Courtney L. Pollock

Validation of the Fitbit One activity monitor device during treadmill walking

OBJECTIVES In order to quantify the effects of physical activity such as walking on chronic disease, accurate measurement of physical activity is needed. The objective of this study was to determine the validity and reliability of a new activity monitor, the Fitbit One, in a population of healthy adults. DESIGN Cross-sectional study. METHODS Thirty healthy adults ambulated at 5 different speeds (0.90, 1.12, 1.33, 1.54, 1.78 m/s) on a treadmill while wearing three Fitbit One activity monitors (two on the hips and one in the pocket). The order of each speed condition was randomized. Fitbit One step count output was compared to observer counts and distance output was compared to the calibrated treadmill output. Two-way repeated measures ANOVA, concordance correlation coefficients, and Bland and Altman plots were used to assess validity and intra-class correlation coefficients (ICC) were used to assess reliability. RESULTS No significant differences were noted between Fitbit One step count outputs and observer counts, and concordance was substantial (0.97-1.00). Inter-device reliability of the step count was high for all walking speeds (ICC ≥ 0.95). Percent relative error was less than 1.3%. The distance output of the Fitbit One activity monitors was significantly different from the criterion values for each monitor at all speeds (P<0.001) and exhibited poor concordance (0.0-0.05). Inter-device reliability was excellent for all treadmill speeds (ICC ≥ 0.90). Percent relative error was high (up to 39.6%). CONCLUSIONS The Fitbit One activity monitors are valid and reliable devices for measuring step counts in healthy young adults. The distance output of the monitors is inaccurate and should be noted with caution.

Clinical measurement of walking balance in people post stroke: a systematic review

Objective: To identify walking balance measures which have been established for use with ambulatory people post stroke and reflect the balance requirements of community walking. Data sources: MEDLINE, Embase, AMED. Review methods: Measures reflecting walking balance, with tasks that include a stepping action in standing, used with people post stroke were reviewed. Measures with clinical utility were evaluated for psychometric properties, including reliability, validity and clinical interpretation. Results: Nine measures (24 papers) were identified that met the requirement of measuring walking balance in people post stroke with demonstrated clinical utility. Outcome measures with multiple tasks (Brunel Balance Assessment, Modified Emory Functional Ambulation Profile, Dynamic Gait Index, Community Balance and Mobility Scale, and mini-Balance Evaluation Systems Test) as opposed to single task measures (Step Test, Side Step Test and Four Square Step Test, Timed Up and Go), reflect a broader range of walking balance required to accommodate the variable challenges which may be expected at the community level of walking. Most tools report excellent reliability when used by physiotherapists. Validity remains far more challenging to establish. Evaluation of clinical interpretation is limited for all measures. Conclusion: The multiple-task outcome measures reviewed reflected walking balance activities often undertaken during community mobility. Single-task measures may be useful as screening measures, identifying walking balance deficits associated with basic/lower levels of walking balance. Construct validity and clinical interpretability of each measure in ambulatory people post stroke requires further research to identify the level of community mobility represented by each measure of walking balance.

Electromyography and Kinematics of the Trunk during Rowing in Elite Female Rowers

PURPOSE The purpose of this study was to characterize the EMG of trunk muscles together with kinematics of the pelvis and the spine of elite female rowers during the rowing stroke. METHODS Nine Rowing Canada national team candidates performed a 2000-m race simulation. EMG activity of spinal and pelvic extensor and flexor muscles and kinematic data of the pelvis and the spine were collected and analyzed during the period of peak force production. RESULTS During this period, pelvic and spinal extensor muscles demonstrated similarities in the timing of muscle activity with minimal coactivation of flexors and extensors. Minimal excursion of spinal segments occurred during the stroke with most of the extension occurring at the pelvis. Flexor activity occurred toward late drive, suggesting that trunk extension is slowed by increasing activity of the flexor muscles. CONCLUSIONS This study provides data of trunk kinematics and muscle recruitment patterns in elite female rowers. During the period of peak force production, there is minimal coactivation of trunk flexor and extensor muscles and, of the spinal segments, L3-S1 shows the most movement, which may make it more susceptible to soft tissue injury.

