Ross D. Pollock

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.

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.

An investigation into the relationship between age and physiological function in highly active older adults

The relationship between age and physiological function remains poorly defined and there are no physiological markers that can be used to reliably predict the age of an individual. This could be due to a variety of confounding genetic and lifestyle factors, and in particular to ill‐defined and low levels of physical activity. This study assessed the relationship between age and a diverse range of physiological functions in a cohort of highly active older individuals (cyclists) aged 55–79 years in whom the effects of lifestyle factors would be ameliorated. Significant associations between age and function were observed for many functions. V̇O2 max was most closely associated with age, but even here the variance in age for any given level was high, precluding the clear identification of the age of any individual. The data suggest that the relationship between human ageing and physiological function is highly individualistic and modified by inactivity.

Respiratory Muscle Strength and Training in Stroke and Neurology: A Systematic Review

We undertook two systematic reviews to determine the levels of respiratory muscle weakness and effects of respiratory muscle training in stroke patients. Two systematic reviews were conducted in June 2011 using a number of electronic databases. Review 1 compared respiratory muscle strength in stroke and healthy controls. Review 2 was expanded to include randomized controlled trials assessing the effects of respiratory muscle training on stroke and other neurological conditions. The primary outcomes of interest were maximum inspiratory and expiratory mouth pressure (maximum inspiratory pressure and maximum expiratory pressure, respectively). Meta-analysis of four studies revealed that the maximum inspiratory pressure and maximum expiratory pressure were significantly lower (P < 0·00001) in stroke patients compared with healthy individuals (weighted mean difference −41·39 and −54·62 cmH2O, respectively). Nine randomized controlled trials indicate a significantly (P = 0·0009) greater effect of respiratory muscle training on maximum inspiratory pressure in neurological patients compared with control subjects (weighted mean difference 6·94 cmH2O) while no effect on maximum expiratory pressure. Respiratory muscle strength appears to be impaired after stroke, possibly contributing to increased incidence of chest infection. Respiratory muscle training can improve inspiratory but not expiratory muscle strength in neurological conditions, although the paucity of studies in the area and considerable variability between them is a limiting factor. Respiratory muscle training may improve respiratory muscle function in neurological conditions, but its clinical benefit remains unknown.

Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood

It is widely accepted that aging is accompanied by remodelling of the immune system including thymic atrophy and increased frequency of senescent T cells, leading to immune compromise. However, physical activity, which influences immunity but declines dramatically with age, is not considered in this literature. We assessed immune profiles in 125 adults (55–79 years) who had maintained a high level of physical activity (cycling) for much of their adult lives, 75 age‐matched older adults and 55 young adults not involved in regular exercise. The frequency of naïve T cells and recent thymic emigrants (RTE) were both higher in cyclists compared with inactive elders, and RTE frequency in cyclists was no different to young adults. Compared with their less active counterparts, the cyclists had significantly higher serum levels of the thymoprotective cytokine IL‐7 and lower IL‐6, which promotes thymic atrophy. Cyclists also showed additional evidence of reduced immunesenescence, namely lower Th17 polarization and higher B regulatory cell frequency than inactive elders. Physical activity did not protect against all aspects of immunesenescence: CD28−veCD57+ve senescent CD8 T‐cell frequency did not differ between cyclists and inactive elders. We conclude that many features of immunesenescence may be driven by reduced physical activity with age.

Properties of the vastus lateralis muscle in relation to age and physiological function in master cyclists aged 55–79 years

