Phu Hoang

Passive mechanical properties of human gastrocnemius muscle-tendon units, muscle fascicles and tendons in vivo

SUMMARY This study provides the first in vivo measures of the passive length–tension properties of relaxed human muscle fascicles and their tendons. A new method was used to derive passive length–tension properties of human gastrocnemius muscle–tendon units from measures of ankle stiffness obtained at a range of knee angles. Passive length–tension curves of the muscle–tendon unit were then combined with ultrasonographic measures of muscle fascicle length and pennation to determine passive length–tension curves of the muscle fascicles and tendons. Mean slack lengths of the fascicles, tendons and whole muscle–tendon units were 3.3±0.5 cm, 39.5±1.6 cm and 42.3±1.5 cm, respectively (means ± s.d., N=6). On average, the muscle–tendon units were slack (i.e. their passive tension was zero) over the shortest 2.3±1.2 cm of their range. With combined changes of knee and ankle angles, the maximal increase in length of the gastrocnemius muscle–tendon unit above slack length was 6.7±1.9 cm, of which 52.4±11.7% was due to elongation of the tendon. Muscle fascicles and tendons underwent strains of 86.4±26.8% and 9.2±4.1%, respectively, across the physiological range of lengths. We conclude that the relaxed human gastrocnemius muscle–tendon unit falls slack over about one-quarter of its in vivo length and that muscle fascicle strains are much greater than tendon strains. Nonetheless, because the tendons are much longer than the muscle fascicles, tendons contribute more than half of the total compliance of the muscle–tendon unit.

Falls in people with MS—an individual data meta-analysis from studies from Australia, Sweden, United Kingdom and the United States

Background: Falls are common in people with multiple sclerosis (PwMS). Previous studies have generally included small samples and had varied methods. Objectives: The objectives of this paper are to compile fall rates across a broad range of ages and disease severity and to definitively assess the extent to which MS-associated and demographic factors influence fall rates. Methods: Individual data from studies in four countries that prospectively measured falls for three months were analyzed. We determined fall rates, prevalence of fallers (≥1 falls) and frequent fallers (≥2 falls), location and timing of falls, and fall-related demographic factors. Results: A total of 537 participants reported 1721 falls: 56% were fallers and 37% frequent fallers. Most falls occurred indoors (65%) between 6 a.m. and 6 p.m. (75%). Primary progressive MS was associated with significantly increased odds of being a faller (odds ratio (OR) 2.02; CI 1.08–3.78). Fall risk peaked at EDSS levels of 4.0 and 6.0 with significant ORs between 5.30 (2.23–12.64) and 5.10 (2.08–12.47). The fall rate was lower in women than men (relative risk (RR) 0.80; CI 0.67–0.94) and decreased with increasing age (RR 0.97 for each year, CI 0.95–0.98). Conclusion: PwMS are at high risk of falls and there are important associations between falls and MS-associated disability, gender and age.

Falls Efficacy Scale-International: A Cross-Sectional Validation in People With Multiple Sclerosis

OBJECTIVE To evaluate psychometric properties of 16-item and 7-item Falls Efficacy Scale-International (FES-I) in people with multiple sclerosis (MS). DESIGN Validation and prospective cohort study. SETTING People with MS living in metropolitan areas. PARTICIPANTS Community-dwelling people with MS (N=169; aged 21-73y) who were referred to Multiple Sclerosis Australia for physiotherapy assessment. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES FES-I scores and a range of sociodemographic, physical, and neuropsychological measures. RESULTS The mean score for the 16-item FES-I was 34.9±11.2, and the mean score for the 7-item FES-I was 14.7±4.7. FES-I total scores were normally distributed: skewness of .35 (SEM=.19) for the 16-item and .47 (SEM .19) for the 7-item FES-I, indicating the absence of floor and ceiling effects. Internal reliability was excellent, with Cronbachs alpha values of .94 (16-item) and .86 (7-item). Rasch analyses indicated that the structure and measurement properties were better for the 7-item FES-I than for the 16-item FES-I. Construct validity of both scales was supported by sensitivity to group differences relating to demographic characteristics and fall-risk factors. CONCLUSIONS The findings indicate that both 16-item and 7-item versions of the FES-I provide valuable information about the fear of falling in people with MS. However, the 7-item version of FES-I has better psychometric properties in people with MS.

Myofascial force transmission between the human soleus and gastrocnemius muscles during passive knee motion

The plantarflexors of the lower limb are often assumed to act as independent actuators, but the validity of this assumption is the subject of considerable debate. This study aims to determine the degree to which passive changes in gastrocnemius muscle length, induced by knee motion, affect the tension in the adjacent soleus muscle. A second aim is to quantify the magnitude of myofascial passive force transmission between gastrocnemius and adjacent soleus. Fifteen healthy volunteers participated. Simultaneous ultrasound images of the gastrocnemius and soleus muscles were obtained during passive knee flexion (0-90°), while keeping the ankle angle fixed at either 70° or 115°. Image correlation analysis was used to quantify muscle fascicle lengths in both muscles. The data show that the soleus muscle fascicles elongate significantly during gastrocnemius shortening. The approximate change in passive soleus force as a result of the observed change in fascicle length was estimated and appears to be <5 N, but this estimate is sensitive to the assumed slack length of soleus.

