Di J. Newham

Sensorimotor changes and functional performance in patients with knee osteoarthritis

OBJECTIVE Muscles are essential components of our sensorimotor system that help maintain balance and perform a smooth gait, but it is unclear whether arthritic damage adversely affects muscle sensorimotor function. Quadriceps sensorimotor function in patients with knee osteoarthritis (OA) was investigated, and whether these changes were associated with impairment of functional performance. METHODS Quadriceps strength, voluntary activation, and proprioceptive acuity (joint position sense acuity) were assessed in 103 patients with knee OA and compared with 25 healthy control subjects. In addition, their postural stability, objective functional performance (the aggregate time for four activities of daily living), and disabilities (Lequesne index) were also investigated. RESULTS Compared with the control subjects, the patients with knee OA had weaker quadriceps (differences between group mean 100N, CI 136, 63N), poorer voluntary activation (20% CI 13, 25%) that was associated with quadriceps weakness, and impaired acuity of knee joint position sense (1.28°, CI 0.84, 1.73°). As a group the patients were more unstable (p=0.0017), disabled (10, CI 7, 11), and had poorer functional performance (19.6 seconds, CI 14.3, 24.9 seconds). The most important predictors of disability were objective functional performance and quadriceps strength. CONCLUSIONS In patients with knee OA, articular damage may reduce quadriceps motoneurone excitability, which decreases voluntary quadriceps activation thus contributing to quadriceps weakness, and diminishes proprioceptive acuity. The arthrogenic impairment in quadriceps sensorimotor function and decreased postural stability was associated with reduced functional performance of the patients.

Muscle activity and acceleration during whole body vibration: Effect of frequency and amplitude

BACKGROUND Whole body vibration may improve muscle and bone strength, power and balance although contradictory findings have been reported. Prolonged exposure may result in adverse effects. We investigated the effects of high (5.5 mm) and low (2.5mm) amplitude whole body vibration at various frequencies (5-30 Hz) on muscle activity and acceleration throughout the body. METHODS Surface electromyographic activity was recorded from 6 leg muscles in 12 healthy adults (aged 31.3 (SD 12.4) years). The average rectified acceleration of the toe, ankle, knee, hip and head was recorded from 15 healthy adults (36 (SD 12.1) years) using 3D motion analysis. FINDINGS Whole body vibration increased muscle activity 5-50% of maximal voluntary contraction with the greatest increase in the lower leg. Activity was greater with high amplitude at all frequencies, however this was not always significant (P<0.05-0.001). Activation tended to increase linearly with frequency in all muscles except gluteus maximus and biceps femoris. Accelerations throughout the body ranged from approximately 0.2 to 9 g and decreased with distance from the platform. Acceleration at the head was always < 0.33 g. The greatest acceleration of the knee and hip occurred at approximately 15 Hz and thereafter decreased with increasing frequency. INTERPRETATION Above the knee at frequencies > 15 Hz acceleration decreased with distance from the platform. This was associated with increased muscle activity, presumably due to postural control and muscle tuning mechanisms. The minimal acceleration at the head reduces the likelihood of adverse reactions. The levels of activation are unlikely to cause hypertrophy in young healthy individuals but may be sufficient in weak and frail people.

Effects of whole body vibration on motor unit recruitment and threshold

Whole body vibration (WBV) has been suggested to elicit reflex muscle contractions but this has never been verified. We recorded from 32 single motor units (MU) in the vastus lateralis of 7 healthy subjects (34 ± 15.4 yr) during five 1-min bouts of WBV (30 Hz, 3 mm peak to peak), and the vibration waveform was also recorded. Recruitment thresholds were recorded from 38 MUs before and after WBV. The phase angle distribution of all MUs during WBV was nonuniform (P < 0.001) and displayed a prominent peak phase angle of firing. There was a strong linear relationship (r = -0.68, P < 0.001) between the change in recruitment threshold after WBV and average recruitment threshold; the lowest threshold MUs increased recruitment threshold (P = 0.008) while reductions were observed in the higher threshold units (P = 0.031). We investigated one possible cause of changed thresholds. Presynaptic inhibition in the soleus was measured in 8 healthy subjects (29 ± 4.6 yr). A total of 30 H-reflexes (stimulation intensity 30% Mmax) were recorded before and after WBV: 15 conditioned by prior stimulation (60 ms) of the antagonist and 15 unconditioned. There were no significant changes in the relationship between the conditioned and unconditioned responses. The consistent phase angle at which each MU fired during WBV indicates the presence of reflex muscle activity similar to the tonic vibration reflex. The varying response in high- and low-threshold MUs may be due to the different contributions of the mono- and polysynaptic pathways but not presynaptic inhibition.

Long-term intensive electrically stimulated cycling by spinal cord-injured people: effect on muscle properties and their relation to power output.

