Dr Ken Howells

High-intensity exercise induces significant central and peripheral fatigue, however the effect of endurance training on these mechanisms of fatigue is poorly understood. We compared the effect of cycling endurance training of disparate intensities on high-intensity exercise endurance capacity and the associated limiting central and peripheral fatigue mechanisms. Twenty adults were randomly assigned to 6 weeks of either high-intensity interval training (HIIT, 6-8 × 5 min at halfway between lactate threshold and maximal oxygen uptake [50%Δ]) or volume matched moderate-intensity continuous training (CONT, ~60-80 min at 90% lactate threshold). Two time to exhaustion (TTE) trials at 50%Δ were completed pre- and post-training to assess endurance capacity; the two post-training trials were completed at the pre-training 50%Δ (same absolute intensity) and the ‘new’ post-training 50%Δ (same relative intensity). Pre- and post-exercise responses to femoral nerve and motor cortex stimulation were examined to determine peripheral and central fatigue, respectively. HIIT resulted in greater increases in TTE at the same absolute and relative intensities as pre-training (148% and 43%, respectively) compared with CONT (38% and −4%, respectively). Compared with pre-training, HIIT increased the level of potentiated quadriceps twitch reduction (−34% vs −43%, respectively) and attenuated the level of voluntary activation reduction (−7% vs −3%, respectively) following the TTE trial at the same relative intensity. There were no other training effects on neuromuscular fatigue development. This suggests that central fatigue resistance contributes to enhanced high-intensity exercise endurance capacity after HIIT by allowing greater performance to be extruded from the muscle.

The aim of this study was to monitor muscle contractile performance in vivo, using an electrical stimulation protocol, immediately following an acute high and low intensity exercise session conducted at the same average intensity performed on a cycle ergometer. Eighteen healthy males (25.1 +/- A 4.5 years, 81.6 +/- A 9.8 kg, 1.83 +/- A 0.06 m; mean +/- A SD) participated in the study. On two occasions, separated by 1 week, subjects completed a high and low intensity exercise session in a random order on a cycle ergometer, performing equal total work in each. At the end of each test, a muscle performance test using electrical stimulation was performed within 120 s. Post-exercise muscle data were compared to the subjects' rested muscle. We found a reduction in muscle contractile performance following both high and low intensity exercise protocols but a greater reduction in maximal voluntary contraction (MVC) (P < 0.01), rate of torque development (RTD) (P < 0.001), rate of relaxation (RR(A1/2)), (P < 0.001) the 60 s slope of the fatigue protocol (P < 0.01) and torque frequency response (P < 0.05) following the high intensity bout. Importantly muscle performance remained reduced 1 h following high intensity exercise but was recovered following low intensity exercise. Muscle function was significantly reduced following higher intensity intermittent exercise in comparison to lower intensity exercise even when the average overall intensity was the same. This study is the first to demonstrate the sensitivity of muscle contractile characteristics to different exercise intensities and the impact of higher intensity bursts on muscle performance.

Walking models driven by centre of mass (CoM) data obtained from inertial measurement units (IMU) or optical motion capture systems (OMCS) can be used to objectively measure gait. However current models have only been validated within typical developed adults (TDA). The purpose of this study was to compare the projected CoM movement within Parkinson's disease (PD) measured by an IMU with data collected from an OMCS after which spatio-temporal gait measures were derived using an inverted pendulum model. The inter-rater reliability of spatio-temporal parameters was explored between expert researchers and clinicians using the IMU processed data. Participants walked 10 m with an IMU attached over their centre of mass which was simultaneously recorded by an OMCS. Data was collected on two occasions, each by an expert researcher and clinician. Ten people with PD showed no difference (p = 0.13) for vertical, translatory acceleration, velocity and relative position of the projected centre of mass between IMU and OMCS data. Furthermore no difference (p = 0.18) was found for the derived step time, stride length and walking speed for people with PD. Measurements of step time (p = 0.299), stride length (p = 0.883) and walking speed (p = 0.751) did not differ between experts and clinicians. There was good inter-rater reliability for these parameters (ICC3.1 = 0.979. ICC3.1 = 0.958 and ICC3.1 = 0.978, respectively). The findings are encouraging and support the use of IMUs by clinicians to measure CoM movement in people with PD.

