The effects of 6-week home-based static stretching, dynamic stretching, or eccentric exercise interventions on muscle-tendon properties and functional performance in older women.

Background: Joint inflexibility is acknowledged as a significant contributor to functional limitations in the older adult, with lengthening-type exercises identified as a potential remedial approach. Nevertheless, the responses to eccentric exercise in female older adults have not been extensively studied especially in home-based environment. Here, we aimed to assess the effectiveness of home-based static stretching (ST), dynamic closed-chain stretching (DCS), or eccentric exercise (ECC) interventions on flexibility, musculotendinous architecture, and functional ability in healthy older women. Methods: We randomly assigned 51 healthy older women (age 65.9 ± 3.4 years) to one of three interventional exercise groups: DCS (N = 17), ECC (N = 17), or ST (N = 17). The training was performed 3 times a week for 6 weeks. The participants' musculotendinous stiffness, fascicle length, eccentric strength, and functional capacities were measured before the intervention, after 6 weeks of exercise, and at a 1-month follow-up. Results: The results showed that all three interventions improved hamstring flexibility and passive ankle dorsiflexion (p < 0.001), with increased biceps femoris and medial gastrocnemius fascicle length (p < 0.01). However, there was no significant change in musculotendinous stiffness. The ECC intervention produced a greater improvement in knee flexor and calf eccentric peak torque (p < 0.05), and gait speed (p = 0.024) than the other two interventions. The changes in flexibility and knee flexor strength remained for up to 4 weeks after detraining. Conclusion: In conclusion, the present study suggests that home-based ECC may be more beneficial in enhancing physical capacities in older women compared with either DCS or SS interventions.

Effect of Whole-body Vibration frequency on muscle tensile state during graded plantar flexor isometric contractions.

Background: Acute physiological and biomechanical alterations have been reported following whole-body vibration (WBV). Stiffening of muscles has only been anecdotally reported in response to WBV. Accordingly, this study investigated active plantar flexor muscle stiffness in response to a single WBV bout at four mechanical vibration frequencies. Methods: Thirteen healthy adults (37.1 ± 14.4 years old) randomly received WBV in 4 different frequencies (6, 12, 24, and 0 Hz control) for 5 min. Shear wave speed (SWS) in longitudinal and transverse projections, architecture, and electric muscle activity were recorded in the medial gastrocnemius (MG) and soleus (SOL) muscle during graded plantar flexor contraction. Subjective rating of perceived muscle stiffness was assessed via Likert-scale. Results: SWS of the MG at rest was enhanced in response to 5 min of 24 Hz WBV (p = 0.025), while a small reduction in SOL SWS was found during contraction (p = 0.005) in the longitudinal view. Subjective stiffness rating was increased following 12 Hz intervention. After 24 Hz WBV, pennation angle for MG was decreased (p = 0.011) during contraction. As a secondary finding, plantar flexor strength was significantly increased with each visit, which, however, did not affect the study's main outcome because of balanced sequence allocation. Conclusion: SWS effects were solely limited to 24 Hz mechanical vibration and in the longitudinal projection. The observed effects are compatible with an interpretation by post-activation potentiation, warm-up, and force-distribution within the triceps surae muscles following 5 min WBV. The outcome may suggest SWS as a useful tool for assessing acute changes in muscle stiffness.

The effects of high-velocity hamstring muscle training on injury prevention in football players.