Inactivity and muscular adaptations following spinal cord injury (SCI) result in secondary complications such as cardiovascular disease, obesity, and pressure sores. Functional electrically stimulated (FES) cycling can potentially reduce these complications, but previous studies have provided inconsistent results. We studied the effect of intensive long‐term FES cycle training on muscle properties in 11 SCI subjects (mean ± SEM: 41.8 ± 2.3 years) who had trained for up to 1 hour/day, 5 days/week, for 1 year. Comparative measurements were made in 10 able‐bodied (AB) subjects. Quadriceps maximal electrically stimulated torque increased fivefold (n = 5), but remained lower than in AB individuals. Relative force response at 1 HZ decreased, relaxation rate remained unchanged, and fatigue resistance improved significantly. Power output (PO) improved to a lesser extent than quadriceps torque and not to a greater extent than has been reported previously. We need to understand the factors that limit PO in order to maximize the benefits of FES cycling. Muscle Nerve 38: 1304–1311, 2008

The metabolic costs of different types of contractile activity of the human adductor pollicis muscle.

1. The metabolic costs and physiological consequences of shortening contractions of a human muscle working in situ have been compared with those of the muscle maintaining a continuous isometric contraction and when performing repeated brief isometric contractions. 2. After a total of 10 s stimulation, the shortening and intermittent brief isometric protocols had very similar effects, causing a 30% loss of force and a threefold increase in the half‐time of relaxation. This was in contrast to the continuous isometric contraction protocol where there was less than 10% loss of force or slowing of relaxation. 3. The ATP cost over the first 5 s of the continuous isometric protocol was 27 mmol (l intracellular water)‐1 while for the shortening and repeated brief isometric protocols the costs were 48 and 46 mmol (l intracellular water)‐1, respectively. 4. The results show that shortening and repeated brief isometric contractions are considerably more energetically demanding, and hence more fatiguing, than sustained isometric contractions.

Whole-body vibration in addition to strength and balance exercise for falls-related functional mobility of frail older adults: a single-blind randomized controlled trial

Objectives: To investigate the effects of whole-body vibration in addition to an exercise programme on functional mobility and related outcomes for frail older fallers. Design: Single-blind randomized parallel group trial. Setting: UK; National Health Service assessment and rehabilitation facility for older people. Participants: Frail older fallers: 38 (80 ± 8.6 years) performed the exercise with whole-body vibration (vibration group), and 39 (82 ± 8.1 years) without (exercise group). Intervention: Sixty minutes supervised exercise class three times weekly for eight weeks ± whole-body vibration (up to 5 × 1 minute, 15–30 Hz and 2–8 mm peak-to-peak). Measurements: Timed Up and Go, 6-m walk, static balance, fear of falling (FES-I) and self-reported health status (SF-12 version 2) were assessed at baseline, four weeks (mobility measures only), eight weeks and six months. Results: Timed Up and Go and 6-m walk improved in both groups at eight weeks (P < 0.01), but significantly more in the vibration group (timed up and go: 38 vs. 20%, P < 0.05); 6-m walk: (36 vs. 18.1%, P < 0.05, respectively). Balance, fear of falling and physical component of the self-reported health status improved similarly in both groups (P < 0.05). At follow-up, no significant differences from baseline remained for any measure. The mean total time experienced was 37% of maximal target. Conclusion: The addition of whole-body vibration to strength and balance exercise resulted in greater improvements in functional mobility than exercise alone, despite achieving lower than anticipated exposure. Gains from neither intervention were sustained at six months.

Chronic exertional compartment syndrome : muscle changes with isometric exercise

UNLABELLED Chronic exertional compartment syndrome (CECS) is a well-documented cause of lower leg pain in active individuals. The pathophysiology is unclear, although it is generally believed to be associated with increased intramuscular pressure, but there is very little information about muscle function in relation to the onset of pain. PURPOSE To investigate strength, fatigue, and recovery of the anterior tibial muscles in CECS patients and healthy subjects during an isometric exercise protocol. METHODS Twenty patients and 22 control subjects (mean age 27.6 yr and 33.0 yr, respectively) performed a 20-min isometric exercise protocol consisting of intermittent maximal voluntary contractions (MVC). Central fatigue was evaluated by comparing changes in electrically stimulated (2 s at 50 Hz) and voluntary contraction force before and during the exercise, and then throughout 10 min of recovery. Muscle size was measured by ultrasonography. Pain and cardiovascular parameters were also examined. RESULTS The absolute MVC forces were similar, but MVC:body mass of the patients was lower (P < 0.05) as was the ratio of MVC to muscle cross-sectional area (P < 0.01). The extent of central and peripheral fatigue was similar in the two groups. The patients reported significantly higher levels of pain during exercise (P < 0.05 at 4 min) and after the first minute of recovery (P < 0.001). An 8% increase in muscle size after exercise was observed for both groups. There were no differences in the cardiovascular responses of the two groups. CONCLUSIONS CECS patients were somewhat weaker than normal but fatigued at a similar rate during isometric exercise. Patients reported higher pain than controls despite comparable changes in muscle size, suggesting that abnormally tight fascia are not the main cause of CECS symptoms.