Laboratory based gait analysis techniques are expensive, time consuming and require technical expertise. Inertial measurement units can directly measure temporal parameters and in combination with gait models may provide a solution to obtain spatial gait measurements within daily clinical assessments. However it is not known if a model and standard correction factor determined by Zijlstra and Hof [8] to estimate step and stride length parameters in typically developed adults (TDA) can be accurately used in neurologically impaired gaits.This research estimated the stride length over two 10 m walks at self selected walking speed in people with neurological conditions, using a previously established model and correction factor for TDA. The relation of the correction factor to walking speed was explored. We recruited TDA (n = 10) and participants with Parkinson's disease (PD; n = 24), muscular dystrophy (MD; n = 13), motor neuron disease (MND; n = 7) and stroke survivors (n = 18) for the study who twice walked 10 m at a self-selected pace. Stride length correction factors, for TDA (1.25 +/- 0.01), PD (1.25 +/- 0.03), and MD (1.21 +/- 0.08) (p = 0.833 and p = 0.242) were the same as previously reported in TDA (Zijlstra and Hof [8]). Correction factors for stroke (1.17 +/- 0.42) and MND (1.10 +/- 0.08) were different (p < 0.01 and p = 0.028 respectively). However there was a high level of variability for correction factors within groups, which did not relate to walking speed. Our findings support that correction factors should be determined for each individual to estimate average step/stride length in patients suffering from a neurological condition.

Background and Purpose-Stroke patients often have difficulties in simultaneously performing a motor and cognitive task. Functional imaging studies have shown that movement of an affected hand after stroke is associated with increased activity in multiple cortical areas, particularly in the contralesional hemisphere. We hypothesized patients for whom executing simple movements demands greater selective attention will show greater brain activity during movement. Methods-Eight chronic stroke patients performed a behavioral interference test using a visuo-motor tracking with and without a simultaneous cognitive task. The magnitude of behavioral task decrement under cognitive motor interference (CMI) conditions was calculated for each subject. Functional MRI was used to assess brain activity in the same patients during performance of a visuo-motor tracking task alone; correlations between CMI score and movement-related brain activation were then explored. Results-Movement-related activation in the dorsal precentral gyrus of the contralesional hemisphere correlated strongly and positively with CMI score (r(2) at peak voxel=0.92; P<0.05). Similar but weaker relationships were observed in the ventral precentral and middle frontal gyrus. There was no independent relationship between hand motor impairment and CMI. Conclusions-Results suggest that variations in the degree to which a cognitive task interferes with performance of a concurrent motor task explains a substantial proportion of the variations in movement-related brain activity in patients after stroke. The results emphasize the importance of considering cognitive context when interpreting brain activity patterns and provide a rationale for further evaluation of integrated cognitive and movement interventions for rehabilitation in stroke. (Stroke. 2011;42:1056-1061.)

Dual-task methodology has been increasingly used to assess cognitive motor interference while walking. However, whether the observed dual-task-related gait changes are systematically related to methodological variations remains unclear and researchers still lack knowledge of what cognitive task to use in different groups for clinical purposes or for research. We systematically reviewed experimental studies that measured gait performance with and without performing concurrent cognitive task. Our results suggest that cognitive tasks that involve internal interfering factors seem to disturb gait performance more than those involving external interfering factors. Meta-analysis results show that the overall effect of different cognitive tasks was prominent in gait speed. In healthy participants, meta-regression analysis suggests strong associations between age and speed reduction under dual-task conditions and between the level of cognitive state and speed reduction under dual-task conditions. Standardizing research methodologies, as well as improving their ecological validity, enables better understanding of dual-task-related gait changes in different populations and improves, in turn, our understanding of neural mechanisms and gait control in general in content.

Purpose. Bladder dysfunction and disability may cause people with multiple sclerosis (pwMS) to limit fluid intake. However, hydration is rarely considered in the multiple sclerosis literature. We investigated the hydration status of people with pwMS and its association with independence in activities of daily living. Methods. Twenty-six (six men) pwMS over 18 years old and able to walk with or without an aid took part in the study. Hydration status was measured via urine osmolality, with adequate hydration defined as an osmolality <= 500 (mOsm kg(-1)). Independence in daily activities was measured using the Barthel index. Results. Mean urine osmolality was 470+/-209 mOsm kg(-1) and indicated 11 (42%) participants were not adequately hydrated. Independence in daily activities could partly explain hydration status (R(2) = 0.209, p<0.05). Additionally there was a trend for men to be less well hydrated than women. Conclusions. The results indicate that some pwMS were not adequately hydrated and that this could be partly explained by disability. Implications of reducing and maintaining fluid levels on function and quality of life in relation to bladder dysfunction and disability in pwMS should be investigated.

