Individual distribution of muscle hypertrophy among hamstring muscle heads: Adding muscle volume where you need is not so simple.

PURPOSE: The aim of this study was to determine whether a 9-week resistance training program based on high load (HL) versus low load combined with blood flow restriction (LL-BFR) induced a similar (i) distribution of muscle hypertrophy among hamstring heads (semimembranosus, SM; semitendinosus, ST; and biceps femoris long head, BF) and (ii) magnitude of tendon hypertrophy of ST, using a parallel randomized controlled trial. METHODS: A total of 45 participants were randomly allocated to one of three groups: HL, LL-BFR, and control (CON). Both HL and LL-BFR performed a 9-week resistance training program composed of seated leg curl and stiff-leg deadlift exercises. Freehand 3D ultrasound was used to assess the changes in muscle and tendon volume. RESULTS: The increase in ST volume was greater in HL (26.5 ± 25.5%) compared to CON (p = 0.004). No difference was found between CON and LL-BFR for the ST muscle volume (p = 0.627). The change in SM muscle volume was greater for LL-BFR (21.6 ± 27.8%) compared to CON (p = 0.025). No difference was found between HL and CON for the SM muscle volume (p = 0.178).There was no change in BF muscle volume in LL-BFR (14.0 ± 16.5%; p = 0.436) compared to CON group. No difference was found between HL and CON for the BF muscle volume (p = 1.0). Regarding ST tendon volume, we did not report an effect of training regimens (p = 0.411). CONCLUSION: These results provide evidence that the HL program induced a selective hypertrophy of the ST while LL-BFR induced hypertrophy of SM. The magnitude of the selective hypertrophy observed within each group varied greatly between individuals. This finding suggests that it is very difficult to early determine the location of the hypertrophy among a muscle group.

Development of a prediction model to determine responders to conservative treatment in people with symptomatic hand osteoarthritis: A secondary analysis of a single-centre, randomised feasibility trial.

BACKGROUND: Conservative treatments are beneficial for people with hand osteoarthritis (OA). OBJECTIVE: It was the purpose of this study to develop and internally validate both a basic model and a more complex model that could predict responders to conservative treatments in people with hand OA. DESIGN: This was a secondary analysis of a single-centre, randomised feasibility study. METHODS: Fifty-nine participants (34 responders) with hand osteoarthritis were recruited from the general population. Participants were randomised to receive either advice alone, or advice in combination with blood flow restriction training (BFRT), or traditional high intensity training (HIT). Participants underwent supervised hand exercises three times per week for six weeks. The OMERACT-OARSI criteria were utilised to determine responders vs non responders to treatment at the end of six weeks. A basic logistic regression model (treatment type, expectations, adherence) and a more complex logistic regression model (basic model variables plus pain catastrophising and neuropathic pain features) were created. Discrimination ability, and calibration were assessed. Internal model validation through bootstrapping (200 repetitions) was utilised to calculate the prediction model optimism. RESULTS: The results showed that the basic model presented with acceptable discrimination (optimism corrected c-statistic: 0.72, 95% CI 0.71-0.73) and calibration (slope = 1.41; intercept = 0.68). The more complex model had better discrimination but poorer calibration. CONCLUSION: A prediction tool was created to provide an individualised estimate of treatment response in people with hand OA. Future studies will need to validate this model in other groups of patients. TRIAL REGISTRATION: https://www.anzctr.org.au/- ACTRN12617001270303.

Neglect-like symptoms and their relationships with other clinical features in people with hand osteoarthritis: An exploratory study.