Background: Explosive and fast body movements, sprints, jumps and quick changes of direction, which are characteristic of the football training, place considerable strain on the hamstring muscles. Due to the high occurrence of hamstring injuries, new preventive strategies are required that focus on high-velocity training. The purpose was to assess the effectiveness of high-velocity elastic-band training in reducing the occurrence of hamstring injuries in football players. Methods: Male football players from 15 teams (n = 319) playing in national competitions participated in this study. The players were involved in a 5-week exercise period in either the intervention group (INT) or the control group (CON), with a follow-up period of ∼4 months where hamstring injuries and exposure time were recorded. The INT group had two to three sessions per week of elastic-band training with low-load, high-velocity leg curls while lying prone; the CON group performed self-paced football-specific drills. Results: The incidence rate of hamstring injuries was 6.5% in the INT group (8 out of 123 players) and 9.2% in the CON group (18 out of 196 players). Although the INT group showed almost 1/3 reduction in hamstring injury incidence compared to the CON group, the difference was not statistically significant (p > 0.05). Moreover, no differences (p > 0.05, odds ratio [OR] = trivial-to-small) in distribution between the groups were found in hamstring injury characteristics (leg dominance and mechanism) except for the distribution of injuries that occurred during matches or training (p = 0.036; OR = 6.14, moderate). Conclusion: The program of high-velocity elastic-band training did not prove to be effective in preventing hamstring muscle injuries in football players despite displaying some positive indications that could be considering when creating injury prevention programs.

Hamstrings fascicle length and physical performance changes after a single bout of dynamic stretching or neurodynamic gliding in healthy young and older adults.

INTRODUCTION: The physiological and structural alterations have been less reported in response to dynamic stretching (DS) or neurodynamic nerve gliding (NG). Accordingly, this study investigated the changes in fascicle lengths (FL), popliteal artery velocity, and physical fitness in response to a single bout of DS or NG. METHODS: The study included 15 healthy young adults (20.9 ± 0.7 yrs) and 15 older adults (66.6 ± 4.2 yrs) who randomly performed three different interventions (DS, NG, and rest control) for 10 min and 3 days apart. The biceps femoris and semitendinosus FL, popliteal artery velocity, sit and reach (S&R), straight leg raise (SLR), and fast walking speed were measured before and immediately after the intervention. RESULTS: After NG intervention, S&R was largely greater by 2 cm (1.2, 2.8 cm) and 3.4 cm (2.1, 4.7 cm) with largely increased SLR angles of 4.9° (3.7°, 6.1°) and 4.6° (3.0°, 6.2°) with all p < 0.001 for the older adults and young groups, respectively. A similar magnitude improvement in the S&R and SLR testing was also seen for both groups after DS (p < 0.05). Moreover, no changes were seen in FL, popliteal artery velocity, fast gait speed, and age effect following all three intervention occasions. CONCLUSION: Stretching with DS or NG immediately increased flexibility, which appeared to be largely due to changes in stretch tolerance rather than an increase in fascicle length. Furthermore, age dependency in response to stretching exercise was not seen in the present study.

Associations between Muscle-Tendon Morphology and Functional Movements Capacity, Flexibility, and Balance in Older Women.

Loss of functional movement capacity in older adults is related to adverse changes in musculotendinous morphology, but this relationship is poorly understood. This study examined the associations between musculotendinous morphology and functional movements, flexibility, and balance ability. Ninety-nine older women (66.6 ± 4.6 years, body mass index 23.5 ± 3.3 kg∙m−2) were recruited from Chonburi Province, Thailand. During one 90-min visit, muscle ultrasound imaging of vastus lateralis, biceps femoris, and medial gastrocnemius muscles, and tendon ultrasonography of the Achilles tendon and patellar tendon were performed. Measures were also obtained for the straight leg raise, passive dorsiflexion, balance, and functional tests (Five Times Sit to Stand (5TSTS), Timed Up and Go (TUG), 10-Meter Fast Walk Test (10-MFWT), and 6-Minute Walk Test (6-MWT)). The results specify that functional movement performance correlates most strongly with medial gastrocnemius muscle thickness (5TSTS (r = −0.26), TUG (r = −0.44), 10-MFWT (r = 0.41), and 6-MWT (r = 0.48) all p < 0.05) and that vastus lateralis muscle thickness and medial gastrocnemius muscle thickness correlate positively with balance ability (r = 0.24, 0.34; p < 0.05) and negatively with fear of falling. It appears that muscle mass, rather than other morphological parameters, such as muscle quality or fascicle length, is the main factor affecting the susceptibility of older women to frailty.

