Jonathan Peter Farthing

This study examined the influence of lateral constraints and sex on walking in different settings. Thirty-eight adults (17 males: 25 [3] y, 21 females: 24 [4] y) walked overground for 20 m in open (no constraints), open pathway (defined by lines on the floor), and hallway (pathway defined by walls) settings at 3 speeds (slow, preferred, and fast). Inertial sensors recorded kinematics (Xsens Awinda, Movella) to calculate stride velocity, stride length (SL), cadence, and double support phase percentage. Stride velocity, SL, and cadence were also normalized to account for body size. Linear mixed models were used for statistical analysis ( α = .05). No setting or setting by speed effects were found. Males had greater SL compared with females at preferred and fast speeds. Males had greater normalized SL compared with females at fast speeds. Females had greater cadence compared with males across conditions. Males had greater double support phase percentage compared with females at slow speeds. Wider hallways may allow for walking assessments generalizable to open settings. Considering sex differences in cadence at any speed, SL at preferred and fast speeds, normalized SL at fast speeds, and double support phase percentage at slow speeds may be valuable for interpreting walking assessments.

Introduction: The neural pathways that contribute to force production in humans are currently poorly understood, as the relative roles of the corticospinal tract and brainstem pathways, such as the reticulospinal tract (RST), vary substantially across species. Using functional magnetic resonance imaging (fMRI) we aimed to measure activation in the pontine reticular nuclei (PRN) during different submaximal handgrip contractions to determine the potential role of the PRN in force modulation. Methods: Thirteen neurologically intact participants (age: 28 ± 6 years) performed unilateral handgrip contractions at 25%, 50%, 75% of maximum voluntary contraction during brain scans. We quantified the magnitude of PRN activation from the contralateral and ipsilateral sides during each of the three contraction intensities. Results: A repeated measures ANOVA demonstrated a significant main effect of force (p = 0.012, η_p² = 0.307) for PRN activation, independent of side (i.e., activation increased with force for both contralateral and ipsilateral nuclei). Further analyses of these data involved calculating the linear slope between the magnitude of activation and handgrip force for each region of interest (ROI) at the individual-level. One-sample t-tests on the slopes revealed significant group-level scaling for the PRN bilaterally, but only the ipsilateral PRN remained significant after correcting for multiple comparisons. Conclusions: We show evidence of task dependent activation in the PRN that was positively related to handgrip force. These data build on a growing body of literature that highlights the RST as a functionally relevant motor pathway for force modulation in humans.

Introduction: The neural pathways that contribute to force production in humans are currently poorly understood, as the relative roles of the corticospinal tract and brainstem pathways, such as the reticulospinal tract (RST), vary substantially across species. Using functional magnetic resonance imaging (fMRI) we aimed to measure activation in the pontine reticular nuclei during different submaximal handgrip contractions to determine the potential role of the RST in force modulation. Methods: Thirteen neurologically intact participants (age: 28 ± 6 years) performed unilateral handgrip contractions at 25%, 50%, 75% of maximum voluntary contraction during brain scans. We quantified the magnitude of RST activation from the contralateral and ipsilateral sides in addition to the contralateral primary motor cortex during each of the three contraction intensities. Results: A repeated measures ANOVA demonstrated a significant main effect of force ( p = 0.012, η _p ² = 0.307) for RST activation, independent of side (i.e., activation increased with force for both contralateral and ipsilateral nuclei). Further analyses of these data involved calculating the linear slope between the magnitude of activation and handgrip force for each ROI at the individual-level. One-sample t- tests on the slopes revealed significant group-level scaling for the RST bilaterally, but only the ipsilateral RST remained significant after correcting for multiple comparisons. Conclusions: Here, we show evidence of task dependent activation in the RST pontine nuclei that was positively related to handgrip force. These data build on a growing body of literature that highlights the RST as a functionally relevant motor pathway for force modulation in humans. New & Noteworthy: In this short report, we used a task-based fMRI paradigm to show that activity in the reticulospinal tract, but not the contralateral motor cortex, scales linearly with increasing force during a handgrip task. These findings directly support recently proposed hypotheses that the reticulospinal tract may play an important role in modulating force production in humans.

This review examines the experimental evidence regarding unilateral resistance training frequency, intensity, the type of training, training volume, and adjuvant therapies on the cross-education of strength. CINAHL, MEDLINE, APA PsycInfo, SPORTDiscus, and Web of Science were systematically searched with gray literature searches and pearling of references thereafter. Experiments were included in the review if they performed a unilateral resistance training intervention that directly compared the dose of a training variable on the cross-education response in healthy or clinical populations following a minimum of two weeks of training. Experiments must have reported maximal strength outcomes for the untrained limb. For each experiment, the study population, intervention methods, the dosage of the training variable being studied, and the outcomes for the untrained, contralateral limb were identified and collectively synthesized. The search returned a total of 912 articles, 57 of which qualified for inclusion. The results show that experimental trials have been conducted on resistance training frequency ( n = 4), intensity ( n = 7), the type of training ( n = 26), training volume ( n = 3), and adjuvant therapies ( n = 17) on the cross-education of strength. This review maps the available evidence regarding exercise design and prescription strategies to promote the cross-education of strength. It appears that traditional resistance training frequencies (i.e., 2–3×/week) at high intensities are effective at promoting cross-education with eccentric muscle actions showing additive benefits. There is experimental evidence that neuromodulatory techniques can augment cross-education when layered with unilateral resistance training versus training alone. Registration identifier (osf.io/9sh5b). The cross-education of strength is moderated by exercise design and prescription in clinical and non-clinical populations. This review synthesizes the available evidence regarding exercise design strategies for unilateral resistance training and provides evidence-based recommendations for the prescription of unilateral training to maximize the cross-education of strength. Greater insights regarding the timing and effectiveness of cross-education interventions in clinical scenarios will strengthen the use of unilateral resistance training for individuals who may benefit from its use.

