Activity-Induced Increase in Achilles Tendon Blood Flow Is Age and Sex Dependent.

BACKGROUND: Previous research of a young adult population identified a lower increase in Achilles tendon blood flow immediately after a running activity as a significant predictor for the development of Achilles tendinopathy (AT). Furthermore, advancing age is often mentioned as a risk factor for the development of AT, and the highest incidence for AT is reported to occur in middle-aged recreational male athletes. PURPOSE: To investigate the effect of age, sex, and type of physical activity on the increase in Achilles tendon blood flow. STUDY DESIGN: Controlled laboratory study. METHODS: Blood flow measurements of 33 subjects aged 18 to 25 years and 30 subjects aged 40 to 55 years were obtained before and after 4 physical activities performed in randomized order: running, cycling, dynamic stretching, and rope skipping. Blood flow measurements of the Achilles tendon were performed before, immediately after, 5 minutes after, and 10 minutes after the physical activities. The effect of age, sex, and physical activities on the increase in blood flow was investigated with linear mixed models. RESULTS: The results of this study identified that running, rope skipping, and cycling resulted in a significant increase in tendon blood flow ( P ≤ .001), whereas stretching did not. Prominent was the finding that the increase in blood flow after activity was significantly lower in the older population as compared with the younger population ( P < .001). Furthermore, male participants in the older group showed a significantly lower increase in tendon blood flow than did their female counterparts ( P = .019). CONCLUSION: This study identified that sex and age significantly influence the increase in blood flow after activity, possibly explaining the increased risk for AT among middle-aged recreational athletes. CLINICAL RELEVANCE: This study possibly identified one of the mechanisms explaining why an older male population is at increased risk for developing AT. Given that the lower increase in blood flow is an identified risk factor according to previous research, preventative measures should focus on improving this blood flow during physical activity in the physically active older male population. Registration: NCT03218605 ( ClinicalTrials.gov identifier).

The Role of the Vascular and Structural Response to Activity in the Development of Achilles Tendinopathy: A Prospective Study.

BACKGROUND: Several risk factors have been suggested in the development of Achilles tendinopathy, but large-scale prospective studies are limited. PURPOSE: To investigate the role of the vascular response to activity of the Achilles tendon, tendon thickness, ultrasound tissue characterization (UTC) of tendon structure, and foot posture as possible risk factors in the development of Achilles tendinopathy. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: The study began with 351 first-year students at Ghent University. After 51 students were excluded, 300 were tested in the academic years 2013-2014 and 2014-2015 and were followed prospectively for 2 consecutive years by use of a multilevel registration method. Of those, 250 students were included in the statistical analysis. At baseline, foot posture index and UTC were investigated bilaterally. Blood flow and tendon thickness were measured before and after a running activity. Cox regression analyses were performed to identify significant contributors to the development of Achilles tendinopathy. RESULTS: During the 2-year follow-up, 27 of the included 250 participants developed Achilles tendinopathy (11%). Significant predictive effects were found for female sex and blood flow response after running ( P = .022 and P = .019, respectively). The risk of developing Achilles tendinopathy increased if the blood flow increase after running was reduced, regardless of sex, foot pronation, and timing of flow measurements. The model had a predictive accuracy of 81.5% regarding the development of Achilles tendinopathy, with a specificity of 85.0% and a sensitivity of 50.0%. CONCLUSION: This prospective study identified both female sex and the diminished blood flow response after running as significant risk factors for the development of Achilles tendinopathy. UTC of tendon structure, Achilles tendon thickness, and foot posture did not significantly contribute to the prediction of Achilles tendinopathy. A general evaluation of tendon structure by UTC, measurement of tendon thickness, or determination of the foot posture index will not allow clinicians to identify patients at risk for developing Achilles tendinopathy. Furthermore, it may be possible to improve blood flow after activity by using noninvasive techniques (such as prostaglandins, compression stockings, heat, massage, and vibration techniques). These techniques may be useful in the prevention and management of Achilles tendinopathy, but further research is needed.