The human force:velocity relationship; activity in the knee flexor and extensor muscles before and after eccentric practice.

Abstract The human voluntary force:velocity relationship frequently fails to demonstrate the expected high eccentric forces. Possible explanations include unique activation strategies which might be affected by neural learning mechanisms. We investigated the effect of practicing eccentric contractions on (1) the force: velocity relationship of the human knee extensor muscles and (2) the extent of agonist and antagonist muscle activity. Eight healthy adults [seven women, group mean age 31 (SEM 5) years ± ] practised twice a week for 4 weeks using their non-dominant legs. Each session comprised three isokinetic concentric and eccentric maximal voluntary contractions (MVC) at randomised angular velocities of 100, 200 and 300° · s−1. Before and after, the force:velocity relationship was determined bilaterally (angular velocities 0–300° · s−1). There were no significant differences in the forces generated or relative electromyogram (EMG) activity after practice, although there was a trend for dynamic forces to increase. Beforehand, the bilateral eccentric MVC forces were lower than isometric (P < 0.0025); afterwards they were broadly similar. The agonist EMG was similar during isometric and eccentric contractions, but lower during concentric (P < 0.03). Antagonist EMG activity showed considerable individual variation, was similar during all contraction types and tended to be greater during dynamic contractions. These data indicate that neither central learning mechanisms nor total muscle activation strategies underlie the human failure to produce the expected high eccentric voluntary forces in humans.

Inter-rater reliability of postural observation after stroke

Objective: To explore the inter-observer reliability of bedside observations of stroke patients’ posture using two versions of a pictorial tool. Design: Three projects were conducted. The initial version of the tool was used in project 1. The modified version was used in projects 2 and 3. In each project a pair of observers (comprising the main observer and one of five co-observers with varying degrees of experience in observing posture) used the tool to make simultaneous observations of 19 aspects of the posture of a sample of stroke patients. Each patient was observed in one or more of four positions (seated, supine and lying on the affected and unaffected side). The degree of inter-observer agreement was sought by calculating kappa values and percentage agreement. Setting: Medical wards, care of the elderly wards and a stroke unit. Subjects: A convenience sample of 57 stroke patients. Results: Four hundred and forty paired sets of observations were made (200 in project 1, 140 in project 2 and 100 in project 3). The main observer was in every pair. The co-observers made between 50 and 135 sets of observations each. When the results from all three projects were amassed, acceptable percentage agreement (i.e. 0%) was obtained for 67% (n = 78) and 73% (n = 55) of the results collected on aspects of the posture of the affected upper and lower limbs respectively. In contrast, acceptable percentage agreement for observations relating to the head, neck and trunk was obtained for only 34% (n = 50) of the results collected. Uneven distributions in the data made kappa values difficult to interpret. Inter-observer agreement was not noticeably higher for pairs in which both observers had prior experience of observing posture after stroke than for pairs in which one observer was relatively inexperienced. Conclusions: The tool has potential as a quick and simple means of collecting information at the bedside about stroke patients’ posture. Refinements, additional training in using the tool for observers and further testing are suggested before its wider use is advocated.

Mechanism of Action of Spinal Mobilizations: A Systematic Review.

Study design. Systematic review. Objective. To review the evidence regarding the mechanism of action of mobilizations. Summary of background data. Spinal mobilizations—low velocity passive oscillatory movements—reduce spinal pain in some patient subgroups. Identifying patients likely to respond remains a challenge since mobilizations’ mechanism(s) of action are unclear. Methods. Medline, Web of Science, Cinahl, Embase, and Scopus databases were searched for relevant studies. Reference lists of included studies were hand searched. Studies were included if the intervention was passive spinal mobilizations, participants were symptomatic, and outcomes evaluated possible mechanisms of action. Methodological quality was independently assessed by two assessors using a modified Cochrane Back Review Group tool. Results. Twenty-four studies were included in the review. Four were classified high risk, 14 moderate risk, and four low risk of bias. Commonest methodological limitations were lack of participant blinding, adequate randomization and allocation concealment, and sample size calculation. Evidence suggests that spinal mobilizations cause neurophysiological effects resulting in hypoalgesia (local and/or distal to mobilization site), sympathoexcitation, and improved muscle function. Mobilizations have no effect on temperature pain threshold. Three of four studies reported reduction in spinal stiffness, heterogeneous in location and timing. There is limited evidence (one study in each case) to suggest that mobilizations produce increased nociceptive flexion reflex threshold, improved posture, decreased concentration of substance P in saliva, and improved sway index measured in cervical extension. Evidence does not support an effect on segmental vertebral movement. Two studies investigated correlations between hypoalgesia and mechanism: one found a correlation with sympathoexcitatory changes, whereas the other found no correlation with change in stiffness. Conclusion. These findings suggest involvement of an endogenous pain inhibition system mediated by the central nervous system, although this is yet to be investigated directly. There is limited evidence regarding other possible mechanisms. Level of Evidence: 3