Combined Use of Transcutaneous Electrical Nerve Stimulation and Short Foot Exercise Improves Navicular Height, Muscle Size, Function Mobility, and Risk of Falls in Healthy Older Adults.

Electrical stimulation is an established method that is used to improve muscle strength. The present study compared changes in the navicular drop test (NDT), muscle size, the five times sit to stand (5TSTS) test, the timed up and go (TUG) test, and the risk of falls in response to transcutaneous electrical nerve stimulation (TENS) plus short foot exercise (SFE) and SFE alone in 68 healthy elderly participants aged 65−75 years. Participants were randomly assigned to two groups: TENS plus SFE and SFE alone (with sham TENS). Measurements of NDT, muscle size, 5TSTS, TUG, and risk of falls were made before and after 4 weeks of training. The NDT was significantly improved by a median of 0.31 mm in the TENS plus SFE group and 0.64 mm in the SFE alone group (p < 0.001). Similarly, there was a significant improvement in Falls Efficacy Scale International (FES-I), 5TSTS, and TUG for both groups (p < 0.001). The abductor hallucis muscle size increased by 0.23 cm2 in the TENS plus SFE group and 0.26 cm2 in the SFE alone group (p < 0.001). There were no significant differences between the two groups for any variables (p > 0.05) except TUG, which showed a greater improvement in the TENS plus SFE group (p = 0.008). Our findings demonstrated that TENS plus SFE and SFE alone improved intrinsic foot muscle size. However, TENS plus SFE tended to improve NDT more than SFE alone, particularly in cases of severe muscle weakness. Thus, the combined use of TENS plus SFE could be recommended for muscle strengthening and balance programs for fall prevention in older adults.

The Effects of Electrical Stimulation Program on Navicular Height, Balance, and Fear of Falling in Community-Dwelling Elderly.

INTRODUCTION: Intrinsic foot muscle weakness is a crucial cause of balance deficit in the elderly, which leads to a limited range of motion from the fear of falling and subsequently decreases the quality of life. Muscle strengthening via transcutaneous electrical stimulation (TENS) is an effective intervention; however, its effects on elderly people have rarely been reported. This study was conducted to investigate the effects of TENS on navicular height, balance, and fear of falling. METHOD: In this study, forty-eight participants aged 65-75 years were included and were randomly divided into two groups: the TENS and control groups. Before and after 4 weeks of training, navicular height, balance, and fear of falling were measured. RESULT: After 4 weeks of training, navicular height significantly increased in both groups (p < 0.05); however, the increase was higher in the TENS group (p = 0.035). The TENS group had a better improvement in balance in all four directions-front, back, left, and right (p < 0.05). However, postural balance improvements in the control group were observed in three directions only-front, back, and left (p < 0.05)-without any significant difference between the two groups. Furthermore, the TENS group decreased the scale of fear of falling after 4 weeks of training (p = 0.039). CONCLUSION: In summary, the results of this study can be used as part of the muscle strengthening via ES for decreasing the risk of falls or fear of falling in the elderly.

Response of Knee Extensor Muscle-Tendon Unit Stiffness to Unaccustomed and Repeated High-Volume Eccentric Exercise.

