8min) of passive stretching. The passive-stretching trials involved progressive repetitions of 30-second passive stretches, while the control trial involved 15 minutes of resting. MTS assessments were conducted before (prestretching), immediately after (poststretching), and at 10, 20, and 30 minutes poststretching on a Biodex System 3 isokinetic dynamometer.

RESULTS

MTS decreased (P<.05) immediately after all stretching conditions (2min, 4min, and 8min). However, MTS for the 2min condition returned to baseline within 10 minutes, whereas MTS after the 4min and 8min passive-stretching conditions returned to baseline within 20 minutes.

CONCLUSIONS

Practical durations of passive stretching resulted in significant decreases in MTS; however, these changes return to baseline levels within 10 to 20 minutes.

Análise da relação entre flexibilidade e rigidez passiva dos isquiotibiais

INTRODUÇÃO: Rigidez e flexibilidade são propriedades musculares freqüentemente consideradas como sinônimas na literatura, apesar de apresentarem diferenças com relação as suas definições. OBJETIVO: Investigar a contribuição da medida de flexibilidade dos isquiotibiais para a rigidez passiva deste grupo muscular. MÉTODOS: A rigidez e a flexibilidade foram avaliadas em 33 indivíduos saudáveis. Um dinamômetro isocinético registrava o torque passivo oferecido pelos isquiotibiais durante a extensão passiva do joelho, à velocidade de 5º/s. Durante os testes, foi feita a monitoração da atividade muscular para garantir silêncio eletromiográfico. A inclinação da reta torque x ângulo foi utilizada para determinar a rigidez total dos isquiotibiais. A amplitude de teste foi dividida em três porções para calcular a rigidez do 1º, 2º e 3º terços do movimento angular. A flexibilidade foi avaliada através do ângulo articular do joelho em que o movimento da alavanca foi interrompido pelo examinador ao perceber resistência à movimentação adicional e o participante relatar sensação de desconforto pelo alongamento dos isquiotibiais. Como tratamento estatístico, foram utilizadas análises de regressão simples. RESULTADOS: Análises de regressão demonstraram valores de correlação r = -0,48 (R² = 0,23; p = 0,005), r = -0,54 (R² = 0,29; p = 0,001), r = -0,46 (R² = 0,21; p = 0,007) e r = -0,45 (R² = 0,20; p = 0,008) entre flexibilidade e rigidez passiva total, 1º, 2º e 3º terços, respectivamente. CONCLUSÃO: Apesar de as associações entre as variáveis terem sido significativas, uma percentagem pequena da variabilidade da medida de rigidez passiva pode ser explicada pela flexibilidade. Conclui-se que essas propriedades não são sinônimas e devem ser analisadas de forma independente.

Review of exercise-induced muscle injury: relevance for athletic populations

Exercise-induced skeletal muscle injury is well understood as the product of unfamiliar or strenuous physical activity. Eccentric or lengthening actions are primarily responsible for inducing injury, which subsequently leads to a variety of signs and symptoms. Although significant research supports this finding, most observations are specific to untrained individuals. In addition, many protocols designed both to induce muscle injury and assess performance following the injury are dissimilar from those utilized by physically trained individuals or are impractical in relation to athletic performance or both. Therefore, difficulty may arise when extrapolating information, from the available literature and applying the findings to athletic populations. This review addresses the efficacy of applying our current understanding of exercise-induced skeletal muscle injury to a physically trained population as well as highlights concerns that require future investigation.

Effects of stretching on passive muscle tension and response to eccentric exercise

BACKGROUND

Stretching is used in an attempt to improve performance and reduce the risk of muscle injury, with little evidence to support its effectiveness.

HYPOTHESIS

Four weeks of static or ballistic stretching can attenuate the increased soreness and decreased flexibility seen after eccentric exercise.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-nine male subjects were randomly assigned to a static stretching, ballistic stretching, or control group. On each of 4 consecutive days, they completed 4 maximal range of motion stretches using a Cybex isokinetic dynamometer to passively stretch the hamstrings at 0.087 rad.s(-1) (5 deg.s(-1)). Stiffness from 0.87 to 1.48 rad (50 degrees -85 degrees ), peak range of motion, work absorption, peak resistive torque, and soreness were measured. Participants then completed 4 weeks of either static or ballistic stretching for a total stretching duration of 3600 seconds. After training, the 4 days of testing were repeated with an eccentric exercise task added after day 1.

