Susan Dewhurst

Effect of exercise training on neuromuscular function of elbow flexors and knee extensors of type 2 diabetic patients.

PURPOSE The effects of exercise training on neuromuscular function of arm and leg muscles in type 2 diabetic patients (T2D) was investigated. METHODS Eight T2D sedentary male patients (61.0±2.3years) and eight sedentary healthy age matched control subjects (H, 63.9±3.8years) underwent a 16-week supervised combined endurance and resistance exercise program. Before and after training, maximal isometric (MVIC), isokinetic (15, 30, 60, 120, 180, 240°s(-1)) torque and muscle endurance of the elbow flexors (EF) and knee extensors (KE) were assessed. Simultaneously, surface electromyographic signals from biceps brachii (BB) and vastus lateralis (VL) muscles were recorded and muscle fiber conduction velocity (MFCV) estimated. RESULTS Following training, maximal torque of the KE increased during MVIC and isokinetic contractions at 15 and 30°s(-1) in the T2D (+19.1±2.7% on average; p<0.05) but not in the H group (+7±0.9%; p>0.05). MFCV recorded from the VL during MVIC and during isokinetic contractions at 15 and 30°s(-1) increased (+11.2±1.6% on average; p<0.01), but in the diabetic group only. Muscular endurance was lower in T2D (20.1±0.7s) compared to H (26.9±1.3s), with an associated increase in the MFCV slope after training in the KE muscles only. CONCLUSION The effect of a combined exercise training on muscle torque appears to be angular velocity-specific in diabetic individuals, with a more pronounced effect on KE muscles and at slow contraction velocities, along with an associated increase in the MFCV. MFCV appears to be a more sensitive marker than torque in detecting the early signs of neuromuscular function reconditioning.

Scottish Country Dance: Benefits to Functional Ability in Older Women

The effects of long-term participation in Scottish country dance on body composition, functional ability, and balance in healthy older females were examined. Participants were grouped into dancers and physically active nondancers (ages 60-70 and 70-80 for both groups). Physical activity, body composition (body-mass index, skinfold thickness, waist-to-hip ratio), functional ability (6-min walk distance, 6-m walk time, 8-ft up-and-go time, lower body flexibility, shoulder flexibility), and static balance were measured. Younger dancers and physically active nondancers had similar 6-min walk distance, 6-m walk time, and 8-ft up-and-go time results; however, while older dancers performed similarly to younger dancers, older physically active nondancers performed poorer than their younger counterparts (p < .05). Body composition and static balance were the same for all groups. Regular physical activity can maintain body composition and postural stability with advancing age; however, Scottish country dance can delay the effects of aging on locomotion-related functional abilities.

Eye movements affect postural control in young and older females

Visual information is used for postural stabilization in humans. However, little is known about how eye movements prevalent in everyday life interact with the postural control system in older individuals. Therefore, the present study assessed the effects of stationary gaze fixations, smooth pursuits, and saccadic eye movements, with combinations of absent, fixed and oscillating large-field visual backgrounds to generate different forms of retinal flow, on postural control in healthy young and older females. Participants were presented with computer generated visual stimuli, whilst postural sway and gaze fixations were simultaneously assessed with a force platform and eye tracking equipment, respectively. The results showed that fixed backgrounds and stationary gaze fixations attenuated postural sway. In contrast, oscillating backgrounds and smooth pursuits increased postural sway. There were no differences regarding saccades. There were also no differences in postural sway or gaze errors between age groups in any visual condition. The stabilizing effect of the fixed visual stimuli show how retinal flow and extraocular factors guide postural adjustments. The destabilizing effect of oscillating visual backgrounds and smooth pursuits may be related to more challenging conditions for determining body shifts from retinal flow, and more complex extraocular signals, respectively. Because the older participants matched the young groups performance in all conditions, decreases of posture and gaze control during stance may not be a direct consequence of healthy aging. Further research examining extraocular and retinal mechanisms of balance control and the effects of eye movements, during locomotion, is needed to better inform fall prevention interventions.