The purposes of this study were to investigate the muscle-tendon unit stiffness response and to compare the stiffness with those of other indirect markers induced by two bouts of unaccustomed eccentric exercise. Eleven untrained men performed two bouts of 200 maximal eccentric contractions of the right quadriceps 4 weeks apart. Changes in stiffness, pain evoked by stretching and pressure, plasma creatine kinase (CK) activity, and muscle thickness were followed for 7 days after each bout. Stiffness and pain peaked immediately and 1 day after the first exercise bout, whereas CK and thickness were highest 4 and 7 days after the first exercise bout, respectively (p < 0.05 for all). Muscular pain, thickness, and stiffness responses were lower by 53.3%, 99%, and 11.6%, respectively, after the repeated bout compared to after the first bout (p < 0.05 for all), while CK activity response did not differ significantly between bouts. High responders for an increase in muscle-tendon unit stiffness showed a repeated-bout effect for stiffness, pain, and CK activity (by 29%, 65%, and 98%, p < 0.05 for all), but the repeated-bout effect was not that clear in low responders. These findings suggest that a repeated eccentric exercise bout effect on stiffness in quadriceps is mostly not associated with muscle pain and CK activity, but there are large individual differences.

Immediate effects of neurodynamic nerve gliding versus static stretching on hamstring neuromechanical properties.

PURPOSE: We investigated the immediate effects of neurodynamic nerve gliding (ND) on hamstring flexibility, viscoelasticity, and mechanosensitivity, compared with traditional static stretching (ST). METHODS: Twenty-two physically active men aged 21.9 ± 1.9 years were divided randomly into two equal intervention groups using ST or ND. An isokinetic dynamometer was used to measure the active knee joint position sense, perform passive knee extension, record the passive extension range of motion (ROM) and the passive-resistive torque of hamstrings. Stiffness was determined from the slope of the passive torque-angle relationship. A stress relaxation test (SRT) was performed to analyze the viscoelastic behavior of the hamstrings. The passive straight leg raise (SLR) test was used to evaluate hamstring flexibility. RESULTS: A significant interaction was observed for ROM and passive ultimate stiffness, reflected by an increase in these indicators after ND but not after SD. SLR increased significantly in both groups. After ST, a significantly faster initial stress relaxation was observed over the first 4 s. than after ND. There was no significant change in the active knee joint position sense. CONCLUSIONS: ND provided a slightly greater increase in hamstring extensibility and passive stiffness, possibly by decreasing nerve tension and increasing strain in connective tissues than ST. The ST mostly affected the viscoelastic behavior of the hamstrings, but neither intervention had a significant impact on proprioception.

Low frequency fatigue and changes in muscle fascicle length following eccentric exercise of the knee extensors.

NEW FINDING: What is the central question of this study? Does low frequency muscle fatigue indicate a failure of excitation-contraction coupling after eccentric exercise, or is it simply due to a change in muscle length? What is the main finding and its importance? The low to high frequency muscle fatigue ratio was relatively insensitive to changes in muscle length, and any changes in length following eccentric exercise were far too small to account for the high degree of low frequency fatigue. The results strengthen the suggestion that the early loss of force following eccentric exercise is due to a deficit of excitation-contraction coupling. ABSTRACT: Development of long lasting fatigue (low frequency fatigue; LFF), assessed as the ratio of forces at 20 and 100 Hz stimulation, suggests the early phase of muscle damage caused by eccentric exercise is due to a deficit of excitation-contraction coupling. However, this could be caused by a change of muscle length. Eleven men (21.3 ± 2.0 years) performed 200 maximum eccentric knee extensions (30-110 deg flexion). Force generated by 20 and 100 Hz stimulation and maximum isometric force (MIF) were determined at knee angles 50, 70 and 90 deg before and immediately after the exercise. Vastus lateralis fascicle length (FL) was measured by ultrasound of resting and contracting muscle. Peak MIF (829 ± 119 N) was at 70 deg knee flexion, falling to 486 ± 180 N (P < 0.001) after exercise, but with no change in optimum angle. FLs at rest were unaffected by eccentric exercise, but during contraction they were on average 8.8% (95% CI: 4.1, 13.5%, P = 0.002) longer after exercise. Before exercise, the 20/100 ratio increased with muscle length, from 0.69 ± 0.09 at 50 deg, 0.72 ± 0.05 at 70 deg and 0.80 ± 0.08 at knee angle 90 deg (P < 0.001). After eccentric exercise the 20/100 ratio was reduced to 0.29 ± 0.08 at 50 deg, 0.27 ± 0.04 at 70 deg and 0.34 ± 0.04 at 90 deg (P < 0.001). The 20/100 ratio was relatively insensitive to changes in muscle length and the decrease following eccentric exercise was far greater than might be caused by any changes in muscle length after eccentric exercise. The results show that LFF following eccentric exercise is not due to change in muscle length and strengthen the suggestion that it represents a deficit in excitation-contraction coupling.