Rib stress fracture in a male adaptive rower from the arms and shoulders sport class: Case report

Adaptive rowing is rowing or sculling for rowers with a physical disability. It debuted at the Paralympic Games in 2008. In order to ensure an equitable playing field, rowers with similar levels of physical function and disability are classified into different sport classes for competition. Rowers with an inability to use a sliding seat and impaired trunk function resulting in an inability to perform trunk forward and backward lean via hip flexion/extension are assigned to the Arms and Shoulders (AS) class. AS rowers have to use a chest strap set immediately below the chest in order to localize any trunk movement in AS class. Conditions created by adaptations of rowing equipment and technique within the AS class create unique stresses on the upper thoracic region. The following case report demonstrates how etiology and management of a rib stress fracture in an AS rower differs in comparison to able-body rowers. Of significant importance were the limitations imposed on the rower’s ability to maintain rowing-specific fitness, due to the nature of the rib stress fracture and requirement to decrease force transmission through the ribs for several weeks. The rower’s gradual return to full training was further impacted by obligatory use of the chest strap, which directly applied pressure over the injured area. Protective orthosis for the chest was designed and applied in order to dissipate pressure of the chest strap over the thorax during rowing (most importantly at the catch position) both on the ergometer and in the boat.

Use of the Challenge Point Framework to Guide Motor Learning of Stepping Reactions for Improved Balance Control in People With Stroke: A Case Series

Background and Purpose Stepping reactions are important for walking balance and community-level mobility. Stepping reactions of people with stroke are characterized by slow reaction times, poor coordination of motor responses, and low amplitude of movements, which may contribute to their decreased ability to recover their balance when challenged. An important aspect of rehabilitation of mobility after stroke is optimizing the motor learning associated with retraining effective stepping reactions. The Challenge Point Framework (CPF) is a model that can be used to promote motor learning through manipulation of conditions of practice to modify task difficulty, that is, the interaction of the skill of the learner and the difficulty of the task to be learned. This case series illustrates how the retraining of multidirectional stepping reactions may be informed by the CPF to improve balance function in people with stroke. Case Description Four people (53–68 years of age) with chronic stroke (>1 year) and mild to moderate motor recovery received 4 weeks of multidirectional stepping reaction retraining. Important tenets of motor learning were optimized for each person during retraining in accordance with the CPF. Outcomes Participants demonstrated improved community-level walking balance, as determined with the Community Balance and Mobility Scale. These improvements were evident 1 year later. Aspects of balance-related self-efficacy and movement kinematics also showed improvements during the course of the intervention. Discussion The application of CPF motor learning principles in the retraining of stepping reactions to improve community-level walking balance in people with chronic stroke appears to be promising. The CPF provides a plausible theoretical framework for the progression of functional task training in neurorehabilitation.

Between-day reliability of triceps surae responses to standing perturbations in people post-stroke and healthy controls: A high-density surface EMG investigation

The reliability of triceps surae electromyographic responses to standing perturbations in people after stroke and healthy controls is unknown. High-Density surface Electromyography (HDsEMG) is a technique that records electromyographic signals from different locations over a muscle, overcoming limitations of traditional surface EMG such as between-day differences in electrode placement. In this study, HDsEMG was used to measure responses from soleus (SOL, 18 channels) and medial and lateral gastrocnemius (MG and LG, 16 channels each) in 10 people after stroke and 10 controls. Timing and amplitude of the response were estimated for each channel of the grids. Intraclass Correlation Coefficient (ICC) and normalized Standard Error of Measurement (SEM%) were calculated for each channel individually (single-channel configuration) and on the median of each grid (all-channels configuration). Both timing (single-channel: ICC=0.75-0.96, SEM%=5.0-9.1; all-channels: ICC=0.85-0.97; SEM%=3.5-6.2%) and amplitude (single-channel: ICC=0.60-0.91, SEM%=25.1-46.6; ICC=0.73-0.95, SEM%=19.3-42.1) showed good-to-excellent reliability. HDsEMG provides reliable estimates of EMG responses to perturbations both in individuals after stroke and in healthy controls; reliability was marginally better for the all-channels compared to the single-channel configuration.