RESULTS

Stretching groups had an increase in range of motion and stretch tolerance after 4 weeks of stretching, with no change in muscle stiffness, work absorption, or delayed onset muscle soreness. After eccentric exercise, they also had greater range of motion and stretch tolerance than did controls.

CONCLUSION

Both static stretching and ballistic stretching increase range of motion, most likely as a result of enhanced stretch tolerance rather than changes in muscle elasticity. Four weeks of stretching maintain range of motion and stretch tolerance in the days after eccentric exercise.

Dynamic soft tissue mobilisation increases hamstring flexibility in healthy male subjects

OBJECTIVES

The purpose of this study was to investigate the effect of dynamic soft tissue mobilisation (STM) on hamstring flexibility in healthy male subjects.

METHODS

Forty five males volunteered to participate in a randomised, controlled single blind design study. Volunteers were randomised to either control, classic STM, or dynamic STM intervention. The control group was positioned prone for 5 min. The classic STM group received standard STM techniques performed in a neutral prone position for 5 min. The dynamic STM group received all elements of classic STM followed by distal to proximal longitudinal strokes performed during passive, active, and eccentric loading of the hamstring. Only specific areas of tissue tightness were treated during the dynamic phase. Hamstring flexibility was quantified as hip flexion angle (HFA) which was the difference between the total range of straight leg raise and the range of pelvic rotation. Pre- and post-testing was conducted for the subjects in each group. A one-way ANCOVA followed by pairwise post-hoc comparisons was used to determine whether change in HFA differed between groups. The alpha level was set at 0.05.

RESULTS

Increase in hamstring flexibility was significantly greater in the dynamic STM group than either the control or classic STM groups with mean (standard deviation) increase in degrees in the HFA measures of 4.7 (4.8), -0.04 (4.8), and 1.3 (3.8), respectively.

CONCLUSIONS

Dynamic soft tissue mobilisation (STM) significantly increased hamstring flexibility in healthy male subjects.

Comparison of the symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys

The purpose of this study was to compare symptoms of exercise-induced muscle damage after an initial and repeated bout of plyometric exercise in men and boys. Ten boys (9–10 yr) and 10 men (20–29 yr) completed two bouts of eight sets of 10 plyometric jumps, 2 wk apart. Perceived soreness (0–10, visual analog scale), isometric strength of the quadriceps at six knee flexion angles, and countermovement jump and squat jump height were assessed before and at 30 min, 24 h, 48 h, and 72 h after each bout. All variables followed the expected patterns of change in men, with soreness peaking at 24–48 h (5.8 ± 1.7) and decrements in muscle function peaking at 30 min after the first bout (73–85% of baseline scores). Symptoms remained for 72 h after the first bout in men. In boys, symptoms were much less severe and peaked at 30 min (visual analog scale = 2.1 ± 1.8, functional decrements 87–92% of baseline) and, with the exception of soreness, returned to baseline after 24 h. After the second bout of plyometric exercise, the level of soreness and decrements in countermovement jump, squat jump, and isometric strength were lower, although the effect was stronger in men, in all cases. The results of this study suggest that although children may experience symptoms of muscle damage after intensive plyometric exercise, they are much less severe. A prior bout of plyometric exercise also appears to provide children with some protection from soreness after a subsequent bout of plyometric exercise. Explanations for milder symptoms of exercise-induced muscle damage in children include greater flexibility leading to less overextension of sarcomeres during eccentric exercise, fewer fast-twitch muscle fibers, and greater and perhaps more varied habitual physical activity patterns.

Muscle hardness characteristics of the masseter muscle after repetitive muscle activation: comparison to the biceps brachii muscle

The purpose of this study was to compare hardness characteristics of the masseter muscle to those of the biceps brachii muscle during repetitive muscle movements. Seventeen asymptomatic female subjects participated in this study. Each subject, on separate days, undertook a 5-minute unilateral chewing gum task on the right side and a 5-minute flexion-extension exercise on the right hand with a 2kg dumbbell. Using a handheld hardness meter, muscle hardness was measured in the right masseter and in the biceps brachii muscle at eight time points (before the task, immediately after the task, and at 1, 3, 5, 10, 30, and 60 minutes after the task), and the data obtained before and after the task on each muscle were compared. Comparisons of the normalized data were also performed between the two muscles at each time point. As a result, a significant increase in muscle hardness was seen at 1 minute after the task in the biceps brachii muscle (p=0.0093). In contrast, the masseter muscle showed a tendency to lower hardness, with the lowest point of hardness occurring at 10 minutes after the task (p = 0.0160). Between the two muscles, there was a difference in the normalized data immediately after the task, and at 1, 5, and 10 minutes after the task (0.01 <p<0.05). In conclusion, it was found that muscle hardness characteristics of the masseter muscle completely differed from those of the biceps brachii muscle after repetitive muscle activation.