The contribution of low-frequency fatigue to the loss of quadriceps contractile function following repeated drop jumps.

NEW FINDINGS: What is the central question of this study? Why do some subjects recover slowly following a bout of eccentric exercise and why is recovery faster following a repeated bout? What is the main finding and its importance? The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed form of damage. Differences in the delayed damage process largely accounted for the differences in the rate of torque recovery between subjects after a first bout and it was suppression of the delayed damage which accounted for the faster recovery following a repeated bout of eccentric exercise. ABSTRACT: The purpose of this study was to determine the extent to which low-frequency fatigue (LFF) accounts for the loss of quadriceps strength and time course of recovery following a series of drop jumps (DJs). Seventeen female subjects (20.8 ± 1.4 years) undertook 100 DJs, which were repeated 4 weeks later. Maximum isometric torque (MIT) and the ratio of torque generated by 20 and 100 Hz electrical stimulation (20/100), as a measure of LFF, were measured over 7 days following each series of DJs. After the first series the 20/100 ratio fell to a greater extent than MIT (to 35 ± 8.7% and 69 ± 11%, respectively) but recovered over 2-3 days, while MIT showed little recovery over this time. Changes of the 20/100 ratio were similar between subjects with fast or slow MIT recovery. Following the second series of DJs, changes in the 20/100 ratio were similar to those of the first bout and there were no differences between fast and slow recovering subjects. MIT, however, recovered more rapidly than after the first bout; the faster recovery was confined to the subjects who recovered slowly following the first bout. The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed, form of damage. The latter largely accounted for the differences in MIT recovery between subjects after the first bout, while suppression of the delayed damage accounted for the faster recovery following the repeated bout.

Slow torque recovery after eccentric exercise and the repeated bout effect; the role of primary and secondary muscle damage.

OBJECTIVES: To determine the role of primary and secondary damage in the variation between people of maximum voluntary contraction (MVC) torque recovery following eccentric exercise and the faster recovery following a repeated bout of exercise. METHODS: Twenty-one healthy, active but untrained young female subjects undertook eccentric exercise of the elbow flexors and 11 repeated the exercise 28 days later. Changes of MVC torque and creatine kinase (CK) were followed for 7 days after each bout of exercise. RESULTS: Following the first bout, 45% of subjects showed a continuing decline in MVC torque, suggesting secondary damage, which was correlated with a large delayed CK release (R2=0.54, p<0.001). After the second bout of exercise, the initial MVC torque loss was similar to that after the first bout while torque recovery was faster, but only for the previously slow recovering subjects. Comparing the time course of MVC torque recovery of first and second bouts suggests secondary damage develops over 4 days. CONCLUSIONS: The data are consistent with primary damage being similar between subjects and unaffected by the repeated bout while it is secondary damage which accounts for differences in MVC torque recovery and is suppressed following a repeated bout of exercise.

The relationship between stiffness and pain following unaccustomed eccentric exercise: the effects of gentle stretch and repeated bout.