BACKGROUND: Symptomatic hand osteoarthritis (OA) is a debilitating condition. Body schema impairments such as neglect-like symptoms have been previously reported in people with symptomatic hand OA, however, little is known about their clinical importance, or relationships with other clinical features. OBJECTIVES: The aim of this cross-sectional study was to assess the prevalence of neglect-like symptoms in painful hand OA and their association with measures of depression, pain catastrophising, sleep quality, function, pain interference and pain duration whilst controlling for important covariates. DESIGN: Secondary analysis of cross-sectional study. METHODS: Logistic regression with age, sex, and worst pain intensity as covariates were utilised to assess differences between participants with and without neglect-like symptoms. RESULTS: A total of 121 participants were recruited. Sixty-one percent of participants presented with neglect-like symptoms. Participants with longer pain duration had greater odds of presenting with neglect-like symptoms (OR: 1.10 95%CI: 1.01 to 1.19; p = 0.012). No difference was observed for depression, pain catastrophising, sleep quality, function, or pain interference. CONCLUSIONS: A large proportion of participants with symptomatic hand OA reported neglect-like symptoms, the presence of which was associated with longer pain duration.

Factors associated with persistent opioid use 6-12 months after primary total knee arthroplasty.

Persistent pain following knee arthroplasty occurs in up to 20% of patients and may require ongoing analgesia, including extended opioid administration. A comprehensive secondary analysis was performed from results of a study that considered persistent postoperative pain in 242 patients who underwent unilateral knee arthroplasty using a standardised enhanced recovery programme. Opioid prescribing for 12 months before and 12 months after surgery was evaluated and converted to oral morphine equivalents. Demographic, functional, psychological and pain questionnaires were completed along with quantitative sensory testing and genetic analysis. Forty-nine percent of patients had at least one opioid prescription in the 12 months before surgery. Opioid prescriptions were filled in 93% of patients from discharge to 3 months and in 27% of patients ≥6 months after surgery. Persistent opioid use ≥6 months after surgery was strongly associated with pre-operative opioid use (RR 3.2, p < 0.001 (95%CI 1.9-5.4)). The median (IQR [range]) oral morphine equivalent daily dose was 3.6 (0.9-10.5 [0-100.0]) mg pre-operatively, 35.0 (22.5-52.5 [4.6-180.0]) mg in hospital, 12.8 (5.1-24.8 [0-57.9]) mg from discharge to 3 months and 5.9 (4.5-12.0 [0-44.5]) mg at ≥6 months following surgery. Predictors of increased daily oral morphine equivalent ≥6 months after surgery included increased average daily oral morphine equivalent dose compared with previous values (lag), increased body mass index and three or more comorbid pain sites. Persistent opioid use was not associated with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain (RR 1.003, p = 0.655, 95%CI 0.65-1.002) or WOMAC function (RR 1.001, p = 0.99, 95%CI 0.99-1.03) outcomes 6 months after surgery. There was no association between persistent opioid use and pre-operative quantitative sensory testing results or psychological distress. Pre-operatively, patients with a higher body mass index, more comorbid pain sites and those who had filled an opioid prescription in the last 12 months, were at increased risk of persistent opioid use and a higher oral morphine equivalent daily dose ≥ 6 months after surgery. Strategies need to be developed to limit dose and duration of persistent opioid use in patients following knee arthroplasty surgery.

Six weeks of resistance training (plus advice) vs advice only in hand osteoarthritis: A single-blind, randomised, controlled feasibility trial.

BACKGROUND: People with hand osteoarthritis (OA) may benefit from resistance training interventions. To date the feasibility of a such interventions for symptomatic hand OA, as per international guidelines, is unknown. OBJECTIVE: Determine the feasibility of a clinical trial comparing resistance training to an advice only control group in people with symptomatic hand OA. DESIGN: Single-blind, randomised, controlled feasibility study. METHODS: The American College of Rheumatology criteria for hand OA were utilised for inclusion. Participants were randomly allocated (1:1:1) to advice and blood flow restriction training (BFRT), advice and traditional high intensity training (HIT), or advice only (control). Participants receiving BFRT and HIT underwent supervised hand exercises three times a week for six weeks. Feasibility measures included recruitment rate, adherence, exercise induced pain, training acceptability, pain flares, and adverse events. Number of treatment responders, pain, grip strength, and hand function were also recorded. RESULTS: In total, 191 participants were screened, 59 (31%) were included. Retention rate was 89% for BFRT and 79% for HIT. Exercise did not worsen pain following training sessions, and training acceptability was equal between groups. Pain flares occurred in 1.6% (BFRT) and 4% (HIT) out of all the training sessions. There was one adverse event in the HIT group, with the participants withdrawing from the study due to pain. The number of treatment responders, and improvements in pain, were greater with BFRT and HIT. Grip and function did not improve. CONCLUSION: A clinical trial comparing resistance training to advice for people with symptomatic hand OA is feasible.