Behavior of medial gastrocnemius motor units during postural reactions to external perturbations after stroke

OBJECTIVE This study investigated the behavior of medial gastrocnemius (GM) motor units (MU) during external perturbations in standing in people with chronic stroke. METHODS GM MUs were recorded in standing while anteriorly-directed perturbations were introduced by applying loads of 1% body mass (BM) at the pelvis every 25-40s until 5% BM was maintained. Joint kinematics, surface electromyography (EMG), and force platform measurements were assessed. RESULTS Although external loads caused a forward progression of the anterior-posterior centre of pressure (APCOP), people with stroke decreased APCOP velocity and centre of mass (COM) velocity immediately following the highest perturbations, thereby limiting movement velocity in response to perturbations. MU firing rate did not increase with loading but the GM EMG magnitude increased, reflecting MU recruitment. MU inter spike interval (ISI) during the dynamic response was negatively correlated with COM velocity and hip angular velocity. CONCLUSIONS The GM utilized primarily MU recruitment to maintain standing during external perturbations. The lack of MU firing rate modulation occurred with a change in postural central set. However, the relationship of MU firing rate with kinematic variables suggests underlying long-loop responses may be somewhat intact after stroke. SIGNIFICANCE People with stroke demonstrate alterations in postural control strategies which may explain MU behavior with external perturbations.

Motor unit recruitment and firing rate in medial gastrocnemius muscles during external perturbations in standing in humans

There is limited investigation of the interaction between motor unit recruitment and rate coding for modulating force during standing or responding to external perturbations. Fifty-seven motor units were recorded from the medial gastrocnemius muscle with intramuscular electrodes in response to external perturbations in standing. Anteriorly directed perturbations were generated by applying loads in 0.45-kg increments at the pelvis every 25-40 s until 2.25 kg was maintained. Motor unit firing rate was calculated for the initial recruitment load and all subsequent loads during two epochs: 1) dynamic response to perturbation directly following each load drop and 2) maintenance of steady state between perturbations. Joint kinematics and surface electromyography (EMG) from lower extremities and force platform measurements were assessed. Application of the external loads resulted in a significant forward progression of the anterior-posterior center of pressure (AP COP) that was accompanied by modest changes in joint angles (<3°). Surface EMG increased more in medial gastrocnemius than in the other recorded muscles. At initial recruitment, motor unit firing rate immediately after the load drop was significantly lower than during subsequent load drops or during the steady state at the same load. There was a modest increase in motor unit firing rate immediately after the load drop on subsequent load drops associated with regaining balance. There was no effect of maintaining balance with increased load and forward progression of the AP COP on steady-state motor unit firing rate. The medial gastrocnemius utilized primarily motor unit recruitment to achieve the increased levels of activation necessary to maintain standing in the presence of external loads.

Motoneurone afterhyperpolarisation time-course following stroke

OBJECTIVE Our aim was to investigate any changes in the estimated time-course of the afterhyperpolarisation (AHP) in motoneurones innervating the tibialis anterior following stroke, with a secondary objective to compare the results from two different AHP estimation techniques. METHODS Motor units from tibialis anterior on the paretic and non-paretic sides of 15 subjects with chronic stroke were recorded using intramuscular electrodes during voluntary isometric contraction. Participants varied the motor unit firing rate from its lowest rate to approximately 10 Hz. The AHP duration was estimated using the interval death rate (IDR) and transition point methods. RESULTS The AHP decay time-constant was significantly different between sides (paretic: 41.7 ± 8.5 ms, non-paretic: 36.2 ± 6.4 ms). Additionally, the paretic AHP time-constant was significantly longer in participants with low motor recovery (45.9 ± 9.1 ms) than with high motor recovery (39.3 ± 10.0 ms) as measured by CMSA score. The AHP estimates from the two techniques were correlated (r=0.78). CONCLUSIONS The AHP time-course prolongation on the paretic side of people with chronic stroke is more pronounced in people with low motor recovery. SIGNIFICANCE Changes in the motoneurone AHP time course post-stroke were related to muscle function and may play a role in the commonly-observed reduction of motor unit discharge rate during voluntary contractions following stroke.

Reduced Quadriceps Motor-Evoked Potentials in an Individual with Unilateral Knee Osteoarthritis: A Case Report

One male with unilateral osteoarthritis (OA) of the knee underwent testing of corticospinal (CS) excitability (as quantified from motor-evoked potentials (MEPs) in the rectus femoris (RF) using transcranial magnetic stimulation) and quadriceps muscle strength. Baseline data indicated reduced MEP amplitudes in the RF of the affected limb compared to the unaffected limb. Increases in RF MEP amplitudes from both limbs were observed immediately following a 30-minute exercise session focusing on muscle strengthening. Following an 8-week muscle strengthening intervention, the participant exhibited increased MEP amplitudes and muscle strength in the affected limb. These findings suggest that alterations in peripheral muscle function found in patients with knee OA may have an origin centrally within the motor cortex and that interlimb differences may be evident in those with unilateral disease. These findings also suggest that CS excitability may be improved following a muscle strengthening intervention.