PURPOSE: To determine how muscle stiffness and pain which develop after eccentric exercise are affected by gentle stretching and repeated exercise. METHODS: Twenty-one healthy female participants undertook eccentric exercise of the elbow flexors and changes in resting elbow flexion angle (REFA; a measure of muscle stiffness), pain on stretch scale, pain elicited by pressure (PPT pain, a measure of mechanoreceptor hypersensitivity), and upper arm girth were followed for 7 days after exercise. The effects of gentle passive stretching on pain and muscle stiffness were investigated 2 and 4 days after exercise. Eleven participants also repeated the exercise with the same arm 6 weeks after the first bout. RESULTS: There was a significant relationship between the pain on stretch scale and increased REFA (day 4; R2 = 0.65, p < 0.001), whereas there was no relationship between REFA and PPT pain. REFA was reduced by passive stretching and pain on stretch scale was also reduced from 3.0 (1.4, 5.1) to 0.75 (0.0, 2.0) [median (IQR), p = 0.01]. PPT pain was unaffected by the passive stretching, as was muscle swelling. Following the repeated bout, increases in REFA were much reduced, as was pain on stretch scale (p = 0.02). However, PPT pain was not significantly different between the two bouts of exercise. CONCLUSIONS: The results indicate that reductions in pain on stretch scale, either by gentle passive stretching or as the result of repeated exercise, are primarily due to reductions in muscle stiffness which develops after eccentric exercise, whereas mechanoreceptor hypersensitivity is relatively unaffected.

The effects of 4 weeks stretching training to the point of pain on flexibility and muscle tendon unit properties.

PURPOSE: The purpose of this study was to compare the benefits and possible problems of 4 weeks stretching when taken to the point of pain (POP) and to the point of discomfort (POD). METHODS: Twenty-six physically active women (20 ± 1.1 years) took part in group-based stretching classes of the hamstring muscles, 4 times per week for 4 weeks, one group one stretching to POD, the other to POP. Passive stiffness, joint range of motion (ROM), maximal isometric torque and concentric knee flexion torque, were measured before training and 2 days after the last training session. RESULTS: Hip flexion ROM increased by 14.1° (10.1°-18.1°) and 19.8° (15.1°-24.5°) and sit-and-reach by 7.6 (5.2-10.0) cm and 7.5 (5.0-10.0) cm for POD and POP, respectively (Mean and 95% CI; p < 0.001 within group; NS between groups), with no evidence of damage in either group. Despite the large increases in flexibility there were no changes in either compliance or viscoelastic properties of the muscle tendon unit (MTU). CONCLUSION: Hamstrings stretching to POP increased flexibility and had no detrimental effects on muscle function but the benefits were no better than when stretching to POD so there is no justification for recommending painful stretching. The improvements in flexibility over 4 weeks of stretching training appear to be largely due to changes in the perception of pain rather than physical properties of the MTU although less flexible individuals benefited more from the training and increased hamstring muscle length.

The acute benefits and risks of passive stretching to the point of pain.

PURPOSE: This study evaluated the acute effects of two different stretch intensities on muscle damage and extensibility. METHODS: Twenty-two physically active women (age 20 ± 1.0 years) were divided into two matched groups and undertook eight sets of 30-s passive hamstring stretching. One group stretched to the point of discomfort (POD) and the other to the point of pain (POP). Hamstring passive torque, sit and reach (S&R), straight leg raise (SLR), and markers of muscle damage were measured before, immediately after stretching and 24 h later. RESULTS: S&R acutely increased and was still increased at 24 h with median (interquartile range) of 2.0 cm (0.5-3.75 cm) and 2.0 cm (0.25-3.0 cm) for POP and POD (p < 0.05), respectively, with no difference between groups; similar changes were seen with SLR. Passive stiffness fully recovered by 24 h and there was no torque deficit. A small, but significant increase in muscle tenderness occurred at 24 h in both groups and there was a very small increase in thigh circumference in both groups which persisted at 24 h in POP. Plasma CK activity was not raised at 24 h. CONCLUSION: Stretching to the point of pain had no acute advantages over stretching to the discomfort point. Both forms of stretching resulted in very mild muscle tenderness but with no evidence of muscle damage. The increased ROM was not associated with changes in passive stiffness of the muscle but most likely resulted from increased tolerance of the discomfort.