The impact of stretching on sports injury risk: a systematic review of the literature

PURPOSE

We conducted a systematic review to assess the evidence for the effectiveness of stretching as a tool to prevent injuries in sports and to make recommendations for research and prevention.

METHODS

Without language limitations, we searched electronic data bases, including MEDLINE (1966-2002), Current Contents (1997-2002), Biomedical Collection (1993-1999), the Cochrane Library, and SPORTDiscus, and then identified citations from papers retrieved and contacted experts in the field. Meta-analysis was limited to randomized trials or cohort studies for interventions that included stretching. Studies were excluded that lacked controls, in which stretching could not be assessed independently, or where studies did not include subjects in sporting or fitness activities. All articles were screened initially by one author. Six of 361 identified articles compared stretching with other methods to prevent injury. Data were abstracted by one author and then reviewed independently by three others. Data quality was assessed independently by three authors using a previously standardized instrument, and reviewers met to reconcile substantive differences in interpretation. We calculated weighted pooled odds ratios based on an intention-to-treat analysis as well as subgroup analyses by quality score and study design.

RESULTS

Stretching was not significantly associated with a reduction in total injuries (OR = 0.93, CI 0.78-1.11) and similar findings were seen in the subgroup analyses.

CONCLUSION

There is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes. Further research, especially well-conducted randomized controlled trials, is urgently needed to determine the proper role of stretching in sports.

Le travail musculaire excentrique : intérêts dans la prise en charge thérapeutique du sportif

OBJECTIVES

To review the research on the effects and indications of eccentric muscular contraction in the athlete.

METHODS

We searched the Medline database using the key words eccentric and negative work for reports of eccentric muscular contraction published from 1993 to 2004.

RESULTS

The physiologic features of eccentric contraction remain unknown but significantly differ from concentric contraction. Eccentric contraction has a specific effect: during sports practice, it permits the muscular and tendinous complex to support strain and strengthens the muscular action of articular stabilization. But eccentric contraction produces injuries: delayed-onset muscle soreness, and muscle rupture and tendinous injuries such as luxation, rupture, and tendinitis.

CONCLUSION

Treatment and prevention must have controlled protocols. In therapy, eccentric contraction must be realized at progressive speeds and resistances. Prevention of tendinous injury necessitates quantifying eccentric activity during training.

Handle dynamics predictions for selected power hand tool applications

This study uses a previously developed single-degree-of-freedom mechanical model to predict the power hand tool operator handle kinematic response to impulsive reaction forces (Lin, 2001). The model considers the human operator as a lumped parameter passive mechanical system, consisting of stiffness, mass moment of inertia, and viscous damping elements. Six power nutrunners were operated by 9 volunteers (3 men, 6 women) in the laboratory, and corresponding handle kinematics were compared against model predictions. A full-factorial experiment considered torque buildup time and work location. Normalized forearm flexor EMG was measured to quantify muscle exertions and used to proportionally adjust the stiffness parameter. The measured handle displacement for actual tool operation strongly correlated to the model predictions (R = .98) for all handle configurations. The overall model prediction error was 3% for predicting tool handle responses to impulsive reaction forces for various tool and workstation parameters. This model should make it possible for designers to identify conditions that minimize the torque reaction experienced by power hand tool operators.