Carrying shopping bags does not alter static postural stability and gait parameters in healthy older females

Food shopping is an important aspect of maintaining independence and social interaction in older age. Carriage of shopping bags alters the bodys weight distribution which, depending on load distribution, could potentially increase instability during standing and walking. The study examined the effect of carrying UK style shopping bags on static postural stability and gait in healthy older and young females. Nine older (71.0±6.0 years) and 10 young (26.7±5.2 years) females were assessed in five conditions carrying no bags, one 1.5kg bag in each hand, one 3kg bag in each hand, one 1.5kg bag in preferred hand, one 3kg bag in preferred hand. Antero-posterior and medio-lateral displacement, and 95% ellipse area from a 30s quiet standing were used for postural stability assessment. Stride length and its coefficient of variation, total double support time, step asymmetry and gait stability ratio were calculated from 1min treadmill walking at self-selected speed for gait assessment. Carrying shopping bags did not negatively affect postural stability or gait variables, in either group. Further, in older individuals, a decrease in sway velocity was found when holding bags during the postural stability assessment (p<0.05), suggesting that carriage of bags, irrespective of the load distribution, may have a stabilising effect during quiet standing. These results should help to alleviate concerns regarding safety of carrying shopping bags and help encourage shopping, both as a social and as a physical activity.

Homogeneity of fascicle architecture following repeated contractions in the human gastrocnemius medialis

This investigation sought to determine the effects of fatigue on fascicle architecture across the length of the human gastrocnemius medialis (GM). With institutional ethical approval, fifteen healthy males performed repeated isometric plantar flexion maximal voluntary contractions (MVC) until peak force fell 30% below baseline. Brightness-mode ultrasound was used to determine fascicle length and pennation angle at rest and during MVC prior to and following the fatiguing contractions. The results show a significant increase in fascicle length during MVC in the distal (2.8 mm, 8.1%) middle, (4.9 mm, 14.1%), and proximal (5.2 mm, 14.7%) regions post-fatigue compared to pre-fatigue (p < 0.05). There was also a significant decrease of pennation angle during MVC in the distal (3.3°, 8.8%), middle (3.9°, 9.4%), and proximal (2.9°, 6.9%) regions post-fatigue compared to pre-fatigue (p < 0.05). These changes, however, were not region specific. These are the first results to show that fascicle shortening within the GM remains homogeneous following fatigue, suggesting that the fascicles were fatigued in a similar pattern throughout the muscle. The significant reduction of fascicle shortening may reflect an additional strategy to maintain an optimal force output in fatigued conditions, although future work is needed to confirm this notion.

Mechanisms of head stability during gait initiation in young and older women: A neuro-mechanical analysis

Decreased head stability has been reported in older women during locomotor transitions such as the initiation of gait. The aim of the study was to investigate the neuro-mechanical mechanisms underpinning head stabilisation in young and older women during gait initiation. Eleven young (23.1 ± 1.1 yrs) and 12 older (73.9 ± 2.4 yrs) women initiated walking at comfortable speed while focussing on a fixed visual target at eye level. A stereophotogrammetric system was used to assess variability of angular displacement and RMS acceleration of the pelvis, trunk and head, and dynamic stability in the anteroposterior and mediolateral directions. Latency of muscle activation in the sternocleidomastoid, and upper and lower trunk muscles were determined by surface electromyography. Older displayed higher variability of head angular displacement, and a decreased ability to attenuate accelerations from trunk to head, compared to young in the anteroposterior but not mediolateral direction. Moreover, older displayed a delayed onset of sternocleidomastoid activation than young. In conclusion, the age-related decrease in head stability could be attributed to an impaired ability to attenuate accelerations from trunk to head along with delayed onset of neck muscles activation.

Validity and Reliability of Two Field-Based Leg Stiffness Devices: Implications for Practical Use

Leg stiffness is an important performance determinant in several sporting activities. This study evaluated the criterion-related validity and reliability of 2 field-based leg stiffness devices, Optojump NextR (Optojump) and Myotest ProR (Myotest) in different testing approaches. Thirty-four males performed, on 2 separate sessions, 3 trials of 7 maximal hops, synchronously recorded from a force platform (FP), Optojump and Myotest. Validity (Pearsons correlation coefficient, r; relative mean bias; 95% limits of agreement, 95%LoA) and reliability (coefficient of variation, CV; intraclass correlation coefficient, ICC; standard error of measurement, SEM) were calculated for first attempt, maximal attempt, and average across 3 trials. For all 3 methods, Optojump correlated highly to the FP (range r = .98-.99) with small bias (range 0.91-0.92, 95%LoA 0.86-0.98). Myotest demonstrated high correlation to FP (range r = .81-.86) with larger bias (range 1.92-1.93, 95%LoA 1.63-2.23). Optojump yielded a low CV (range 5.9% to 6.8%), high ICC (range 0.82-0.86), and SEM ranging 1.8-2.1 kN/m. Myotest had a larger CV (range 8.9% to 13.0%), moderate ICC (range 0.64-0.79), and SEM ranging from 6.3 to 8.9 kN/m. The findings present important information for these devices and support the use of a time-efficient single trial to assess leg stiffness in the field.