Steroids to reduce the impact on delirium (STRIDE): a double-blind, randomised, placebo-controlled feasibility trial of pre-operative dexamethasone in people with hip fracture.

Neuro-inflammation may be important in the pathogenesis of postoperative delirium following hip fracture surgery. Studies have suggested a potential role for steroids in reducing postoperative delirium; however, the potential efficacy and safety of pre-operative high-dose dexamethasone in this specific population is largely unknown. Conducting such a study could be challenging, considering the multidisciplinary team involvement and the emergency nature of the surgery. The aim of this study was to assess feasibility and effectiveness of dexamethasone given as early as possible following hospital admission for hip fracture, to inform whether a full-scale trial is warranted. This single-centre, randomised, double-blind, placebo-controlled study randomly allocated 79 participants undergoing hip fracture surgery to dexamethasone 20 mg or placebo pre-operatively. Eligibility and recruitment rates, timing of the intervention and adverse events were recorded. Incidence and severity of postoperative delirium were assessed using the 4AT delirium screening tool and the Memorial Delirium Assessment Scale. Postoperative pain, length of stay and mortality were also assessed. The eligibility rate for inclusion was 178/527 (34%), and 57/178 (32%) of eligible patients presented to hospital when no researcher was available (e.g. after-hours, weekends, public holidays). Recruitment was limited mainly by ethical limitations (not including patients with impaired cognition) and lack of weekend staffing. Median (IQR [range]) time from emergency department admission to drug administration was 13.3 (5.9-17.6 [1.8-139.6]) hours. There was a significant difference in delirium severity scores, favouring the dexamethasone group: median (IQR [range]) 5 (3-6 [3-7]) vs. 9 (6-13 [5-14]) in the placebo group, with the probability of superiority effect size being 0.89, p = 0.010. Delirium incidence did not differ between groups: 6/40 (15%) in the dexamethasone group vs. 9/39 (23%) in the placebo group, relative risk (95%CI) 0.65 (0.22-1.65), p = 0.360). A larger randomised controlled trial is feasible and ideally this should include people with existing cognitive impairment, seven days-a-week cover and a multicentre design.

Persistent postoperative pain after total knee arthroplasty: a prospective cohort study of potential risk factors.

BACKGROUND: Persistent postoperative pain (PPP) is common after total knee arthroplasty (TKA). The primary aim of this prospective cohort study was to identify important predictors of moderate to severe PPP 6 and 12 months after TKA. METHODS: Consenting patients (n=300) undergoing primary unilateral TKA attended a preoperative session to collect clinical information (age, gender, BMI, preoperative knee pain, comorbid pain, likely neuropathic pain) and psychological variables (depression, anxiety, catastrophising, expected pain). Quantitative sensory testing (pressure pain thresholds, temporal summation, conditioned pain modulation) was performed, and blood samples were obtained for subsequent genotyping of OPRM1 and COMT. Acute postoperative pain was measured at rest and during movement. Surgical factors (surgery time, patella resurfacing, anaesthetic type) were collected after operation. Follow-up questionnaires were sent 6 and 12 months after surgery. Multivariate logistic regression was used to identify predictors of PPP. RESULTS: The prevalence of moderate to severe PPP was 21% (n=60) and 16% (n=45) 6 and 12 months after surgery, with 55% (n=33) and 60% (n=31) of PPP likely neuropathic in nature. At 6 months, a combination of preoperative pain intensity, expected pain, trait anxiety, and temporal summation (Akaike information criterion, 309.9; area under receiver operating characteristic (ROC) curve, 0.70) was able to correctly classify 66% of patients into moderate to severe PPP and no to mild PPP groups. At 12 months, preoperative pain intensity, expected pain, and trait anxiety (Akaike information criterion, 286.8; area under ROC curve, 0.66) correctly classified 66% of patients. CONCLUSIONS: Findings from this study highlight several factors that may be targeted in future intervention studies to reduce the development of PPP. TRIAL REGISTRY NUMBER: ACTRN12612001089820.