Passive Mechanical Properties of Gastrocnemius Muscles of People With Ankle Contracture After Stroke

OBJECTIVE To investigate the mechanisms of contracture after stroke by comparing passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in people with ankle contracture after stroke with control participants. DESIGN Cross-sectional study. SETTING Laboratory in a research institution. PARTICIPANTS A convenience sample of people with ankle contracture after stroke (n=20) and able-bodied control subjects (n=30). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Stiffness and lengths of gastrocnemius muscle-tendon units, lengths of muscle fascicles, and tendons at specific tensions. RESULTS At a tension of 100N, the gastrocnemius muscle-tendon unit was significantly shorter in participants with stroke (mean, 436mm) than in able-bodied control participants (mean, 444mm; difference, 8mm; 95% confidence interval [CI], 0.2-15mm; P=.04). Muscle fascicles were also shorter in the stroke group (mean, 44mm) than in the control group (mean, 50mm; difference, 6mm; 95% CI, 1-12mm; P=.03). There were no significant differences between groups in the mean stiffness or length of the muscle-tendon units and fascicles at low tension, or in the mean length of the tendons at any tension. CONCLUSIONS People with ankle contracture after stroke have shorter gastrocnemius muscle-tendon units and muscle fascicles than control participants at high tension. This difference is not apparent at low tension.

Prevalence of joint contractures and muscle weakness in people with multiple sclerosis

Abstract Objectives: To investigate the prevalence of joint contracture (limited passive range of joint motion) and muscle weakness in a population with multiple sclerosis (MS). A secondary aim was to establish normative data of functional tests of mobility and balance of people with MS who are still ambulant. Design: Cross-sectional study. Setting: People with MS living in metropolitan Sydney, Australia. Participants: 330 people with MS living in metropolitan Sydney, Australia were randomly sampled on 23 July 2009 from the MS Australia register and invited to participate. Main outcome measures: Passive range of motion of large joints of the limbs and muscle strength. Tests of walking and balance were also conducted. Results: 156 people (109 females, 47 males; mean age 54.2 years; mean time since diagnosis 14.9 years) agreed to participate and were assessed. Fifty-six per cent (56%) of participants had contracture in at least one major joint of upper or lower limb. The most common site of contracture was the ankle (43.9%). Seventy per cent (70%) of participants had muscle weakness in one or more muscle groups. As muscle weakness, joint contractures were present at early stage of MS and the prevalence was associated with the progression of the disease. Conclusions: These data show that in addition to muscle weakness joint contractures are highly prevalent among people with MS, especially in the ankle joint. This implicates that prevention of contracture is crucial in providing rehabilitation to people with MS. Implications for Rehabilitation Joint contractures are highly prevalent of people with MS, especially in the lower limb, even at an early stage. While many interventions such as stretching and serial casting have been implemented to reduce contractures, there is not yet strong evidence for their effectiveness. Further research is required.

Are muscles mechanically independent

most physiology texts imply that the mechanism by which force is transmitted from sarcomeres to muscle insertions is simple: when skeletal muscles contract, cross-bridge forces are transmitted along myofibrils, through the sarcolemma and extracellular matrix to tendons and, ultimately, bones. At

Passive mechanical properties of the gastrocnemius after spinal cord injury

In this study we compared passive mechanical properties of gastrocnemius muscle–tendon units, muscle fascicles, and tendons in control subjects and people with ankle contractures after spinal cord injury.

Effects of a home-based step training programme on balance, stepping, cognition and functional performance in people with multiple sclerosis - a randomized controlled trial

Background: Stepping impairments increase fall risk in people with MS. No studies have evaluated step training for reducing fall risk in this population. Objectives: To determine if step training can improve physical and neuropsychological measures associated with falls in MS. Methods: 50 PwMS with moderate disability participated in a randomized controlled trial in which intervention group participants (n = 28) performed step training for 12 weeks while controls (n = 22) continued usual physical activity. The primary outcomes were choice stepping reaction time (CSRT) and Stroop stepping test (SST) time. Secondary outcomes included balance test (postural sway, CSRT components), gait speed and cognitive tests, nine-hole peg test (9-HPT) and MS functional composite (MSFC) score. Results: 44 participants completed the study and no adverse events were reported. Compared with the control group, the intervention group performed significantly better at retest in CSRT and SST times, and tests of sway with eyes open, 9-HPT, single and dual task gait speed and MSFC score. There was a non-significant trend for fewer falls in the intervention group. Conclusions: The findings indicate that the step training programme is feasible, safe and effective in improving stepping, standing balance, coordination and functional performance in people with MS.

Passive mechanical properties of gastrocnemius in people with multiple sclerosis

BACKGROUND There is evidence to suggest that contractile properties of muscles in people with multiple sclerosis change as a consequence of demyelination in central nervous system. However, passive properties of muscles in people with multiple sclerosis have not been previously investigated. The purpose of this study was to characterise passive mechanical properties of gastrocnemius in people with multiple sclerosis and to compare these properties with those of gastrocnemius in neurologically normal people. METHODS Ten people with multiple sclerosis having signs and symptoms of weakness in the legs (Disease step 1-3) and 10 age- and sex-matched healthy people participated in the study. Ultrasound images of muscle fascicles of medial gastrocnemius as well as passive ankle torque and ankle angle data were obtained simultaneously as the ankle was rotated through its full range with the knee in a range of positions. Analysis of ultrasound images and passive ankle torque-angle relations allowed us to derive the slack lengths and maximal strains of whole muscle-tendon units, muscle fascicles and tendons. Paired-samples t-tests were used to compare these variables in the two groups. RESULT There was no difference between subjects with multiple sclerosis and healthy controls in the mean slack lengths and mean maximal strains of the whole muscle-tendon units or of their fascicles or tendons. INTERPRETATIONS These data suggests that typically, in people with multiple sclerosis who have impaired lower limbs but are still ambulatory, the passive mechanical properties of the gastrocnemius muscles are normal.