Objective: To perform a scoping review of the literature on the experimental studies examining the role of resistance training frequency, intensity, the type of training, training volume, and adjuvant therapies on the cross-education of strength. Study Design: Scoping Review. Literature Search: The review was preregistered and performed with the search methodology described by the PRISMA extension for scoping reviews. CINAHL, MEDLINE, APA PsycInfo, SPORTDiscus, and Web of Science were systematically searched with grey literature searches and pearling of references thereafter. Study Selection Criteria: Experiments were included in the review if they performed a unilateral resistance training intervention that directly compared the dose of a training variable on the cross-education response in healthy or clinical populations following a minimum of two weeks of training. Experiments must have reported maximal strength outcomes for the untrained limb. Data Synthesis: For each experiment, the study population, intervention methods, the dosage of the training variable being studied, and the outcomes for the untrained, contralateral limb were identified and collectively synthesized. Results: The search returned a total of 911 articles, 56 of which qualified for inclusion. The results show that experimental trials have been conducted on resistance training frequency (n = 4), intensity (n = 7), the type of training (n = 25), training volume (n = 3), and adjuvant therapies (n = 17) on the cross-education of strength. Conclusions: This review synthesizes the available evidence regarding exercise design and prescription strategies to promote the cross-education of strength. It appears that traditional resistance training frequencies (ie., 2-3d/wk) at high intensities are effective at promoting cross- education. Eccentric muscle actions show additive benefits. There is experimental evidence that neuromodulatory techniques can augment cross-education when layered with unilateral resistance training versus training alone.

Introduction: Exercise can decrease fall risk in older adults but less is known about training to reduce injury risk in the event a fall is unavoidable. The purpose of this study was to compare standard fall prevention exercises to novel Fall Arrest Strategy Training ( FAST); exercises designed to improve upper body capacity to reduce fall-injury risk in older women. Method: Forty women (mean age 74.5 years) participated in either Standard (n = 19) or FAST (n = 21) twice per week for 12 weeks. Both interventions included lower body strength, balance, walking practice, agility and education. FAST added exercises designed to enhance forward landing and descent control such as upper body strengthening, speed and practice of landing and descent on outstretched hands. Results: Both FAST and Standard significantly improved strength, mobility, balance, and fall risk factors from pre to post-intervention. There was a significant time by group interaction effect for upper body response time where FAST improved but Standard did not ( p = 0.038). Discussion: FAST resulted in similar gains in factors that reduce fall risk as a standard fall prevention program; with the additional benefit of improving speed of arm protective responses; a factor that may help enhance landing position and reduce injury risks such as head impact during a forward fall.

In humans, motor learning is underpinned by changes in functional connectivity (FC) across the sensorimotor network. Unilateral exercise-induced fatigue increases FC in the ipsilateral primary motor cortex (M1) and supplementary motor area (SMA); areas involved in motor planning and execution of the contralateral hand. Unilateral fatiguing exercise is therefore a promising potential approach to augment motor performance in the non-fatigued, contralateral, hand. In a within-participant, controlled, randomized, cross-over design, 15 right-handed adults had two magnetic resonance imaging (MRI) sessions, where functional MRI and MR Spectroscopic Imaging were acquired before and after repeated right-hand contractions at either 5% or 50% maximum voluntary contraction (MVC). Before and after scanning, response times (RTs) were determined in both hands, and after scanning, participants performed a serial reaction time task (SRTT) with their left, unfatigued, hand. Nine minutes of 50% MVC contractions resulted in fatigue. This unimanual fatigue improved motor performance, as indexed by decreased RTs, in the contralateral hand. Although fatigue had no significant effects on sequence learning, fatigue led to a significant increase in the transfer of the learned skill to the untrained hand. These behavioural effects were supported by significant neural changes: an increase in SMA-SMA functional connectivity, and increased connectivity between right M1 and right Orbitofrontal Cortex. At a neurochemical level, the degree of fatigue-induced decrease in GABA in left M1, left and right SMA correlated with subsequent behavioural improvements in the left-hand. These results support unilateral fatiguing exercise as a potential therapeutic intervention in a range of neurological and orthopedic conditions. Key points summary Right handgrip contractions at 50% MVC improve left hand response times. Repeated handgrip contractions at 50% MVC alter interhemispheric functional connectivity. Unilateral exercise may be an effective method for enhancing contralateral limb motor performance in rehabilitation settings.