Simon S. Yeung

A prospective cohort study of hamstring injuries in competitive sprinters: preseason muscle imbalance as a possible risk factor

Background: Hamstring injuries are common in sprinters. Identifying preseason risk factors is essential to target injury-prone athletes and develop injury preventive measures. Objective: To investigate the incidence of hamstring muscle injury in sprinters over an athletic season and to explore the preseason predictor of this injury. Design: Prospective cohort study. Participants: 44 sprinters from the Hong Kong Sports Institute, the Hong Kong Amateur Athletic Association and intercollegiate athletic teams were recruited. Methods: Preseason assessment of hamstring flexibility, concentric and eccentric isokinetic peak torque and peak torque angle were obtained at the beginning of an athletic season. The athletes were followed over 12 months and were asked to report all injuries resulting from training and competition. Results: Eight athletes sustained hamstring injuries over the season. The injury rate was 0.87 per 1000 h of exposure. The incidence of injuries was higher at the beginning of the season, with 58.3% injuries occurring in the first 100 h of exposure. Cox regression analysis revealed that athletes with a decrease in the hamstring : quadriceps peak torque ratio of less than 0.60 at an angular velocity of 180°/s have a 17-fold increased risk of hamstring injury. Conclusion: Performing preseason hamstring : quadriceps peak torque ratio assessments may be useful to identify sprinters susceptible to hamstring injury.

What are the Main Running-Related Musculoskeletal Injuries?

BackgroundMusculoskeletal injuries occur frequently in runners and despite many studies about running injuries conducted over the past decades it is not clear in the literature what are the main running-related musculoskeletal injuries (RRMIs).ObjectiveThe aim of this study is to systematically review studies on the incidence and prevalence of the main specific RRMIs.MethodsAn electronic database search was conducted using EMBASE (1947 to October 2011), MEDLINE (1966 to October 2011), SPORTDiscus™ (1975 to October 2011), the Latin American and Caribbean Center on Health Sciences Information (LILACS) [1982 to October 2011] and the Scientific Electronic Library Online (SciELO) [1998 to October 2011] with no limits of date or language of publication. Articles that described the incidence or prevalence rates of RRMIs were considered eligible. Studies that reported only the type of injury, anatomical region or incomplete data that precluded interpretation of the incidence or prevalence rates of RRMIs were excluded. We extracted data regarding bibliometric characteristics, study design, description of the population of runners, RRMI definition, how the data of RRMIs were collected and the name of each RRMI with their rates of incidence or prevalence. Separate analysis for ultra-marathoners was performed. Among 2924 potentially eligible titles, eight studies (pooled n = 3500 runners) were considered eligible for the review. In general, the articles had moderate risk of bias and only one fulfilled less than half of the quality criteria established.ResultsA total of 28 RRMIs were found and the main general RRMIs were medial tibial stress syndrome (incidence ranging from 13.6% to 20.0%; prevalence of 9.5%), Achilles tendinopathy (incidence ranging from 9.1% to 10.9%; prevalence ranging from 6.2% to 9.5%) and plantar fasciitis (incidence ranging from 4.5% to 10.0%; prevalence ranging from 5.2% to 17.5%). The main ultra-marathon RRMIs were Achilles tendinopathy (prevalence ranging from 2.0% to 18.5%) and patellofemoral syndrome (prevalence ranging from 7.4% to 15.6%).ConclusionThis systematic review provides evidence that medial tibia stress syndrome, Achilles tendinopathy and plantar fasciitis were the main general RRMIs, while Achilles tendinopathy and patellofemoral syndrome were the most common RRMIs for runners who participated in ultra-marathon races.