Does adding heavy load eccentric training to rehabilitation of patients with unilateral subacromial impingement result in better outcome? A randomized, clinical trial.

PURPOSE: To investigate superior value of adding heavy load eccentric training to conservative treatment in patients with subacromial impingement. METHODS: Sixty-one patients with subacromial impingement were included and randomly allocated to the traditional rotator cuff training (TT) group (n = 30, mean age = 39.4 ± 13.1 years) or traditional rotator training combined with heavy load eccentric training (TT + ET) group (n = 31, mean age = 40.2 ± 12.9 years). Isometric strength was measured to abduction at 0°, 45° and 90° of scapular abduction and to internal and external rotation. The SPADI questionnaire was used to measure shoulder pain and function. Patients rated subjective perception of improvement. Outcome was assessed at baseline, at 6 and 12 weeks after start of the intervention. Both groups received 9 physiotherapy treatments over 12 weeks. At home, the TT group performed traditional rotator cuff strengthening exercises 1x/day. The TT + ET group performed the same exercises 1x/day and a heavy load eccentric exercise 2x/day. RESULTS: After treatment, isometric strength had significantly increased in all directions, and SPADI score had significantly decreased. The TT + ET group showed a 15% higher gain in abduction strength at 90° of scapular abduction. Chi-square tests showed patients' self-rated perception of improvement was similar in both groups. CONCLUSION: Adding heavy load eccentric training resulted in a higher gain in isometric strength at 90° of scapular abduction, but was not superior for decreasing pain and improving shoulder function. This study showed that the combination of a limited amount of physiotherapy sessions combined with a daily home exercise programme is highly effective in patients with impingement. LEVEL OF EVIDENCE: II.

Electromyographic analysis of an eccentric calf muscle exercise in persons with and without Achilles tendinopathy.

OBJECTIVES: To compare surface electromyographic (EMG) activity of the gastrocnemius and soleus muscles between persons with and without Achilles tendinopathy (AT) during an eccentric muscle exercise in different knee joint positions. DESIGN: Repeated measures design. SETTING: Research laboratory. PARTICIPANTS: Participants (n = 18) diagnosed with AT and 18 control subjects were recruited. MAIN OUTCOME MEASURES: Gastrocnemius and soleus muscle activity was examined by surface (EMG) during extended and flexed knee joint conditions while performing the eccentric training technique. The EMG data were expressed as a percentage of a maximum voluntary contraction (MVC). RESULTS: EMG activity was notably higher (mean difference: 10%, effect size: 0.59) in those subjects with AT. Irrespective of the presence of AT, there was a significant interaction effect between muscle and joint position. The gastrocnemius muscle was significantly more active in the extended knee condition and soleus muscle activity was unchanged across joint positions. CONCLUSIONS: The results indicated that the presence of AT influenced calf muscle activity levels during performance of the eccentric exercise. There were differences in muscle activity during the extended and flexed knee conditions. This result does support performing Alfredson, Pietila, Jonsson, and Lorentzon (1998) eccentric exercise in an extended knee position but the specific effects of the knee flexed position on the Achilles tendon during eccentric exercise have yet to be determined, particularly in those with AT.

What predicts functional outcome after treatment for patellofemoral pain?