Transcranial direct current stimulation for upper limb neuropathic pain: A double-blind randomized controlled trial.

BACKGROUND: While promising, there are mixed findings for the efficacy of transcranial direct current stimulation (tDCS) for the management of chronic pain. The goal of this study was to evaluate the effect of anodal tDCS on pain and function in people with upper limb neuropathic pain. METHODS: The study was a double-blinded, randomized controlled trial. Thirty participants were randomly allocated into active and sham tDCS groups. Baseline assessments of pain and function, as well as quantitative sensory testing (QST) to probe the function of the nociceptive system, were undertaken prior to participants receiving 5 days of active or sham anodal tDCS (1 mA) over the primary motor cortex. The outcome measures were re-assessed 1, 3 and 8 weeks following the intervention. RESULTS: Group analyses revealed no significant improvement in pain, function, or QST measures over time in either group. However, there were significantly more individual responders (≥30% change in pain) in the active compared to the sham tDCS group at the final follow-up. In the active group, there was a significant correlation indicating those with higher baseline pain had greater pain relief. CONCLUSIONS: On group analyses, no evidence was provided that 1 mA tDCS is beneficial for people with upper limb neuropathic pain, although it may provide lasting pain relief for some individuals. SIGNIFICANCE: At the group level, we found no evidence that 5 days of active 1 mA tDCS is effective for people with upper limb neuropathic pain. However, there were more individual responders in the active tDCS group compared to sham, and those who responded early after treatment experienced sustained pain relief.

TENS Alleviates Muscle Weakness Attributable to Attenuation of Ia Afferents.

Quadriceps weakness is a notable problem following knee damage. Research has shown effectiveness of TENS in improving Quadriceps weakness associated with arthrogenic muscle inhibition. However, these studies were not focused upon short term delivery of TENS, nor did they examine the potential mechanism(s). The present study examined the effect of 25-30 s of TENS upon weakness induced temporarily by a prolonged vibration. Subjects performed eccentric MVCs under 2 conditions (TENS and no-TENS). First, MVC was measured at baseline. For the TENS condition, TENS was applied to each subject's knee joint during a second MVC measurement after vibration. For no-TENS condition, TENS was not applied during the 2nd MVC measurement. MVC between pre-and post-vibration stimulation were compared across the 2 conditions. The results showed that MVC and EMG of TENS-condition was larger than that of no-TENS condition. Our results suggest that TENS could partially restore α-motoneuron activation, despite the induced dysfunctional γ-loop. These results suggest that mechanisms independent of the γ-loop such as a direct facilitation of the QF α-motoneuron pool by a long latency spinal-reflex and/or supraspinal mechanisms appear more likely to be responsible. The findings provide further support for utilizing TENS, even when γ-loop dysfunction is present following joint damage.

Effects of hip and head position on ankle range of motion, ankle passive torque, and passive gastrocnemius tension.

Ankle joint range of motion (ROM) is notably influenced by the position of the hip joint. However, this result remains unexplained. Thus, the aim of this study was to test if the ankle passive torque and gastrocnemius muscle tension are affected by the hip and the head positions. The torque and the muscle shear elastic modulus (measured by elastography to estimate muscle tension) were collected in nine participants during passive ankle dorsiflexions performed in four conditions (by combining hip flexion at 90 or 150°, and head flexed or neutral). Ankle maximum dorsiflexion angle significantly decreased by flexing the hip from 150 to 90° (P < 0.001; mean difference 17.7 ± 2.5°), but no effect of the head position was observed (P > 0.05). Maximal passive torque and shear elastic modulus were higher with the hip flexed at 90° (P < 0.001). During submaximal ROM, no effects of the head and hip positioning (P > 0.05) were found for both torque and shear elastic modulus at a given common ankle angle among conditions. Shifts in maximal ankle angle due to hip angle manipulation are not related neither to changes in passive torque nor tension of the gastrocnemius. Further studies should be addressed to better understand the functional role of peripheral nerves and fasciae in the ankle ROM limits.