We investigated the relationship between muscle contractile characteristics, collected using percutaneous electrical stimulation, and high-intensity exercise performance. Seventeen participants performed a muscle performance test for the calculation of rate of torque development (RTD), rate of relaxation (RR(1/2)), rate of fatigue and fatigue resistance. On a second visit the participants completed a Wingate cycle ergometer test with peak power, mean power, fatigue index and fatigue rate calculated. The muscle fatigue index related significantly to the WAnT fatigue index and fatigue rate (p < 0.01). The change in rate of torque development (%Delta RTD) was also related significantly to the fatigue rate (W/s) during the WAnT. Subjects displaying the greatest reduction in RTD had the greatest fatigue rate during the WAnT and greater fatigue during the electrical stimulation protocol. There were no significant relationships between peak (r 0.36; p > 0.01) or mean power (r -0.11, p > 0.01) with any of the muscle performance measures. These findings demonstrate that muscle contractile characteristics, elicited during standardised in vivo electrical stimulation, relate to performance during a Wingate anaerobic test. They suggest that muscle contraction characteristics play an important role in high-intensity exercise performance and indicate that electrical stimulation protocols can be a useful additional tool to explore muscle contraction characteristics in relation to exercise performance and trainability.

Gait in stroke patients is often characterised by slower speeds, which may be exacerbated by situations that combine gait with a cognitive task, leading to difficulties with everyday activities. Interaction between cognitive task performance and gait speed may differ according to walking intensity. This study examines the effects of two cognitive tasks on gait at preferred walking pace, and at a faster pace, using dual-task methodology. 21 chronic stroke patients and 10 age-matched control subjects performed 2 single motor tasks (walking at preferred and at fast pace around a walkway), and two cognitive tasks (serial subtractions of 3s and a visual-spatial decision task) under single- and dual-task conditions (cognitive-motor interference) in a randomised order. Cognitive task score and gait speed were measured. The healthy control group showed no effects of CMI. The stroke group decreased their walking speed whilst concurrently performing serial 3s during both preferred and fast walking trials and made more mistakes in the visuo-spatial task during fast walking. There was no effect of walking on the serial 3 performance. The findings show that in stroke patients, during walking whilst concurrently counting backwards in 3s the cognitive task appeared to take priority over maintenance of walking speed. During fast walking whilst concurrently performing a visuo-spatial imagery task, they appeared to favour walking. This may indicate that people spontaneously favour one activity over the other, which has implications for gait rehabilitation.

Previous studies have shown that walking is not a purely automatic motor task but places demands on sensory and cognitive systems. We set out to investigate whether complex walking tasks, as when walking down a steeper gradient while performing a concurrent cognitive task, would demand gait adaptation beyond those required for walking under low-challenge conditions. Thirteen healthy young individuals walked at their self-selected speed on a treadmill at different inclinations (0, 5 and 10%). Gait spatio-temporal measures, pelvis angular excursion, and sacral centre of mass (CoM) motion were acquired while walking or while walking and performing a mental tracking task. Repeated-measures ANOVAs revealed that decreasing treadmill inclination from 0 to 10% resulted in significant decreased walking speed (P < 0.001), decreased stride length (P < 0.001), increased pelvis tilt (P = 0.006) and obliquity variability (P = 0.05), decreased pelvis rotation (P = 0.02), and increased anterio-posterior (A-P) CoM displacement (P = 0.015). Compared to walking alone, walking under dual-task condition resulted in increased step width (P < 0.001), and increased medio-lateral (M-L) CoM displacement (P = 0.039) regardless of inclination grade, while sagittal plane dynamics did not change. Findings suggest that gait adapts differently to cognitive and mechanical constraints; the cognitive system is more actively involved in controlling frontal than sagittal plane gait dynamics, while the reverse is true for the mechanical system. Finally, these findings suggest that gait adaptations maintain the ability to perform concurrent tasks while treadmill walking in healthy young adults.