PURPOSE: Although physical therapy is known to be effective in treating patellofemoral pain (PFP), there is considerable individual variation in the treatment response. It is unclear why some patients benefit from a specific treatment while others do not experience improvement. This study, using a prospective study design, aims to identify factors that could predict the short-term functional outcome and account for the variation frequently seen in the outcome after conservative treatment of PFP. METHODS: Thirty-six patients (20 female and 16 male with a mean age of 23.8 ± 6.7 yr) followed a physical therapy rehabilitation program of 7 wk. Before this treatment, all patients were evaluated on subjective symptoms (pain on visual analog scales in millimeters) and functional performance (step test expressed as highest level, single-legged hop test in centimeters, and triple-hop test in centimeters). The concentric and eccentric knee extensor strength at 60°.s(-1) and 240°.s(-1) (N.m) were measured as well as the quadriceps muscle size by calculating the cross-sectional area (cm(2)) with magnetic resonance imaging. The success of the treatment was evaluated by the functional Kujala anterior knee pain scale. A linear regression model was used to identify predisposing factors for the functional outcome. RESULTS: The total quadriceps cross-sectional area (P = 0.010), the eccentric average peak torque at 60°.s(-1) (P = 0.015), and the frequency of pain at baseline (P = 0.012) have been indicated as predisposing variables in the short-term functional outcome after a physical therapy rehabilitation program for PFP (adjusted R(2) = 0.46). CONCLUSION: Patients with a greater quadriceps muscle size, lower eccentric knee strength, and less pain have a better short-term functional outcome after conservative treatment for PFP.

Muscle-tendon tissue properties in the hypermobility type of Ehlers-Danlos syndrome.

OBJECTIVE: To investigate the passive properties of the plantar flexors muscle-tendon tissue in patients with the hypermobility type of Ehlers-Danlos syndrome (EDS-HT). METHODS: Twenty-five women with EDS-HT and 25 sex- and age-matched healthy control subjects participated in the study. Passive resistive torque (PRT) of the plantar flexors was measured with an isokinetic dynamometer during 2 standardized stretch protocols to obtain the passive muscle tension. Protocol 1 consisted of 4 continuous cycles to a predetermined angle of 10° dorsiflexion. Protocol 2 consisted of a slow stretch to the onset of pain. Torque, angle, and electromyography were simultaneously recorded during the tests. To take muscle thickness into account, muscle cross-sectional area (MCSA) was obtained with peripheral quantitative computed tomography. Stiffness of the Achilles tendon was assessed using a dynamometer in combination with ultrasonography. RESULTS: The results demonstrate a significantly larger maximal joint angle in the EDS-HT patients accompanied by a similar PRT compared to the control subjects (protocol 2), indicating a lower passive muscle tension in the patient group. PRT for the predetermined angle (protocol 1) was the same for both groups and there was no difference in MSCA. Furthermore, a significantly lower Achilles tendon stiffness was seen in the patient group than in the control group. CONCLUSION: This study is the first to provide evidence for altered passive properties of the muscle-tendon unit in EDS-HT patients. These changes are thought to be associated with structural modifications in connective tissue.

Intrinsic gait-related risk factors for Achilles tendinopathy in novice runners: a prospective study.

The purpose of this prospective cohort study was to identify dynamic gait-related risk factors for Achilles tendinopathy (AT) in a population of novice runners. Prior to a 10-week running program, force distribution patterns underneath the feet of 129 subjects were registered using a footscan pressure plate while the subjects jogged barefoot at a comfortable self-selected pace. Throughout the program 10 subjects sustained Achilles tendinopathy of which three reported bilateral complaints. Sixty-six subjects were excluded from the statistical analysis. Therefore the statistical analysis was performed on the remaining sample of 63 subjects. Logistic regression analysis revealed a significant decrease in the total posterior-anterior displacement of the Centre Of Force (COF) (P=0.015) and a laterally directed force distribution underneath the forefoot at 'forefoot flat' (P=0.016) as intrinsic gait-related risk factors for Achilles tendinopathy in novice runners. These results suggest that, in contrast to the frequently described functional hyperpronation following a more inverted touchdown, a lateral foot roll-over following heel strike and diminished forward force transfer underneath the foot should be considered in the prevention of Achilles tendinopathy.

Effect of eccentric training on the plantar flexor muscle-tendon tissue properties.