Intraday reliability and sensitivity of four functional ability tests in older women

ABSTRACT Functional tests are commonly used to evaluate the functional ability of older individuals; however, intraday reliability and sensitivity are required to enable informed decisions on whether repeated trials are necessary and to ensure that the values obtained from a single session are a patient’s true score. This study aimed to investigate the intraday reliability and sensitivity of four commonly used functional tests in older individuals. Seventy-one healthy older women (mean [SD]: age, 71.7 [7.3] yrs; body mass, 64.8 [10.2] kg; stature, 1.58 [0.07] m) performed the 6-m maximum walking speed, timed 8-foot up-and-go, chair sit-and-reach, and back scratch tests three times in one single session, with 1 min between trials. Reliability between all trials was examined using intraclass correlation coefficient, and sensitivity was examined using typical error. All tests were highly reliable (intraclass correlation coefficient range, 0.89–0.99), indicating no need for a familiarization trial. Typical error between trials 2 and 1 were 0.06 m·s−1, 0.42 s, 1.13 cm, 0.92 cm for the 6-m maximum walking speed, timed 8-foot up-and-go, chair sit-and-reach, and back scratch tests, respectively. Practitioners should perform two trials to examine whether the difference between them is less than the typical error reported here. These results should help practitioners ensure that scores obtained from an individual from these functional tests are a true reflection of their functional ability rather than measurement error.

Sodium bicarbonate ingestion improves Yo-Yo intermittent recovery test 1 performance: a randomized crossover trial

This study investigated the effect of sodium bicarbonate (NaHCO3-) ingestion on the Yo-Yo Intermittent Recovery Test 1 (IR1). We tested the hypotheses that acute ingestion of NaHCO3- would increase blood lactate concentrations [BLa], enhance performance and reduce ratings of perceived exertion in the Yo-Yo IR1. Eight recreationally active males (N=8, age 26±4 years, height 178±6 cm, body mass 82±10 kg) participated in the Yo-Yo IR1 on two separate occasions, separated by one week, in a randomized crossover design. Following familiarization, during seated rest, participants’ pre-test [BLa] were taken and participants then consumed either a placebo of 0.3 g·kg-1 body weight sodium chloride (NaCl), or 0.3 g·kg-1 body weight NaHCO3-. Sixty minutes post-ingestion, a standardized warm-up preceded the Yo-Yo IR1. Upon completion, post-exercise [BLa] (mmol·l-1), ratings of perceived exertion (RPE; arbitrary units) and Yo-Yo IR1 time to fatigue (s) were recorded. T-test revealed a small, but significantly improvement in Yo-Yo IR1 performance under the NaHCO3- condition (610± 267s), compared to placebo condition (556±259 s: p=0.01; Cohen’s d=0.20). Blood lactate increased more under the NaHCO3- condition (1.6±0.7 to 17.5±5.2 mmol·l-1; p<0.001; Cohen’s d=4.29) compared to the placebo condition (2.0±0.7 to 11.5±5.0 mmol·l-1; p=0.001; Cohen’s d=2.66). Post-exercise RPE was not significantly different between conditions. Results of this study suggest that acute NaHCO3- ingestion improves Yo-Yo IR1 performance without altering RPE, likely through an increased lactate efflux, demonstrated by increased [Bla].

Head flexion and different walking speeds do not affect gait stability in older females

Head flexion is destabilizing in older individuals during quiet stance, yet the effect head flexion has on gait is not known. The study examined whether head flexion and gait parameters were altered when walking freely and fixed to a visual target, at different walking speeds. 15 young (23±4years) and 16 older (76±6years) healthy females walked at three different walking speeds (slow, comfortable, and fast) under two visual conditions (natural and fixed [focusing on a visual target set at eye level]). Head flexion was assessed using 2D video analysis, whilst gait parameters (step length, double support time, step time, and gait stability ratio) were recorded during a 9m flat walkway. A mixed design ANOVA was performed for each variable, with age as the between-subject factor and, visual condition and walking speed as within-subject factors. When walking freely, older displayed a greater need for head flexion between walking speeds (P<0.05) when compared to young. Walking under fixed condition reduced head flexion at all walking speeds in the older (P<0.05), but had no effect on the young (P>0.05). Walking at different speeds showed no difference in head flexion when walking under either visual condition and had no effect on gait stability for both groups. Despite older displaying differences in head flexion between visual conditions, there was no effect on gait parameters. Walking speed presented trivial difference in head flexion in older females, whilst overall gait stability was unaffected by different walking speeds.