Effects of Electrical Stimulation on Delayed Onset Muscle Soreness (DOMS): Evidences from Laboratory and In-Field Studies

Abstract

Intense, long exercise can increase oxidative stress, leading to higher levels of inflammatory mediators and muscle damage. At the same time, fatigue has been suggested as one of the factors giving rise to delayed-onset muscle soreness (DOMS). The aim of this study was to investigate the efficacy of a specific electrical stimulation (ES) treatment (without elicited muscular contraction) on two different scenarios: in the laboratory on eleven healthy volunteers (56.45 ± 4.87 years) after upper limbs eccentric exercise (Study 1) and in the field on fourteen ultra-endurance athletes (age 47.4 ± 10.2 year) after an ultra-running race (134 km, altitude difference of 10,970 m+) by lower exercising limbs (Study 2). Subjects were randomly assigned to two experimental tasks in cross-over: Active or Sham ES treatments. The ES efficacy was assessed by monitoring the oxy-inflammation status: Reactive Oxygen Species production, total antioxidant capacity, IL-6 cytokine levels, and lactate with micro-invasive measurements (capillary blood, urine) and scales for fatigue and recovery assessments. No significant differences (p > 0.05) were found in the time course of recovery and/or pre-post-race between Sham and Active groups in both study conditions. A subjective positive role of sham stimulation (VAS scores for muscle pain assessment) was reported. In conclusion, the effectiveness of ES in treating DOMS and its effects on muscle recovery remain still unclear.

Keywords: exercise; fatigue; micro-invasive; non-contracting electrical stimulation; oxy-inflammation; pain; ultra-runners.

Figure 1

Laboratory Study (1). Experimental protocol design. As indicated, all subjects were tested at rest (T0), after exercise (T1), after electrical stimulation (ES, T2), and 1 h and 24 h post-exercise (T3 and T4). Active stimulation (red line) or Sham (blue line) were applied for 10 min at the end of the exercise. The red drops indicate the timing of the blood samples collection.

Figure 2

Elevation profile of the race (Tot Dret, TD) (http://www.tordesgeants.it (16 September 2015)) and experimental protocol adopted to measure biomarkers on the biological samples collected from the selected participants.

Figure 3

Time course of: (A) Reactive Oxygen Species (ROS) production rate (μmol.min⁻¹) calculated from the Electron Paramagnetic Resonance (EPR) spectra, (B) total antioxidant capacity (TAC; nW), (C) blood lactate concentration (La_[b]; mM), before (rest, T0), immediately after the exercise (end, T1) and after the electrical stimulation (ES = 10 min duration; T2). (D) Time course of interleukin-6 (IL-6; pg/mL) concentration at rest, at the end of the exercise and 1 h post-electrical stimulation (ES = 1 h; T3). Data were obtained during the two experimental sessions: Sham (black squares), Active (red squares) and expressed as mean ± SD. Lines are drawn as eye guide. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001 symbols show statistically significant differences.

Figure 4

(A) Borg scale at end exercise (T1); (B) time course of the VAS score; (C) maximal isometric handgrip strength (N). Data were obtained from the two groups: Sham (black squares), Active (red squares) and expressed as mean ± SD. Lines are drawn as eye guide. Statistically significant differences symbols: * p < 0.05; ** p < 0.01; **** p < 0.0001.

Figure 5

Examples of thermographic images with color-coded temperature maps; in the middle of the figure, the skin temperature (C°) data recorded at rest (T0), at the end of the exercise (end, T1) and after the electrical stimulation (T2, post-ES 10 min duration) for Sham (black squares–lines) and Active (red squares–lines) groups. Data are expressed mean ± SD. Statistically significant differences symbols: * p < 0.05; *** p < 0.001; **** p < 0.0001. At the left and right sides of the panel, anterior body infrared thermal images at T0 (A,A’), T1 (B,B’) and T2 (C,C’). All images were normalized to the same high reference level.

Figure 6

The electrical stimulation (ES) treatment effect after ultrarace (T1) on oxidative stress (OxS) is shown by the histogram plots of (A) Reactive Oxygen Species (ROS) production rate (μmol.min⁻¹), (B) Total Antioxidant Capacity (TAC; nW), (C) total glutathione (tot GSH; μM), (D) hemoglobin (Hb; g/L), (E) blood lactate concentration ([La]b; mM), and interleukin -6 (IL-6; pg · mL⁻¹) (F). Light red and light gray bars: ES_Active and ES_Sham treatments at T0; ES_Active (red bars) and ES_Sham treatments (black bars) at T1. On each bar, single data are displayed by empty circles. Data are expressed as mean ± SD. Statistically significant differences symbols: * p < 0.05, and ** p < 0.01.

Figure 7

Electrical stimulation (ES) treatment effect after ultrarace (T1) on (A) creatinine (g · L⁻¹) and (B) neopterin (μmol/min⁻¹ creatinine) obtained from urine samples in both groups. Results are expressed as mean ± SD. Light red and light gray bars: ES_Active and ES_Sham treatments at T0; ES_Active (red bars) and ES_Sham treatments (black bars) at T1. On each bar, single data are displayed by empty circles. Data are expressed as mean ± SD. Statistically significant differences symbols: * p < 0.05, and ** p < 0.01.

Figure 8

The electrical stimulation (ES) treatment effects after (T1) ultrarace on (A) Borg scale; (B) VAS and (C) TQR scores. Data are expressed mean ± SD. In light red and light gray, ES_Active and ES_Sham treatments at T0; in red ES_Active and black ES_Sham treatments at T1. Statistically significant differences symbols: * p < 0.05.