PURPOSE: It has been shown that eccentric training can be effective in the rehabilitation of patients with Achilles tendonopathy. The mechanism behind these results is not clear. However, there is evidence that tendons are able to respond to repeated forces by altering their structure and composition, and, thus, their mechanical properties change. In this regard, the objective of the present study was to investigate whether eccentric training affects the mechanical properties of the plantar flexor's muscle-tendon tissue properties. METHODS: Seventy-four healthy subjects were randomized into two groups: an eccentric training group and a control group. The eccentric training group performed a 6-wk eccentric training program for the calf muscles. Before and after this period, all subjects were evaluated for dorsiflexion range of motion using universal goniometry, passive resistive torque of the plantar flexors, and stiffness of the Achilles tendon. Passive resistive torque was measured during ankle dorsiflexion on an isokinetic dynamometer. Stiffness of the Achilles tendon was assessed using a dynamometer, in combination with ultrasonography. RESULTS: The results of the study reveal that the dorsiflexion range of motion was significantly increased only in the eccentric training group. The eccentric heel drop program also resulted in a significant decrease of the passive resistive torque of the plantar flexors (from 16.423 +/- 0.827 to 12.651 +/- 0.617 N.m). The stiffness of the Achilles tendon did not change significantly as a result of training. CONCLUSION: These findings provide evidence that an eccentric training program results in changes to some of the mechanical properties of the plantar flexor muscles. These changes were thought to be associated with modifications to structure rather than to stretch tolerance.

The effect of increasing resistance on trunk muscle activity during extension and flexion exercises on training devices.

Although progressive resistance training of trunk muscles on devices is very common, today, the effects of increasing resistance on trunk muscle activity during dynamic extension and flexion movements on training devices have not been reported yet. Thirty healthy subjects participated in maximal isometric and submaximal dynamic (at 30%, 50% and 70% of maximum mean torque (MMT)) extension and flexion exercises on Tergumed lumbar training devices. The normalized (as a percentage of maximal voluntary isometric contractions (MVIC)) electromyographic activity of 16 abdominal and back muscles was investigated. The results of the present study indicated that in general, with increasing resistance from 30% MMT to 50% MMT and 70% MMT, the activity of all back muscles during the extension exercises and the activity of all abdominal muscles during the flexion exercises increased significantly. To train strength (>60% of MVIC), low intensities (30% and 50% MMT) appeared sufficient to affect the back muscles, but for the abdominals higher resistance (70% MMT) was required. In contrast to the other back muscles, the lumbar multifidus demonstrated high activity levels during both the extension and the flexion exercises. As the lumbar multifidus is demonstrated to be an important muscle in segmental stabilization of the lumbar spine, this finding may help in understanding the efficacy of rehabilitation programs using specific training devices.

Effect of static and ballistic stretching on the muscle-tendon tissue properties.

PURPOSE: Many studies have been undertaken to define the effects of static and ballistic stretching. However, most researchers have focused their attention on joint range-of-motion measures. The objective of the present study was to investigate whether static- and ballistic-stretching programs had different effects on passive resistive torque measured during isokinetic passive motion of the ankle joint and tendon stiffness measured by ultrasound imaging. METHODS: Eighty-one healthy subjects were randomized into three groups: a static-stretch group, a ballistic-stretch group, and a control group. Both stretching groups performed a 6-wk stretching program for the calf muscles. Before and after this period, all subjects were evaluated for ankle range of motion, passive resistive torque of the plantar flexors, and the stiffness of the Achilles tendon. RESULTS: The results of the study reveal that the dorsiflexion range of motion was increased significantly in all groups. Static stretching resulted in a significant decrease of the passive resistive torque, but there was no change in Achilles tendon stiffness. In contrast, ballistic stretching had no significant effect on the passive resistive torque of the plantar flexors. However, a significant decrease in stiffness of the Achilles tendon was observed in the ballistic-stretch group. CONCLUSION: These findings provide evidence that static and ballistic stretching have different effects on passive resistive torque and tendon stiffness, and both types of stretching should be considered for training and rehabilitation programs.

The influence of specific training on trunk muscle recruitment patterns in healthy subjects during stabilization exercises.

