Objective: To test the effects of hot-water immersion on the rapid force production and parameters of neuromuscular function in healthy adults. Design: Cross-sectional study. Methods: Fifteen healthy adults (24.9 ± 5.6 years; 178 ± 11.4 cm; 72.8 ± 16.2 kg) performed neuromuscular assessments before, after and ∼15 min after either 90 min of 42 • C (hot) or 36 • C (sham-condition) water immersion (lower body). Knee extensors rate of torque development (RTD) was measured during explosive voluntary contraction in the interval of 0−50 ms (RTD V50 ) and 0−150 ms (RTD V150 ) and during electrically-evoked contractions by single twitches (RTD twitch ) and low-and high-frequencies doublets (RTD 20Hz and 100Hz ). Rate of EMG rise (RER) was calculated for voluntary contractions and half-relaxation time (HRT) and electromechanical delay (EMD) was measured during single twitches. Results: After the hot-water immersion (when rectal and muscle temperature were elevated [↑1 • C and ↑2.4 • C, respectively]), RTD V50 , RTD 20Hz and RTD 100Hz significantly increased and HRT decreased when compared to baseline and sham-condition (p < 0.05). Approximately 15 min after the hot-water immersion (when muscle temperature was still higher [↑1.4 • C], but rectal temperature at baseline level), RTD V50 remained higher and RTD twitch presented higher values than baseline and sham-condition. The RTD 20Hz and RTD 100Hz showed further increases compared to post hot-water immersion trials. HRT showed no changes compared to post water immersion, but the EMD presented lower values than baseline and sham-condition. No changes were observed for RTD V150 and RER at any moment. Conclusion: Increased muscle temperature provoked by 42 • C hot-water immersion increases the early phase of the RTD (<70 ms) (voluntary and evoked) and decreases HRT and EMD of the knee extensors.

This study investigated the effects of high-intensity resistance training on estimates of the motor neuron persistent inward current (PIC) in older adults. Seventeen participants (68.5±2.8 years) completed a 2-week non-exercise control period followed by 6 weeks of resistance training. Surface electromyographic signals were collected using two 32-channel electrodes placed over soleus to investigate motor unit discharge rates. Paired-motor unit analysis was used to calculate delta frequency (ΔF) as an estimate of PIC amplitudes during (a) triangular-shaped contractions to 20% of maximum torque capacity, and (b) trapezoidal- and triangular-shaped contractions to 20% and 40% of maximum torque capacity, respectively, to understand their ability to modulate PICs as contraction intensity increases. Maximal strength and functional capacity tests were also assessed. For the 20% triangular-shaped contractions, ΔF (0.58-0.87 pps; p≤0.015) and peak discharge rates (0.78-0.99 pps; p≤0.005) increased after training, indicating increased PIC amplitude. PIC modulation also improved after training. During the control period, mean ΔF differences between 20% trapezoidal- and 40% triangular-shaped contractions were 0.09-0.18 pps (p=0.448 and 0.109, respectively), which increased to 0.44 pps (p<0.001) after training. Also, changes in ΔF showed moderate-to-very large correlations (r=0.39-0.82) with changes in peak discharge rates and broad measures of motor function. Our findings indicate that increased motor neuron excitability is a potential mechanism underpinning training-induced improvements in motor neuron discharge rate, strength, and motor function in older adults. This increased excitability is likely mediated by enhanced PIC amplitudes, which are larger at higher contraction intensities.

No abstract

No abstract

DOI: http://dx.doi.org/10.5007/1980-0037.2016v18n3p322 The purpose of the present investigation was to identify the effects of a 130-km cycling race on indices of biochemical indirect markers of muscle damage and muscle soreness responses during a 72-hour recovery period. Fifteen endurance-trained male cyclists which were competing for more than 2 years and were involved in systematic training at least of 3 days/wk underwent a collection of indirect biochemical markers of muscle damage (CK, LDH, Myo) and delayed onset of muscle soreness (DOMS), at five different moments of data collection: before (PRE) and immediately after (POST) a 130-km cycling race, and 24, 48, 72 hours following the cycling race. CK and LDH plasma concentrations significantly increased POST-race (p < 0.001) and remained high throughout the 72 hour recover period (CK: p < 0.05; LDH: p < 0.001). Myo increased significantly POST-race (p < 0.001) and returned to the PRE-race values 24 hours thereafter (p < 0.05). DOMS increased significantly POST-race (p < 0.001) and returned to the PRE-race values at 48 hours after (p > 0.05). A 130-km cycling race has a noteworty effect on indices of biochemical indirect markers of muscle damage and muscle soreness responses, indicating that 72 hour recovery period do not seems to be enough for long-distance cyclist, and reinforce the propositions of scientific literature about the need of a sufficient recovery period for cycling endurance athletes.

No abstract

Declines in muscle force, power, and contractile function can be observed in older adults, clinical populations, inactive individuals, and injured athletes. Passive heating exposure (e.g., hot baths, sauna, or heated garments) has been used for health purposes, including skeletal muscle treatment. An acute increase in muscle temperature by passive heating can increase the voluntary rate of force development and electrically evoked contraction properties (i.e., time to peak twitch torque, half-relation time, and electromechanical delay). The improvements in the rate of force development and evoked contraction assessments with increased muscle temperature after passive heating reveal peripheral mechanisms’ potential role in enhancing muscle contraction. This review aimed to summarise, discuss, and highlight the potential role of an acute passive heating stimulus on skeletal muscle cells to improve contractile function. These mechanisms include increased calcium kinetics (release/reuptake), calcium sensitivity, and increased intramuscular fluid.

No abstract