Table1_Moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions differently affects muscle contractile function in young males.docx

Background: We investigated the impact of moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions (CWI) on muscle force and contractility in unfatigued state and during the development of fatigue resulting from electrically induced contractions.Methods: Twelve young males participated in this study consisting of two phases [single phase (SP) followed by intermittent/prolonged phase (IPP)], with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and cold-water immersions (10°C). SP-CWI included one 45 min-bath (from 15 to 60 min). IPP-CWI included three baths (45 min-bath from 15 to 60 min, and 15 min-baths from 165 to 180 min and from 255 to 270 min), with participants sitting at room temperature the rest of the time until 300 min. Blood pressure and intramuscular (Tmu) temperature were assessed, and neuromuscular testing was performed at baseline and 60 min after baseline during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations) was performed after the last neuromuscular testing of each trial.Results: In unfatigued state, SP-CWI and IPP-CWI reduced electrically induced torque at 100 Hz (P100) but not at 20 Hz (P20), and increased P20/P100 ratio. The changes from baseline for P100 and P20/P100 ratio were lower in IPP-CWI than SP-CWI. Both cold-water immersion conditions slowed down muscle contraction and relaxation, and reduced maximal isokinetic contraction torque, but the changes from baseline were lower after IPP-CWI than SP-CWI. cold-water immersions did not impair maximal voluntary isometric contraction. During the fatiguing protocol, torque fatigue index and the changes in muscle contractile properties were larger after IPP-CWI than SP-CWI, but were in the same range as after CON conditions. The differences of muscle contractile function between SP-CWI and IPP-CWI were accompanied by a lower reduction of superficial Tmu and a smaller increase in systolic blood pressure after IPP-CWI than SP-CWI.Conclusion: IPP-CWI induces a less pronounced fast-to-slow contractile transition compared to SP-CWI, and this may result from the reduced vasoconstriction response and enhanced blood perfusion of the superficial muscle vessels, which could ultimately limit the reduction of superficial Tmu.</p

Image1_Passive heating-induced changes in muscle contractile function are not further augmented by prolonged exposure in young males experiencing moderate thermal stress.tif

Background: We investigated the impact of 1) passive heating (PH) induced by single and intermittent/prolonged hot-water immersion (HWI) and 2) the duration of PH, on muscle contractile function under the unfatigued state, and during the development of muscle fatigue.Methods: Twelve young males volunteered for this study consisting of two phases: single phase (SP) followed by intermittent/prolonged phase (IPP), with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and HWI (44–45°C; water up to the waist level). SP-HWI included one continuous 45-min bath (from 15 to 60 min). IPP-HWI included an initial 45-min bath (from 15 to 60 min) followed by eight additional 15-min baths interspaced with 15-min breaks at room temperature between 75 and 300 min. Intramuscular (Tmu; measured in the vastus lateralis muscle) and rectal (Trec) temperatures were determined. Neuromuscular testing (performed in the knee extensors and flexors) was performed at baseline and 60 min later during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations of the knee extensors) was performed after the last neuromuscular testing of each trial.Results: HWI increased Tmu and Trec to 38°C–38.5°C (p Conclusion: PH induces changes in muscle contractile function which are not augmented by prolonged exposure when thermal stress is moderate.</p

Image1_Moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions differently affects muscle contractile function in young males.tif