Low back pain is a major problem involving high medical costs, therefore effective prevention strategies are essential. Stabilization exercises seem to facilitate the neuromuscular control of the lumbar spine and may be useful in prevention programs. To investigate whether specific lumbar stabilization training has an effect on muscle recruitment patterns in a healthy population, in the present study 30 subjects were recruited to perform two types of testing exercises, i.e. bridging exercises and exercises in four-point kneeling, both before and after training. Surface electromyographic data of different abdominal and back muscles were obtained. After training, analysis of the relative muscle activity levels (percentage of maximal voluntary isometric contraction) showed a higher activity of the local (segmental-stabilizing) abdominal muscles, but not of the local back muscles; minimal changes in global (torque-producing) muscle activity also occurred. Analysis of the local/global relative muscle activity ratios revealed higher ratios during all exercises after training, although not all differences were significant. These results indicate that muscle recruitment patterns can be changed in healthy subjects by means of a training program that focuses on neuromuscular control. Additional studies are needed to evaluate this type of training as a prevention strategy.

Electromyographic activity of trunk and hip muscles during stabilization exercises in four-point kneeling in healthy volunteers.

Stabilization exercises are intended to optimize function of the muscles that are believed to govern trunk stability. Debate exists whether certain muscles are more important than others in optimally performing these exercises. Thirty healthy volunteers were asked to perform three frequently prescribed stabilization exercises in four-point kneeling. The electromyographic activity of different trunk and hip muscles was evaluated. Average amplitudes obtained during the exercises were normalized to the amplitude in maximal voluntary contraction (% MVIC). During all three exercises, the highest relative muscle activity levels (> 20% MVIC) were consistently found in the ipsilateral lumbar multifidus and gluteus maximus. During both the single leg extension (exercise 1) and the leg and arm extension exercise (exercise 2) the contralateral internal oblique and ipsilateral external oblique reached high levels (> 20%MVIC). During exercise 2 there were also high relative activity levels of the ipsilateral lumbar part and the contralateral thoracic part of the iliocostalis lumborum and the contralateral lumbar multifidus. During the leg and arm extension exercise with contralateral hip flexion (exercise 3) there were high relative muscle activity levels of all back muscles, except for the latissimus dorsi muscle. The lowest relative muscle activity levels (< 10% MVIC) were found in the rectus abdominis and the ipsilateral internal oblique during all exercises, and in the contralateral gluteus maximus during exercises 1 and 2. The results of this study show that in exercises in four-point kneeling performed by healthy subjects, hip and trunk muscles seem to work together in a harmonious way. This shows that when relative activity of muscles is measured, both "global and local" muscles function together in order to stabilize the spine.

Improving strength and postural control in young skiers: whole-body vibration versus equivalent resistance training.

CONTEXT: Several groups have undertaken studies to evaluate the physiologic effects of whole-body vibration (WBV). However, the value of WBV in a training program remains unknown. OBJECTIVE: To investigate whether a WBV program results in a better strength and postural control performance than an equivalent exercise program performed without vibration. DESIGN: Randomized, controlled trial. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-three Belgian competitive skiers (ages = 9-15 years). INTERVENTION(S): Subjects were assigned to either the WBV group or the equivalent resistance (ER) group for 6 weeks of training at 3 times per week. MAIN OUTCOME MEASURE(S): Isokinetic plantar and dorsiflexion peak torque, isokinetic knee flexion and extension peak torque, explosive strength (high box test), and postural control were assessed before and after the training period. RESULTS: Both training programs significantly improved isokinetic ankle and knee muscle strength and explosive strength. Moreover, the increases in explosive strength and in plantar-flexor strength at low speed were significantly higher in the WBV group than in the ER group after 6 weeks. However, neither WBV training nor ER training seemed to have an effect on postural control. CONCLUSIONS: A strength training program that includes WBV appears to have additive effects in young skiers compared with an equivalent program that does not include WBV. Therefore, our findings support the hypothesis that WBV training may be a beneficial supplementary training technique in strength programs for young athletes.