A systematic review of interventions to prevent lower limb soft tissue running injuries

Objectives—To assess the available evidence for preventive strategies for lower limb soft tissue injuries caused by running. Methods—An electronic database search was conducted using The Cochrane Musculoskeletal Injuries Group Specialised Register, The Cochrane Controlled Trials Register, Medline, Embase, Sport Discus, Heracles, Atlantes, Biosis, Cinahl, Scisearch, Current Contents, Index To Theses and Dissertation Abstracts. Any randomised or quasi-randomised trials evaluating interventions to prevent running injuries to lower limb soft tissue were included. The eligibility of trials for inclusion and the quality of the trials were independently assessed by two reviewers. Results—Exposure to a high training load (duration, frequency, or running distance) increases the risk of injury, and thus modification of the training schedule can reduce the incidence of injury. The effectiveness of stretching exercises and of insoles in the prevention of lower extremity soft tissue injuries caused by running is not known. Wearing a knee brace with a patellar support ring may be effective in the prevention of anterior knee pain caused by running. Conclusions—This review provides evidence for the effectiveness of the modification of training schedules in reducing lower limb soft tissue running injuries. More studies are required to quantify the optimal training loads and to confirm that knee braces can prevent knee pain. It is important to note that the studies included in this review had few female participants therefore the results may not be generalisable.

Role of the calcium-calpain pathway in cytoskeletal damage after eccentric contractions

The mechanism(s) underlying eccentric damage to skeletal muscle cytoskeleton remain unclear. We examined the role of Ca(2+) influx and subsequent calpain activation in eccentric damage to cytoskeletal proteins. Eccentric muscle damage was induced by stretching isolated mouse muscles by 20% of the optimal length in a series of 10 tetani. Muscle force and immunostaining of the cytoskeletal proteins desmin, dystrophin, and titin were measured at 5, 15, 30, and 60 min after eccentric contractions and compared with the control group that was subjected to 10 isometric contractions. A Ca(2+)-free solution and leupeptin (100 microM), a calpain inhibitor, were applied to explore the role of Ca(2+) and calpain, respectively, in eccentric muscle damage. After eccentric contractions, decreases in desmin and dystrophin immunostaining were apparent after 5 min that accelerated over the next 60 min. Increased titin immunostaining, thought to indicate damage to titin, was evident 10 min after stretch, and fibronectin entry, indicating membrane disruption, was evident 20 min after stretch. These markers of damage also increased in a time-dependent manner. Muscle force was reduced immediately after stretch and continued to fall, reaching 56 +/- 2% after 60 min. Reducing extracellular calcium to zero or applying leupeptin minimized the changes in immunostaining of cytoskeletal proteins, reduced membrane disruption, and improved the tetanic force. These results suggest that the cytoskeletal damage and membrane disruption were mediated primarily by increased Ca(2+) influx into muscle cells and subsequent activation of calpain.

Effects of fatigue on the temporal neuromuscular control of vastus medialis muscle in humans.

Abstract The effects of muscle fatigue on the temporal neuromuscular control of the vastus medialis (VM) muscle were investigated in 19 young male subjects. The electromyogram (EMG) activities of VM and the force generation capacities of the quadriceps muscle were monitored before and after a fatigue protocol. In response to light signals, which were triggered randomly, the subjects made three maximal isometric knee extensions. This was then followed by the fatigue protocol which consisted of 30 isometric maximal voluntary contractions at a sequence of 5-s on and 5-s off. Immediately after the exercise to fatigue, the subjects performed another three maximal isometric contractions in response to the light signals. The effects of fatigue on the temporal neuromuscular control were then investigated by dividing the total reaction time (TRT) into premotor time (PMT) and electromechanical delay (EMD). The TRT was defined as the time interval between the light signal and the onset of the knee extension force. The PMT was defined as the time from the light signal to the onset of EMG activities of VM, and EMD as the time interval between onset of EMG activities to that of force generation. Following the contractions to fatigue there was a significant decrease in peak force (Fpeak, P = 0.016), an increase in the root mean square (rms)-EMG: Fpeak quotient (P = 0.001) but an insignificant change in the median frequency (P = 0.062) and rms-EMG (P = 0.119). Significant lengthening of mean EMD was found after the fatigue protocol [0.0396 (SD 0.009) vs 0.0518 (SD 0.016) s P < 0.001]. The lengthening of EMD in VM would affect the stabilizing effect of the patella during knee extension. The faster mean PMT [0.2445 (SD 0.093) vs 0.2075 (SD 0.074) s, P = 0.042] following the fatigue protocol might have compensated for the lengthened EMD and contributed to the insignificant change in the mean TRT [0.284 (SD 0.09) vs 0.259 (SD 0.073) s, P = 0.164]. This was probably related to the low level of fatigue (15% decrease in force) and the stereotyped nature of the action such that the effects of the fatigue on neuromuscular control were likely to have been attributable to peripheral processes.