The purpose of this study was to use a quaternion rotation matrix in combination with an integration approach to transform translatory accelerations of the centre of mass (CoM) from an inertial measurement unit (IMU) during walking, from the object system onto the global frame. Second, this paper utilises double integration to determine the relative change in position of the CoM from the vertical acceleration data. Five participants were tested in which an IMU, consisting of accelerometers, gyroscopes and magnetometers was attached on the lower spine estimated centre of mass. Participants were asked to walk three timed through a calibrated volume at their self-selected walking speed. Synchronized data were collected by an IMU and an optical motion capture system (OMCS); both measured at 100 Hz. Accelerations of the IMU were transposed onto the global frame using a quaternion rotation matrix. Translatory acceleration, speed and relative change in position from the IMU were compared with the derived data from the OMCS. Peak acceleration in vertical axis showed no significant difference (p >= 0.05). Difference between peak and trough speed showed significant difference (p < 0.05) but relative peak-trough position between the IMU and OMCS did not show any significant difference (p >= 0.05). These results indicate that quaternions, in combination with Simpsons rule integration, can be used in transforming translatory acceleration from the object frame to the global frame and therefore obtain relative change in position, thus offering a solution for using accelerometers in accurate global frame kinematic gait analyses.

Objective: To examine the accuracy of measuring step counts using a pedometer in participants with neurological conditions and healthy volunteers in relation to a manual step count tally. Setting: Oxford Centre for Enablement, Nuffield Orthopaedic Centre NHS Trust, Oxford, UK. Subjects: Healthy adults (n¼13, age: mean 29, SD¼12) and adults with neurological conditions (n¼20 stroke, n¼16 multiple sclerosis, n¼5 muscular dystrophy, n¼1 spinal cord injury, n¼1 traumatic brain injury; age: mean 54, SD¼13). Main measures: Individuals walked for 2 minutes at self-selected walking speeds (SSWS) wearing a pedometer. Healthy individuals were then asked to walk at slow walking speeds (SWS). Step counts were recorded manually and using a pedometer. Results: In healthy individuals there was no difference between manually measured and pedometer counts during walking (P40.05). In adults with neurological conditions the pedometers undercounted (P¼0.003); bias (random error): 27 (111); percentage variability 30% and intraclass correlation coefficient (ICC) 0.66. In neurological adults, from regression analysis the relationship between error and walking speed was cubic, with walking speed accounting for 29% of pedometer error. Healthy individuals showed greater variability and undercounting at SWS bias (random error): 10 (31), percentage variability 8% and ICC 0.73, compared with SSWS bias (random error): -3 (13), percentage variability 3% and ICC 0.84. Conclusions: Pedometers may undercount when used for people with neurological conditions. There may be variability in pedometer accuracy but this was not strongly related to walking speed. The suitability of pedometer use for exercise monitoring should be individually determined.

The aim of this study was to examine the relationship of a range of in-vivo whole muscle characteristics to determinants of endurance performance. Eleven healthy males completed a cycle ergometer step test to exhaustion for the determination of the lactate threshold, gross mechanical efficiency, peak power and VO(2)max. On two separate occasions, contractile and fatigue characteristics of the quadriceps femoris were collected using a specially designed isometric strength-testing chair. Muscle fatigue was then assessed by stimulating the muscle for 3 minutes. Force, rate of force development and rates of relaxation were calculated at the beginning and end of the 3 minute protocol and examined for reliability and in relation to lactate threshold, VO(2)max, gross mechanical efficiency and peak power. Muscle characteristics, rate of force development and relaxation rate were demonstrated to be reliable measures. Force drop off over the 3 minutes (fatigue index) was related to lactate threshold (r = -0.72 p < 0.01) but not to VO(2)max. The rate of force development related to the peak power at the end of the cycle ergometer test (r = -0.75 p < 0.01). Rates of relaxation did not relate to any of the performance markers. We found in-vivo whole muscle characteristics, such as the fatigue index and rate of force development, relate to specific markers of peripheral, but not to central, fitness components. Our investigation suggests that muscle characteristics assessed in this way is reliable and could be feasibly utilised to further our understanding of the peripheral factors underpinning performance.