Trunk muscle activity in healthy subjects during bridging stabilization exercises.

BACKGROUND: Trunk bridging exercises are often used as therapeutic exercises for lumbopelvic stabilization. These exercises focus on the retraining of muscle coordination patterns in which optimal ratios between local segmental stabilizing and global torque producing muscle activity are assumed to be essential. However, a description of such ratios is lacking. The purpose of this study was to investigate both relative (as a percentage of maximal voluntary isometric contraction) muscle activity levels and ratios of local to global muscle activity, during bridging stabilization exercises. METHODS: Thirty healthy university students (15 men, 15 women) with a mean age of 19.6 year volunteered to perform 3 bridging exercises (single bridging, ball bridge and unilateral bridging). The surface electromyographic activity of different trunk muscles was evaluated on both sides. RESULTS: During all bridging exercises, the ratio of the internal oblique to the rectus abdominis was very high due to minimal relative activity of the rectus abdominis. In general, the ratio of the internal/external abdominal oblique activity was about 1. However, during the unilateral bridging exercise, the ipsilateral internal/external abdominal oblique activity ratio was 2.79 as a consequence of the significant higher relative activity of the internal oblique compared to the external oblique. The relative muscle activity and the ratios of the back muscles demonstrated similar activity levels for all back muscles, resulting in ratios about 1. CONCLUSION: Both the minimal relative activity of the rectus abdominis and the high internal oblique to the rectus abdominis activity ratio reported in the present study are in accordance with results of other trunk stabilization exercises. The relative muscle activity and the ratio of the abdominal obliques seem to alter depending on the task and the presumable need for stability. The findings concerning the relative muscle activity and the ratios of the back muscles support the assumption that during these bridging exercises, all back muscles contribute in a similar way to control spine positions and movements in a healthy population.

Reliability of a functional clinical test battery evaluating postural control, proprioception and trunk muscle activity.

OBJECTIVE: The purpose of this study was to examine the repeatability and reproducibility of the different tests of a clinical test battery evaluating the components of functional spinal stability: postural control (sway velocity data), proprioception (repositioning error), and muscle activation (electromyographic data). DESIGN: A total of 28 healthy volunteers participated in this study: 14 in the repeatability study and 14 in the reproducibility study. Each subject was tested three times, with an interval of 1 wk between the test sessions. The intraclass correlation coefficients and the standard error of the measurements as a percentage of the grand mean were calculated. RESULTS: The intraclass correlation coefficients for both the repeatability and the reproducibility evaluation showed good to excellent reliability for all variables (intraclass correlation coefficient, 0.60-0.98). The standard error of the measurements as a percentage of the grand mean ranged from 0.004 to 19.94. CONCLUSIONS: The functional clinical test battery investigated in this study proved to be a reliable tool in the assessment of healthy subjects. The evaluation of postural control, proprioception, and muscle activity (coordination, stabilization, maximal voluntary isometric contraction, endurance, and flexion-relaxation) showed good to excellent repeatability and reproducibility. Further analysis of the reliability of these variables in a clinical setting, particularly in patients with low back pain, seems appropriate.

Intrinsic risk factors for the development of achilles tendon overuse injury: a prospective study.