Predictors of persistent pain after total knee arthroplasty: a systematic review and meta-analysis.

BACKGROUND: Several studies have identified clinical, psychosocial, patient characteristic, and perioperative variables that are associated with persistent postsurgical pain; however, the relative effect of these variables has yet to be quantified. The aim of the study was to provide a systematic review and meta-analysis of predictor variables associated with persistent pain after total knee arthroplasty (TKA). METHODS: Included studies were required to measure predictor variables prior to or at the time of surgery, include a pain outcome measure at least 3 months post-TKA, and include a statistical analysis of the effect of the predictor variable(s) on the outcome measure. Counts were undertaken of the number of times each predictor was analysed and the number of times it was found to have a significant relationship with persistent pain. Separate meta-analyses were performed to determine the effect size of each predictor on persistent pain. Outcomes from studies implementing uni- and multivariable statistical models were analysed separately. RESULTS: Thirty-two studies involving almost 30 000 patients were included in the review. Preoperative pain was the predictor that most commonly demonstrated a significant relationship with persistent pain across uni- and multivariable analyses. In the meta-analyses of data from univariate models, the largest effect sizes were found for: other pain sites, catastrophizing, and depression. For data from multivariate models, significant effects were evident for: catastrophizing, preoperative pain, mental health, and comorbidities. CONCLUSIONS: Catastrophizing, mental health, preoperative knee pain, and pain at other sites are the strongest independent predictors of persistent pain after TKA.

From adverse drug event detection to prevention. A novel clinical decision support framework for medication safety.

BACKGROUND: Errors related to medication seriously affect patient safety and the quality of healthcare. It has been widely argued that various types of such errors may be prevented by introducing Clinical Decision Support Systems (CDSSs) at the point of care. OBJECTIVES: Although significant research has been conducted in the field, still medication safety is a crucial issue, while few research outcomes are mature enough to be considered for use in actual clinical settings. In this paper, we present a clinical decision support framework targeting medication safety with major focus on adverse drug event (ADE) prevention. METHODS: The novelty of the framework lies in its design that approaches the problem holistically, i.e., starting from knowledge discovery to provide reliable numbers about ADEs per hospital or medical unit to describe their consequences and probable causes, and next employing the acquired knowledge for decision support services development and deployment. Major design features of the framework's services are: a) their adaptation to the context of care (i.e. patient characteristics, place of care, and significance of ADEs), and b) their straightforward integration in the healthcare information technologies (IT) infrastructure thanks to the adoption of a service-oriented architecture (SOA) and relevant standards. RESULTS: Our results illustrate the successful interoperability of the framework with two commercially available IT products, i.e., a Computerized Physician Order Entry (CPOE) and an Electronic Health Record (EHR) system, respectively, along with a Web prototype that is independent of existing healthcare IT products. The conducted clinical validation with domain experts and test cases illustrates that the impact of the framework is expected to be major, with respect to patient safety, and towards introducing the CDSS functionality in practical use. CONCLUSIONS: This study illustrates an important potential for the applicability of the presented framework in delivering contextualized decision support services at the point of care and for making a substantial contribution towards ADE prevention. Nonetheless, further research is required in order to quantitatively and thoroughly assess its impact in medication safety.

Level versus inclined walking: ambulatory compensations in children with cerebral palsy under outdoor conditions.

