The effects of local forearm heating and cooling on motor unit properties during submaximal contractions.

New Findings: What is the central question of this study? How do temperature manipulations affect motor unit (MU) properties during submaximal contractions to the same relative percentage of maximal force? What is the main finding and its importance? MU recruitment patterns are affected by temperature manipulations at the forearm. However, the relationship between MU potential amplitude and recruitment threshold indicates no change to the order or recruitment. Additionally, the MU potential amplitude and firing rate relationship was affected by temperature, suggesting that smaller MUs are more affected by temperature changes than larger MUs.

Comparison of different wheelchair seating on thermoregulation and perceptual responses in thermoneutral and hot conditions in children.

We examined the effects of 4 different wheelchair seatings on physiological and perceptual measures in 21 healthy, pre-pubertal children (9 ± 2 years). Participants were able-bodied and did not regularly use a wheelchair. Participants sat for 2 h in Neutral (∼22.

The reliability of cutaneous low-frequency oscillations in young healthy males.

Objective: Spectral analyses of laser-Doppler flowmetry measures enable a simple and non-invasive method to investigate mechanisms regulating skin blood flow. We assessed within-day and day-to-day variability of cutaneous spectral analyses.

Methods: Eleven young, healthy males were tested twice in three identical sessions, with 19 to 24 days between visits, for a total of six tests.

The effects of local muscle temperature on force variability.

Purpose: Force variability is affected by environmental temperature, but whether the changes are from altered muscle temperature or proprioception are unclear. We tested how forearm muscle warming and cooling affected a force tracking task.

Methods: Twelve males and four females completed evoked, maximal, and isometric wrist flexion contractions (0-30% maximal) during thermoneutral-, warm-, and cold-muscle conditions.

Effect of passive heat exposure on cardiac autonomic function in healthy children.

Purpose: The aim of this study was to examine the effect of passive heat stress on heart rate variability parameters in healthy children.

Method: Fifteen children (9.3 ± 1.

Core and skin temperature influences on the surface electromyographic responses to an isometric force and position task.

The large body of work demonstrating hyperthermic impairment of neuromuscular function has utilized maximal isometric contractions, but extrapolating these findings to whole-body exercise and submaximal, dynamic contractions may be problematic. We isolated and compared core and skin temperature influences on an isometric force task versus a position task requiring dynamic maintenance of joint angle. Surface electromyography (sEMG) was measured on the flexor carpi radialis at 60% of baseline maximal voluntary contraction while either pushing against a rigid restraint (force task) or while maintaining a constant wrist angle and supporting an equivalent inertial load (position task).

Cutaneous neural activity and endothelial involvement in cold-induced vasodilatation.

Whether sympathetic withdrawal or endothelial dilators such as nitric oxide (NO) contributes to cold-induced vasodilation (CIVD) events is unclear. We measured blood flow and finger skin temperature (T) of the index finger in nine participants during hand immersion in a water bath at 35 °C for 30 min, then at 8 °C for 30 min. Data were binned into 10 s averages for the entire 60 min protocol for laser-Doppler flux (LDF) and T.

Ischemia-reperfusion injury alters skin microvascular responses to local heating of the index finger.

Background: Ischemia-reperfusion (IR) injury impairs microcirculatory function by reducing nitric oxide (NO) bioavailability and increasing sympathetic tone. This study non-invasively examined the effects of acute upper limb IR injury on local thermal hyperemia (LTH) in glabrous and non-glabrous finger skin.

Materials And Methods: In ten healthy males, LTH was examined twice (~7-10 d apart) for each skin type on the index finger using laser-Doppler flowmetry in a counterbalanced design with either 1) 20 min ischemia, followed by reperfusion (ISCH) or 2) time-matched control (SHAM).

The effects of local forearm muscle cooling on motor unit properties.

Purpose: Muscle cooling impairs maximal force. Using needle electromyography (EMG) to assess motor unit properties during muscle cooling, is limited and equivocal. Therefore, we aimed to determine the impact of local muscle cooling on motor unit firing properties using surface EMG decomposition.

The Effects of Hyperoxia on Sea-Level Exercise Performance, Training, and Recovery: A Meta-Analysis.

Background: Acute exercise performance can be limited by arterial hypoxemia, such that hyperoxia may be an ergogenic aid by increasing tissue oxygen availability. Hyperoxia during a single bout of exercise performance has been examined using many test modalities, including time trials (TTs), time to exhaustion (TTE), graded exercise tests (GXTs), and dynamic muscle function tests. Hyperoxia has also been used as a long-term training stimulus or a recovery intervention between bouts of exercise.

Effect of sympathetic nerve blockade on low-frequency oscillations of forearm and leg skin blood flow in healthy humans.

Objective: To Examine the effect of inhibiting sympathetic function on cutaneous vasomotion in the forearm and leg.

Methods: Intradermal microdialysis fibers were placed in the forearm and leg, one as an untreated control (lactated Ringer's) and the other perfused with bretylium tosylate to block sympathetic nerves. Skin blood flow was monitored using laser Doppler flowmetry.

Effect of age on cutaneous vasomotor responses during local skin heating.

This study examined the effect of ageing on the low-frequency oscillations (vasomotion) of skin blood flow in response to local heating (LH). Skin blood flow was assessed by laser-Doppler flowmetry on the forearm at rest (33°C) and in response to LH of the skin to both 42°C and 44°C in 14 young (24±1years) and 14 older (64±1years) participants. Vasomotion was analyzed using a wavelet transform to investigate power of the frequency intervals associated with endothelial, neural, myogenic, respiratory, and cardiac activities of the laser-Doppler signal.

Spectral analysis of reflex cutaneous vasodilatation during passive heat stress.

Previous work has demonstrated that spectral analysis is a useful tool to non-invasively ascertain the mechanisms of control of the cutaneous circulation. The majority of work using spectral analysis has focused on local control mechanisms, with none examining reflex control. Skin blood flow was analysed using spectral analysis on the dorsal aspect of the forearm of 7 males and 7 females during passive heat stress, with mean forearm and local temperature at the site of measurement maintained at thermoneutral (33°C) to minimize the effect of local control mechanisms.

Investigating the roles of core and local temperature on forearm skin blood flow.

We sought to isolate the contributions of core and local temperature on forearm skin blood flow (SkBF), and to examine the interaction between local- and reflexive-mechanisms of SkBF control. Forearm SkBF was assessed using laser-Doppler flowmetry in eight males and eight females during normothermia and hyperthermia (+1.2°C rectal temperature).

The contribution of sensory nerves to the onset threshold for cutaneous vasodilatation during gradual local skin heating of the forearm and leg.

During local skin heating, the temporal onset of vasodilatation is delayed in the leg compared to the forearm, and sensory nerve blockade abolishes these differences. However, previous work using rapid skin heating did not allow for determination of sensory nerve influences on temperature thresholds for vasodilatation. Two sites were examined on both the forearm and leg, one control (CTRL), and one treated for sensory nerve blockade (EMLA).

The contribution of sensory nerves to cutaneous vasodilatation of the forearm and leg to local skin heating.

Purpose: The initial cutaneous vasodilatory response to local skin heating is larger in the forearm than the leg. While the initial vasodilatation of the forearm to local heating is primarily dependent on sensory nerves, their role in the leg is unknown. We compared the contribution of sensory nerves in driving the cutaneous vasodilatory response of the forearm and leg to local heating using local anaesthetic (EMLA) cream.