Neuromuscular function after exercise-induced muscle damage: theoretical and applied implications

Exercise-induced muscle damage is a well documented phenomenon particularly resulting from eccentric exercise. When eccentric exercise is unaccustomed or is performed with an increased intensity or duration, the symptoms associated with muscle damage are a common outcome and are particularly associated with participation in athletic activity. Muscle damage results in an immediate and prolonged reduction in muscle function, most notably a reduction in force-generating capacity, which has been quantified in human studies through isometric and dynamic isokinetic testing modalities. Investigations of the torque-angular velocity relationship have failed to reveal a consistent pattern of change, with inconsistent reports of functional change being dependent on the muscle action and/or angular velocity of movement. The consequences of damage on dynamic, multi-joint, sport-specific movements would appear more pertinent with regard to athletic performance, but this aspect of muscle function has been studied less often. Reductions in the ability to generate power output during single-joint movements as well as during cycling and vertical jump movements have been documented. In addition, muscle damage has been observed to increase the physiological demand of endurance exercise and to increase thermal strain during exercise in the heat. The aims of this review are to summarise the functional decrements associated with exercise-induced muscle damage, relate these decrements to theoretical views regarding underlying mechanisms (i.e. sarcomere disruption, impaired excitation-contraction coupling, preferential fibre type damage, and impaired muscle metabolism), and finally to discuss the potential impact of muscle damage on athletic performance.

Factors Associated with Recurrent Hamstring Injuries

A history of muscle injury represents a predominant risk factor for future insult in that muscle group. The high frequency of re-injury and persistent complaints after a hamstring strain comprise major difficulties for the athlete on return to athletic activities. Some of the risk factors associated with the possible recurrence of the injury are, in all probability, already implicated in the initial injury. One can distinguish between those events peculiar to the sport activity modalities (extrinsic factors) and other contributing factors based on the athletes individual features (intrinsic factors). For both categories, the persistence of mistakes or abnormalities in action represent an irrefutable component contributing to the re-injury cycle. Additional factors leading to chronicity can come from the first injury per se through modifications in the muscle tissue and possible adaptive changes in biomechanics and motor patterns of sporting movements. We emphasise the role of questionable approaches to the diagnosis process, drug treatment or rehabilitation design. To date, the risk factors examined in the literature have either been scientifically associated with injury and/or speculated to be associated with injury. In this context, quantifying the real role of each factor remains hypothetical, the most likely ones corresponding to inadequate warm-up, invalid structure and the content of training, muscle tightness and/or weakness, agonist/antagonist imbalances, underestimation of an extensive injury, use of inappropriate drugs, presence of an extensive scar tissue and, above all, incomplete or aggressive rehabilitation. Such a list highlights the unavoidable necessity of developing valid assessment methods, the use of specific measurement tools and more rigorous guidelines in the treatment and rehabilitation. This also implies a scientific understanding as well as specifically qualified medical doctors, physiotherapists and trainers acting in partnership.

Stretching and Injury Prevention

It is generally accepted that increasing the flexibility of a muscle-tendon unit promotes better performances and decreases the number of injuries. Stretching exercises are regularly included in warm-up and cooling-down exercises; however, contradictory findings have been reported in the literature. Several authors have suggested that stretching has a beneficial effect on injury prevention. In contrast, clinical evidence suggesting that stretching before exercise does not prevent injuries has also been reported. Apparently, no scientifically based prescription for stretching exercises exists and no conclusive statements can be made about the relationship of stretching and athletic injuries. Stretching recommendations are clouded by misconceptions and conflicting research reports. We believe that part of these contradictions can be explained by considering the type of sports activity in which an individual is participating. Sports involving bouncing and jumping activities with a high intensity of stretch-shortening cycles (SSCs) [e.g. soccer and football] require a muscle-tendon unit that is compliant enough to store and release the high amount of elastic energy that benefits performance in such sports. If the participants of these sports have an insufficient compliant muscle-tendon unit, the demands in energy absorption and release may rapidly exceed the capacity of the muscle-tendon unit. This may lead to an increased risk for injury of this structure. Consequently, the rationale for injury prevention in these sports is to increase the compliance of the muscle-tendon unit. Recent studies have shown that stretching programmes can significantly influence the viscosity of the tendon and make it significantly more compliant, and when a sport demands SSCs of high intensity, stretching may be important for injury prevention. This conjecture is in agreement with the available scientific clinical evidence from these types of sports activities. In contrast, when the type of sports activity contains low-intensity, or limited SSCs (e.g. jogging, cycling and swimming) there is no need for a very compliant muscle-tendon unit since most of its power generation is a consequence of active (contractile) muscle work that needs to be directly transferred (by the tendon) to the articular system to generate motion. Therefore, stretching (and thus making the tendon more compliant) may not be advantageous. This conjecture is supported by the literature, where strong evidence exists that stretching has no beneficial effect on injury prevention in these sports. If this point of view is used when examining research findings concerning stretching and injuries, the reasons for the contrasting findings in the literature are in many instances resolved.