PURPOSE: To investigate how children with cerebral palsy (CP) adapt their gait to inclined outdoor walking conditions. METHODS: Ten children with CP, Gross Motor Function System level II, and 10 children with typical development participated. Walking velocity, stride length and ankle, knee, hip, and trunk sagittal plane angles were calculated for 4 conditions: indoor walkway, outdoor walkway, and walking up and down a 7° inclined ramp. RESULTS: Gait patterns were unchanged between indoor and outdoor level walking. During up-slope walking, both groups increased hip and knee flexion at foot strike to accommodate the slope. During down-slope walking, both groups increased knee flexion in midstance to lower the body down the slope. Children with CP had greater forward trunk lean (P < .005) during up-slope walking and greater posterior trunk lean during down-slope walking (P < .0001). CONCLUSION: Children with CP adapt to inclined walking conditions similarly to peers but use greater postural adaptations.

Functional adaptation of knee cartilage in asymptomatic female novice runners compared to sedentary controls. A longitudinal analysis using delayed Gadolinium Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC).

OBJECTIVE: To longitudinally estimate the change in glycosaminoglycan content of knee cartilage in asymptomatic untrained female novice runners participating in a Start To Run program (STR) compared to sedentary controls. METHOD: Nine females enrolling in a 10-week STR and 10 sedentary controls participated voluntarily. Prior to and after the 10-week period, both groups were subjected to dGEMRIC imaging. dGEMRIC indices of knee cartilage were determined at baseline and for the change after the 10-week period in both groups. Based on a self-reported weekly log, physical activity change during the study was depicted as decreased, unchanged or increased. The Mann-Whitney U and Kruskal-Wallis tests were applied to test the hypotheses that dGEMRIC changes occurred between groups and according to physical activity changes respectively. RESULTS: No significant differences were established between groups for dGEMRIC indices at baseline (P=0.541). A significant positive change of the median dGEMRIC index in the runners group was demonstrated when compared to the controls [+11.66ms (95% CI: -25.29, 44.43) vs -9.56ms (95% CI: -29.55, 5.83), P=0.006]. The change in dGEMRIC index differed significantly according to physical activity change (P=0.014), showing an increase in dGEMRIC index with increasing physical activity. CONCLUSION: Since cartilage appears to positively respond to moderate running when compared to a sedentary lifestyle, this running scheme might be considered a valuable tool in osteoarthritis prevention strategies. Caution is warranted when applying these results to a wider population and to longer training periods.

Improvements to Hoang et al.'s method for measuring passive length-tension properties of human gastrocnemius muscle in vivo.

While the passive mechanical properties of a musculo-articular complex can be determined using the relationship between the articular angle and the passive torque developed in resistance to motion, the properties of different structures of the musculo-articular complex cannot be easily assessed. Recently, an elegant method has been proposed to estimate the passive length-tension properties of gastrocnemius muscle-tendon unit (Hoang et al., 2005). In the present paper, two improvements of this method are proposed to decrease the number of parameters required to assess the passive length-tension relationship from 9 to 2. Furthermore, these two parameters have physical meaning as they represent a passive muscle-tendon stiffness index (alpha) and the muscle-tendon slack length (l(0)). alpha and l(0) are relevant clinical parameters to study the chronic effects of aging, training protocols or neuromuscular pathologies on the passive mechanical properties of the muscle-tendon unit. Eight healthy subjects performed passive loading/unloading cycles at 5 degrees /s with knee angle at 6 knee angles to assess the torque-angle relationships and to apply the modified method. Numerical optimization was used to minimize the squared error between the experimental and the modeled relationships. The experiment was performed twice to assess the reliability of alpha and l(0) across days. The results showed that the reliability of the two parameters was good (alpha: ICC=0.82, SEM=6.1m(-1), CV=6.3% and l(0): ICC=0.83, SEM=0.29 cm, CV=0.9%). Using a sensitivity analysis, it was shown that the numerical solution was unique. Overall, the findings may provide increased interest in the method proposed by Hoang et al. (2005).

Static and cyclic stretching: their different effects on the passive torque-angle curve.