Electrical Stimulation Influences Satellite Cell Proliferation and Apoptosis in Unloading-Induced Muscle Atrophy in Mice

Muscle atrophy caused by disuse is accompanied by adverse physiological and functional consequences. Satellite cells are the primary source of skeletal muscle regeneration. Satellite cell dysfunction, as a result of impaired proliferative potential and/or increased apoptosis, is thought to be one of the causes contributing to the decreased muscle regeneration capacity in atrophy. We have previously shown that electrical stimulation improved satellite cell dysfunction. Here we test whether electrical stimulation can also enhance satellite cell proliferative potential as well as suppress apoptotic cell death in disuse-induced muscle atrophy. Eight-week-old male BALB/c mice were subjected to a 14-day hindlimb unloading procedure. During that period, one limb (HU-ES) received electrical stimulation (frequency: 20 Hz; duration: 3 h, twice daily) while the contralateral limb served as control (HU). Immunohistochemistry and western blotting techniques were used to characterize specific proteins in cell proliferation and apoptosis. The HU-ES soleus muscles showed significant improvement in muscle mass, cross-sectional area, and peak tetanic force relative to the HU limb (p<0.05). The satellite cell proliferative activity as detected within the BrdU+/Pax7+ population was significantly higher (p<0.05). The apoptotic myonuclei (detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) and the apoptotic satellite cells (detected by cleaved Poly [ADP-ribose] polymerase co-labeled with Pax7) were reduced (p<0.05) in the HU-ES limb. Furthermore the apoptosis-inducing factor and cleaved caspase-3 were down-regulated while the anti-apoptotic Bcl-2 protein was up-regulated (p<0.05), in the HU-ES limb. These findings suggest that the electrical stimulation paradigm provides an effective stimulus to rescue the loss of myonuclei and satellite cells in disuse muscle atrophy, thus maintaining a viable satellite cell pool for subsequent muscle regeneration. Optimization of stimulation parameters may enhance the outcome of the intervention.

Cumulative spinal loading exposure methods for manual material handling tasks. Part 1: is cumulative spinal loading associated with lower back disorders?

Objective: To critically appraise the observational studies linking cumulative spinal loading and lower back disorders (LBD) among workers engaged in manual material handling and to explore the association between cumulative spinal loading and LBD through a meta-analysis of papers reported in the published literature. Background: Although studies have indicated a definitive relationship between long-term exposure to manual materials handling and LBD, little is generally known about the validity of the cumulative exposure assessment methods used for predicting the risk of LBD. Methods: A comprehensive electronic search on the subject was conducted. The articles found from the search were critically appraised from an epidemiological standpoint. The strengths and weaknesses of the studies were documented. A quantitative assessment was performed for the meta-analysis estimate using the fixed-effect and random-effects (Dersimonian and Laird method) models. The assessments were conducted in two ways: with a standard approach that does not consider study quality and with a modified method that allows weighting scores to be calculated based on the rating of the quality of each study. Results: The electronic search resulted in identification of four epidemiological papers, three of which provided sufficient information for an assessment of epidemiological quality and two of which provided sufficient data to conduct a meta-analysis. The results showed that the methodological quality of the studies ranged from poor to marginal. Without considering the overall study quality for the exposure data, (1) there were substantial differences between the three studies that were rated for epidemiological quality as evidenced by the significant heterogeneity testing at the 10% level and (2) the difference in the mean exposure values between the study and control groups (i.e. summary mean difference) was significant at the 5% level for both the fixed-effect and random-effects models. After accounting for overall study quality, the heterogeneity was reduced but still significant at the 10% level and the summary mean difference was greater than that without the quality score. The meta-odds ratio for LBD outcomes was 1.66 (95% confidence interval using quality scores = 1.46–1.89). Conclusions: The preliminary findings suggest that there likely is an association between cumulative spinal loading and LBD. Further, there are considerable differences among the studies in terms of exposure assessment techniques. A subsequent paper (Part II of this research) provides an in-depth analysis of cumulative spinal loading exposure methods and discusses critical issues related to their reliability and validity for estimating force distribution and practicality for field measurement.