In this study, results are reported from the analyses of vastus lateralis muscle biopsy samples obtained from a subset (n = 90) of 125 previously phenotyped, highly active male and female cyclists aged 55–79 years in regard to age. We then subsequently attempted to uncover associations between the findings in muscle and in vivo physiological functions. Muscle fibre type and composition (ATPase histochemistry), size (morphometry), capillary density (immunohistochemistry) and mitochondrial protein content (Western blot) in relation to age were determined in the biopsy specimens. Aside from an age‐related change in capillary density in males (r = −.299; p = .02), no other parameter measured in the muscle samples showed an association with age. However, in males type I fibres and capillarity (p < .05) were significantly associated with training volume, maximal oxygen uptake, oxygen uptake kinetics and ventilatory threshold. In females, the only association observed was between capillarity and training volume (p < .05). In males, both type II fibre proportion and area (p < .05) were associated with peak power during sprint cycling and with maximal rate of torque development during a maximal voluntary isometric contraction. Mitochondrial protein content was not associated with any cardiorespiratory parameter in either males or females (p > .05). We conclude in this highly active cohort, selected to mitigate most of the effects of inactivity, that there is little evidence of age‐related changes in the properties of VL muscle across the age range studied. By contrast, some of these muscle characteristics were correlated with in vivo physiological indices.

Cardiorespiratory fitness not sedentary time or physical activity is associated with cardiometabolic risk in active older adults

Sedentary time (ST) and moderate‐to‐vigorous physical activity (MVPA) are associated with cardiometabolic health. Cardiorespiratory fitness (CRF) is also implicated but often overlooked in health recommendations. This study assessed the relationships between ST, MVPA, CRF, and cardiometabolic health in highly active older individuals. 125 healthy amateur cyclists aged 55 to 79 years had their ST and MVPA levels assessed by actigraphy over a 7‐day period. CRF was assessed using a maximal effort cycle ergometry test to determine VO2max with results normalized to both body mass and fat‐free mass measured by DXA. Markers of cardiometabolic risk (blood glucose, triglycerides, cholesterol, HDL, LDL, Insulin, HOMA IR, blood pressure, and body fat) were assessed and used to determine cumulative cardiometabolic risk. Multiple linear regression was used to assess ST, MVPA, and CRF associations with cardiometabolic health with the relationship between activity levels and CRF determined. CRF was associated with training volume (P = .003), but not ST or MVPA. A high CRF was associated with lower cumulative cardiometabolic risk, body fat percentage, triglyceride, and HDL levels (P < .05 in all cases). MVPA was negatively associated with body fat percentage, while ST was not associated with any marker of cardiometabolic risk when adjusting for activity levels. An association between CRF and cardiometabolic risk even in a group of older individuals with high fitness levels highlights the importance that CRF may have in maintaining health.

Human physiological and metabolic responses to an attempted winter crossing of Antarctica: the effects of prolonged hypobaric hypoxia.

An insufficient supply of oxygen to the tissues (hypoxia), as is experienced upon high‐altitude exposure, elicits physiological acclimatization mechanisms alongside metabolic remodeling. Details of the integrative adaptive processes in response to chronic hypobaric hypoxic exposure remain to be sufficiently investigated. In this small applied field study, subjects (n = 5, male, age 28–54 years) undertook a 40 week Antarctica expedition in the winter months, which included 24 weeks residing above 2500 m. Measurements taken pre‐ and postexpedition revealed alterations to glucose and fatty acid resonances within the serum metabolic profile, a 7.8 (±3.6)% increase in respiratory exchange ratio measured during incremental exercise (area under curve, P > 0.01, mean ± SD) and a 2.1(±0.8) % decrease in fat tissue (P < 0.05) postexpedition. This was accompanied by an 11.6 (±1.9) % increase (P > 0.001) in VO2 max corrected to % lean mass postexpedition. In addition, spine bone mineral density and lung function measures were identified as novel parameters of interest. This study provides, an in‐depth characterization of the responses to chronic hypobaric hypoxic exposure in one of the most hostile environments on Earth.

Physiological and metabolic responses to prolonged hypoxia and extreme cold: Preliminary data from the White Mars Antarctica winter expedition.

The Antarctic winter is amongst the most extreme environments on earth. Human adaptation to this environment, where severe cold is coupled with moderate altitudes, is poorly understood. In this study, a number of physiological and metabolic measurements were made on a small group of trekkers before and after an attempted winter crossing of Antarctica (White Mars Expedition).