The findings of previous research indicate that the passive torque-angle curve may be different according to whether individuals have undertaken cyclic or static stretching. To date, no authors have compared these curves in the same subjects. We hypothesised that static stretching would lead to a constant change in range of motion across torque levels with the shape of the curve being unchanged, while cyclic stretching would change the shape of the curve. To test this hypothesis, eight subjects performed five passive knee extension/flexion cycles on a Biodex dynamometer at 5 degrees s(-1) to 80% of their maximal range of motion before and after a static stretching protocol. The difference in angle between pre and post stretching torque-angle curves was calculated at 11 levels of torque from 0% to 100% of the maximal torque with a 10% increment. The mean change in angle across these 11 torque levels was then calculated. The findings showed that after static stretching a relatively constant mean change of 5.2 degrees was noted across torque levels. In contrast, after cyclic stretching the angle change depended upon the torque level with greater change observed toward the start of the range of motion. The findings indicated that different mechanisms were operating depending upon the type of stretching procedure performed. Changes in muscle resting length and thixotropy were thought to be responsible.

The short-term effects of running on the deformation of knee articular cartilage and its relationship to biomechanical loads at the knee.

OBJECTIVE: To investigate the short-term effects of recreational running on the deformation of knee articular cartilage and to examine the relationship between changes in knee cartilage volume and biomechanical modulators of knee joint load. METHOD: Twenty healthy volunteers participated in a two phase cross-sectional study. Session 1 involved Magnetic Resonance Imaging (MRI) of femoral and tibial cartilage volumes prior to and following a 30 min period of relaxed sitting, which was directly followed by a recreational run of 5000 steps. Subsequently, all participants undertook a laboratory study of their running gait to compare biomechanical derived measures of knee joint loading with changes in cartilage volume. Estimates of knee joint load were determined using a rigid-link segment, dynamic biomechanical model of the lower limbs and a simplified muscle model. RESULTS: Running resulted in significant deformation of the medial (5.3%, P<0.01) and lateral femoral cartilage (4.0%, P<0.05) and lateral aspect of the tibial cartilage (5.7%, P<0.01), with no significant differences between genders. Maximum compression stress was significantly correlated with percentage changes in lateral femoral cartilage volume (r(2)=0.456, P<0.05). No other biomechanical variables correlated with volume changes. CONCLUSION: Limited evidence was found linking biomechanical measures of knee joint loading and observed short-term deformation of knee articular cartilage volume following running. Further enhancement of knee muscle modelling and analysis of stress distribution across cartilage are needed if we are to fully understand the contribution of biomechanical factors to knee joint loading and the pathogenesis of knee osteoarthritis (OA).

The effect of angular velocity and cycle on the dissipative properties of the knee during passive cyclic stretching: a matter of viscosity or solid friction.

BACKGROUND: The mechanisms behind changes in mechanical parameters following stretching are not understood clearly. This study assessed the effects of joint angular velocity on the immediate changes in passive musculo-articular properties induced by cyclic stretching allowing an appreciation of viscosity and friction, and their contribution to changes in torque that occur. METHODS: Ten healthy subjects performed five passive knee extension/flexion cycles on a Biodex dynamometer at five preset angular velocities (5-120 deg/s). The passive torque and knee angle were measured, and the potential elastic energy stored during the loading and the dissipation coefficient were calculated. FINDINGS: As the stretching velocity increased, so did stored elastic energy and the dissipation coefficient. The slope of the linear relationship between the dissipation coefficient and the angular velocity was unchanged across repetitions indicating that viscosity was unlikely to be affected. A difference in the y-intercept across repetitions 1 and 5 was indicative of a change in processes associated with solid friction. Electromyographical responses to stretching were low across all joint angular velocities. INTERPRETATION: Torque changes during cyclic motion may primarily involve solid friction which is more indicative of rearrangement/slipping of collagen fibers rather than the redistribution of fluid and its constituents within the muscle. The findings also suggest that it is better to stretch slowly initially to reduce the amount of energy absorption required by tissues, but thereafter higher stretching speeds can be undertaken.