Mineral-Infused Clothing for Recovery From Muscle Soreness and Muscle Damage After Exercise

Unaccustomed exercise with a substantial eccentric component produces exercise-induced muscle damage, characterised by a transient loss of muscle force, delayed onset muscle soreness (DOMS) that typically peaks 48 to 72 hours after exercise, reduced explosive performance and a rise in circulating creatine kinase. Lower-limb garments are widely used to aid recovery, and meta-analyses of compression garments report small to moderate benefits for strength, power and perceived soreness. Mineral-infused textiles, marketed as re-emitting body heat as far-infrared radiation, form a poorly characterised category of recovery garment, and their effect on recovery from muscle-damaging exercise is unknown.

Design: single-site, randomised, double-blind, sham-controlled, parallel-group trial with 1:1 allocation, conducted at a StudySetGo study site in Exeter, United Kingdom. Randomisation uses computer-generated permuted blocks of varying size, stratified by sex. The control garment is manufactured to the same external specification, fabric, colour, sizing and finish as the active garment but without the mineral infusion, and is supplied in identical coded packaging.

Procedures: screening and consent are completed remotely (electronic consent and screening questionnaire via PandaDoc, followed by a Zoom screening call). On Day 1, participants are randomised and issued their garments, then complete baseline assessments in a fixed order: capillary blood sample, soreness visual analogue scale (100 mm, during a bodyweight squat), maximal voluntary isometric contraction (MVC) of the knee extensors of the dominant limb and squat jump. Participants then perform a muscle-damaging protocol of 100 drop jumps (5 sets of 20, 10 s between jumps, 2 min between sets) under one-to-one supervision, followed by 0-hour assessments. Garments are worn for a minimum of 16 hours per day (approximately 8 hours waking and 8 hours overnight) through the 72-hour recovery period, removed only for assessments and personal care, and wear is recorded in a daily log. Assessments are repeated at 24, 48 and 72 hours. Participants keep their habitual diet and caffeine intake, have their last meal and any caffeine at least 2 hours before testing, attend at the same time of day (plus or minus 1 hour) on each visit, and avoid alcohol, other recovery modalities, anti-inflammatory medication and strenuous exercise during the study. A Study Exit Questionnaire at 72 hours records garment comfort and tolerability and the participant's guess of allocation.

Sample size: based on Hill et al. (2017), a difference of 8.7 percentage points in MVC recovery at 72 hours (Cohen's d = 0.888), two-tailed alpha 0.05 and power 0.80 require 42 participants (21 per group); allowing approximately 20% dropout, 52 participants (26 per group) will be enrolled.

Analysis: the primary analysis is on the intention-to-treat population using a linear mixed-effects model with group, timepoint and group-by-timepoint interaction as fixed effects, pre-exercise baseline as a covariate and participant as a random effect. Secondary models are additionally adjusted for sex. Pre-specified sensitivity analyses examine hormonal status, and a per-protocol analysis includes participants meeting the wear-adherence threshold (mean of at least 16 hours per day with no day below 12 hours). Creatine kinase is log-transformed and reported as geometric mean ratios.