BACKGROUND: Although Achilles tendon overuse injuries occur commonly, our understanding of the pathologic changes and the factors that predispose athletes to them is limited. PURPOSE: To identify measurable intrinsic risk factors for Achilles tendon overuse injuries. STUDY DESIGN: Cohort study (prognosis); Level of evidence, 2. METHODS: Sixty-nine male officer cadets followed the same 6-week basic military training. Before this training, each subject was evaluated for anthropometrical characteristics, isokinetic ankle muscle strength, ankle joint range of motion, Achilles tendon stiffness, explosive strength, and leisure and sports activity. During military training, Achilles tendon overuse injuries were registered and diagnosed by the same medical doctor. To identify the intrinsic risk factors, a multivariate analysis with the use of stepwise logistic regression was performed. The sensitivity, specificity, and cutoff values of the risk factors were evaluated by receiver operating characteristic curve analysis. RESULTS: Ten of the 69 male recruits (14.5%) sustained an Achilles tendon overuse injury diagnosed on the basis of medical history and clinical examination. Analysis revealed that male recruits with lower plantar flexor strength and increased dorsiflexion excursion were at a greater risk of Achilles tendon overuse injury. The cutoff value of the plantar flexor strength at 85% sensitivity was 50.0 N.m, with a 4.5% specificity; the cutoff value of the dorsiflexion range of motion at 85% sensitivity was 9.0 degrees , with 24.2% specificity. CONCLUSIONS: The strength of the plantar flexors and amount of dorsiflexion excursion were identified as significant predictors of an Achilles tendon overuse injury. A plantar flexor strength lower than 50.0 N.m and dorsiflexion range of motion higher than 9.0 degrees were possible thresholds for developing an Achilles tendon overuse injury.

Isokinetic Scapular Muscle Performance in Overhead Athletes With and Without Impingement Symptoms.

Context: Overhead activities such as throwing, tennis, or volleyball place athletes at considerable risk for overuse injuries. A relationship between scapulothoracic muscle imbalance and shoulder pain has been suggested.Objective: To compare the isokinetic muscle performance of the scapular muscles between overhead athletes with impingement symptoms and uninjured overhead athletes and to identify strength deficits in the patient population.Design: A repeated-measures analysis of variance with 1 within-subjects factor (side) and 1 between-subjects factor (group) was used to compare strength values and agonist:antagonist ratios across sides and across groups.Setting: University laboratory.Patients or Other Participants: Thirty overhead athletes with chronic shoulder impingement symptoms and 30 overhead athletes without a history of shoulder pain.Intervention(s): A linear protraction-retraction movement in the scapular plane at 2 velocities (12.2 cm/s and 36.6 cm/s).Main Outcome Measure(s): Isokinetic strength values and protraction:retraction ratios for both velocities.Results: Overhead athletes with impingement symptoms showed decreased force output:body weight at both velocities in the protractor muscles on the injured side compared with the uninjured side (-13.7% at slow velocity, -15.5% at high velocity) and compared with the control group at high velocity (-20.7%). On both sides, the patient group had significantly lower protraction:retraction ratios than the control group, measured at slow velocity (nondominant = -11%, dominant = -13.7%).Conclusions: Overhead athletes with impingement symptoms demonstrated strength deficits and muscular imbalance in the scapular muscles compared with uninjured athletes.

Intrinsic risk factors for inversion ankle sprains in male subjects: a prospective study.

BACKGROUND: Many variables have been retrospectively associated with ankle sprains. However, very little is known about factors predisposing people to these injuries. HYPOTHESIS: Measurable intrinsic factors might predispose male athletes to ankle sprains. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: A total of 241 male physical education students were evaluated for possible intrinsic risk factors for inversion sprains at the beginning of their academic study. The evaluated intrinsic risk factors included anthropometrical characteristics, functional motor performances, ankle joint position sense, isokinetic ankle muscle strength, lower leg alignment characteristics, postural control, and muscle reaction time during a sudden inversion perturbation. Subjects were followed prospectively for 1 to 3 years. RESULTS: A total of 44 (18%) of the 241 male subjects sustained an inversion sprain; 4 sprained both ankles. Cox regression analysis revealed that male subjects with slower running speed, less cardiorespiratory endurance, less balance, decreased dorsiflexion muscle strength, decreased dorsiflexion range of motion, less coordination, and faster reaction of the tibialis anterior and gastrocnemius muscles are at greater risk of ankle sprains. CONCLUSION: Based on our findings, it is suggested that running speed, cardiorespiratory endurance, balance, dorsiflexion strength, coordination, muscle reaction, and dorsiflexion range of motion at the ankle are associated with the risk of ankle inversion sprains in male subjects.

Stretching and injury prevention: an obscure relationship.

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.