Background: We investigated the impact of moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions (CWI) on muscle force and contractility in unfatigued state and during the development of fatigue resulting from electrically induced contractions.Methods: Twelve young males participated in this study consisting of two phases [single phase (SP) followed by intermittent/prolonged phase (IPP)], with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and cold-water immersions (10°C). SP-CWI included one 45 min-bath (from 15 to 60 min). IPP-CWI included three baths (45 min-bath from 15 to 60 min, and 15 min-baths from 165 to 180 min and from 255 to 270 min), with participants sitting at room temperature the rest of the time until 300 min. Blood pressure and intramuscular (Tmu) temperature were assessed, and neuromuscular testing was performed at baseline and 60 min after baseline during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations) was performed after the last neuromuscular testing of each trial.Results: In unfatigued state, SP-CWI and IPP-CWI reduced electrically induced torque at 100 Hz (P100) but not at 20 Hz (P20), and increased P20/P100 ratio. The changes from baseline for P100 and P20/P100 ratio were lower in IPP-CWI than SP-CWI. Both cold-water immersion conditions slowed down muscle contraction and relaxation, and reduced maximal isokinetic contraction torque, but the changes from baseline were lower after IPP-CWI than SP-CWI. cold-water immersions did not impair maximal voluntary isometric contraction. During the fatiguing protocol, torque fatigue index and the changes in muscle contractile properties were larger after IPP-CWI than SP-CWI, but were in the same range as after CON conditions. The differences of muscle contractile function between SP-CWI and IPP-CWI were accompanied by a lower reduction of superficial Tmu and a smaller increase in systolic blood pressure after IPP-CWI than SP-CWI.Conclusion: IPP-CWI induces a less pronounced fast-to-slow contractile transition compared to SP-CWI, and this may result from the reduced vasoconstriction response and enhanced blood perfusion of the superficial muscle vessels, which could ultimately limit the reduction of superficial Tmu.</p

Research design.

<p>BS – blood samples, T_re – rectal temperature, T_mu – muscle temperature, T_sk – skin temperature. Cognitive function (CF) testing involved the unpredictable task switching test (executive function), the forward digit-span task test (short term memory), and the forced-choice recognition memory test (short term spatial recognition). Neuromuscular (NM) testing involved evaluation of spinal (H-reflexes, M-waves) and supraspinal (V-waves) excitability, evaluation of muscle contractility characteristics induced by a 1-s electrical stimulation at 1 Hz, 20 Hz, 100 Hz and TT-100 Hz; evaluation of maximal voluntary contraction torque and central activation of exercising muscle was performed with a TT-100 Hz superimposed stimulation on the maximal voluntary contraction. Intermittent head-out immersion in bath water at 14°C continued until the rectal temperature decreased to 35.5°C or until 170 min total (120 min maximum total immersion time), at which time the immersion ended regardless of the rectal temperature.</p

Subjective sensation rating (in points) during passive body cooling.

<p>n.s. P>0.05, non-significant between fast cooling (FC) and slow cooling (SC) groups. Values are means ± SD.</p><p>Subjective sensation rating (in points) during passive body cooling.</p

The blood variables before and after body cooling.

<p>*P<0.05, compared with before;</p>#<p>P<0.05, between fast cooling (FC) and slow cooling (SC) groups. Values are means ± SD.</p><p>The blood variables before and after body cooling.</p

Changes in supraspinal (V-wave) response before and after body cooling.

<p>* P<0.05, compared with before. Fast cooling group (FC); Slow cooling group (SC).Values are means ± SD.</p

VO₂, metabolic heat production and metabolic shivering before and during body cooling.

<p>*P<0.05, compared with before;</p>#<p>P<0.05 between fast cooling (FC) and slow cooling (SC) groups. Values are means ± SD.</p><p>VO₂, metabolic heat production and metabolic shivering before and during body cooling.</p

Hyperventilation throughout cold acclimation.

<p>* <i>P</i><0.05, compared with CA-1. Values are means ± SEM.</p

Body temperature, heart rate (HR), metabolic heat production (MHP), oxygen consumption (VO₂) and cold-strain index (CSI) before and after body cooling in the CA-1, CA-16 and CA-17 sessions.

<p>*<i>P</i><0.05, compared with before cooling;</p>#<p><i>P</i><0.05, compared with the CA-1 session;</p>†<p><i>P</i><0.05 – compared with the CA-16 session.</p><p>Δ  =  mean difference between before and after cold exposure. Values are means ± SEM.</p