Effects of knee joint angles and fatigue on the neuromuscular control of vastus medialis oblique and vastus lateralis muscle in humans.

Abstract The effects of different knee joint angles and fatigue on the neuromuscular control of the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles were investigated in 17 (11 men, 6 women) young subjects. The electromyogram (EMG) activities and the force generation capacities were monitored before and after a fatigue protocol at three different knee joint angles, 90°, 150°, 175° of knee extension, on three occasions. In response to randomly triggered light signals, the subjects performed three isometric maximal voluntary contraction (IMVC) that lasted for 4 to 8 s. This was then followed by the fatigue protocol which consisted of six bursts of contractions fixed at 30 s on and 10 s off. Immediately after the exercise to fatigue, the subjects performed another three IMVC in response to the light signals. Repeated measures ANOVA were performed to examine the effects of fatigue at these three positions on the electromechanical delay (EMD), median frequency (fmed), peak force (Fpeak) and root mean square (rms)-EMG:Fpeak quotient of VMO and VL. The results revealed a significant effect of the three knee joint angles on the EMD before the fatigue (P < 0.05). The fatigue protocol induced a significant decrease in Fpeak at all the three positions (P < 0.01). However, the fatigue induced a significant decrease of fmed at only 90° and 150° of knee extension (P < 0.01). This occurred in parallel with the lengthening of EMD at these two joint angles (P < 0.01 and P < 0.05). The effects of fatigue on the fmed and EMD were not significant between VMO and VL at all three angles. The insignificant difference in fmed and EMD between VMO and VL at the three knee positions before and after fatigue indicated that no preferential onset activation between VMO and VL had occurred.

The association between back pain and trunk posture of workers in a special school for the severe handicaps

BackgroundThe present study aims to determine the time spent in different static trunk postures during a typical working day of workers in a special school for the severe handicaps.MethodsEighteen workers with low back pain (LBP) and fifteen asymptomatic workers were recruited. A cross-sectional design was employed to study the time spent in different static trunk postures which was recorded by a biaxial accelerometer attached to the T12 level of the back of the subjects.ResultsThe results of ANCOVA revealed that subjects with LBP spent significantly longer percentage of time in static trunk posture when compared to normal (p < 0.05). It was also shown that they spent significantly longer time in trunk flexion for more than 10° (p < 0.0125).ConclusionAn innovative method has been developed for continuous tracking of spinal posture, and this has potential for widespread applications in the workplace. The findings of the present investigation suggest that teachers in special schools are at increased risk of getting LBP. In order to minimise such risk, frequent postural change and awareness of work posture are recommended.

Cumulative spinal loading exposure methods for manual material handling tasks. Part 2: methodological issues and applicability for use in epidemiological studies

Objective: The goal of this paper is to review and discuss methodological issues related to cumulative spinal loading exposure assessment methods. Background: Research has indicated that there likely is an association between integrated spinal loading and lower back pain. A number of studies have been conducted to evaluate cumulative load; however, comparisons between studies is difficult due to the use of different methods for the assessment of cumulative spinal loading. Methods: A comprehensive electronic search was conducted to locate articles dealing with methods of cumulative spinal loading estimation. The articles were evaluated with respect to methods for obtaining postural data, methods for estimating spinal loads, methods for integrating loads over time and spinal load parameters to be measured. Results: Thirteen articles were located. A summary of the methods used to estimate cumulative spinal load is described and evaluated. Conclusions: There is a pressing need for integrated spinal loading methods that are reliable, valid and practical for use in large occupational epidemiological studies. A number of research needs were outlined aimed at improving the ability to use cumulative load to predict risk of low back disorders due to manual material handling.