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

Abstract

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.

Keywords: cold exposure; cold habituation; cold-water immersion; muscle contractility; muscle fatigue; muscle force; temperature.

FIGURE 1

Neuromuscular testing and fatiguing protocol (A), and experimental design (B). P20, electrical stimulation at 20 Hz; P100, electrical stimulation at 100 Hz; TT, 250-ms test train stimulation at 100 Hz; MVIC, maximal voluntary isometric contraction; KE, knee extension; KF, knee flexion; BP, blood pressure; Tmu, intramuscular temperature; Trec, rectal temperature; HR, heart rate; CON, control condition; CWI, cold-water immersion condition. Fatiguing protocol consisting of 100 trains of electrical stimulation of the knee extensors (100 x 250-ms TT) was only performed after the last neuromuscular testing (i.e., second neuromuscular testing during the single phase and 5th neuromuscular testing during the intermittent/prolonged phase). *: at the time points 165 and 255 min, Tmu was only measured in the CWI condition.

FIGURE 2

Physiological measurements during the single and intermittent/prolonged phases. Heart rate (HR) (A,B), diastolic (C,E) and systolic (D,F) blood pressures (BP), rectal temperature (Trec) (G,H) and intramuscular temperature (Tmu) at three depths (1, 2, and 3 cm) (I,J) during the single and intermittent/prolonged phases, respectively. Data are shown as mean ± SD and individual values are presented in panels C–F. SP, single phase; IPP, intermittent/prolonged phase. *, p < 0.05; ***, p < 0.001: Significant differences CON vs. CWI. In I and J, significant differences are between CON and CWI are at the three depths. In J, Tmu was not assessed in CON at the time points 165 and 255 min. N = 12 for all parameters except for Tmu (N = 11) (I,J).

FIGURE 3

Electrically induced isometric torques in the unfatigued state. Peak torques at 20 Hz (P20) (A,B) and 100 Hz (P100) (C,D), and P20/P100 (E,F) during the single and intermittent/prolonged phases, respectively. Data are shown as mean ± SD and all panels include individual values. SP, single phase; IPP, intermittent/prolonged phase. *, p < 0.05; **, p < 0.01: Significant differences CON vs. CWI. N = 12.

FIGURE 4

Peak torques and contractile properties derived from a 250-ms test train stimulation at 100 Hz (TT) in the unfatigued state. TT torques (A,B), contraction time/peak torque (C,D), half-relaxation time (HRT) (E,F), peak rate of torque development (RTD) (G,H) and peak rate of torque relaxation (RTR) (I,J) during the single and intermittent/prolonged phases, respectively. Data are shown as mean ± SD and all panels include individual values. SP, single phase; IPP, intermittent/prolonged phase. *, p < 0.05; **, p < 0.01; ***, p < 0.001: Significant differences CON vs. CWI. N = 12 for all parameters except for RTD (N = 9) (G,H).

FIGURE 5

Maximal voluntary contraction torques and central activation ratio (CAR) in the unfatigued state. Maximal voluntary isometric contraction (MVIC) torques (A,B), CAR (C,D), knee extension (KE) maximal isokinetic torques (E,F), and knee flexion (KF) maximal isokinetic torques (G,H) during the single and intermittent/prolonged phases, respectively. Data are shown as mean ± SD and all panels include individual values. SP, single phase; IPP, intermittent/prolonged phase. **, p < 0.01; ***, p < 0.001: Significant differences CON vs. CWI. N = 12.

FIGURE 6

Torques and contractile properties during the fatiguing protocol. Torques during 250-ms test train stimulations at 100 Hz (TT torques) (A,B), contraction time/peak torque (C,D), half-relaxation time (HRT) (E,F), peak rate of torque development (RTD) (G,H), and peak rate of torque relaxation (RTR) (I,J) during the single and intermittent/prolonged phases, respectively. Data are shown as mean ± SD. SP, single phase; IPP, intermittent/prolonged phase. *, p < 0.05; **, p < 0.01: Significant differences CON vs. CWI. N = 12 for all parameters except for RTD (N = 10) (G,H) and RTR (N = 10) (I,J).