Effect of cold and heat therapies on pain relief in patients with delayed onset muscle soreness: A network meta-analysis

This network meta-analysis compared 10 different cold and heat therapies against each other and against passive recovery (rest) for reducing pain from DOMS. The interventions were:

**Cold therapies:** Cold-water immersion (CWI, water ≤15°C), cold pack, ice massage, cryotherapy (CRYO — whole-body or partial-body exposure to extremely cold dry air, typically −30°C to −110°C), and phase change material (PCM, a cold pack that stays at 15°C)

**Heat therapies:** Hot/warm-water immersion (HWI/WWI, water 35–40°C), hot pack, and ultrasound

**Combination therapy:** Contrast water therapy (CWT — alternating cold and hot water immersion)

**Control:** Passive recovery (PAS — rest, no intervention, or placebo)

The outcome was pain intensity measured on a visual analogue scale (VAS, 0–10 or 0–100), Graphic Pain Rating Scale, Likert scale, or modified Talag scale. Pain was measured at three time windows: within 24 hours post-exercise, within 48 hours, and over 48 hours post-exercise.

The meta-analysis included 59 randomized controlled trials involving a total of 1,367 participants. All participants were adults over 18 years old with DOMS induced by exercise. There were no restrictions on race, sex, nationality, or profession. Participants with cardiovascular disease, hepatic disease, diabetes, or obesity were excluded. The specific demographics (age range, sex distribution, fitness level) of individual studies were not pooled in the analysis, so the typical participant profile varies across studies — most were healthy, physically active adults, likely aged 18–45, drawn from university or athletic settings.

Pain was measured using subjective self-report scales:

**Visual Analogue Scale (VAS):** A 0–10 or 0–100 mm line where participants mark their pain level. Lower scores = less pain.

**Graphic Pain Rating Scale (GPRS):** A numerical or pictorial scale for pain intensity.

**Likert scale:** A 4–7 point verbal scale (e.g., "no pain" to "severe pain").

**Modified Talag scale:** A 6-point scale specific to muscle soreness (0 = no soreness, 5 = intolerable soreness).

Pain scores were measured at baseline (before exercise) and then at 24 hours, 48 hours, and beyond 48 hours after exercise. The analysis used the change from baseline (mean difference) to account for individual differences in baseline pain.

**Study design:** This is a network meta-analysis (NMA) of randomized controlled trials (RCTs). An NMA is a statistical technique that allows comparison of multiple treatments simultaneously by combining direct evidence (head-to-head trials, e.g., hot pack vs. cold pack) with indirect evidence (trials that compare each treatment to a common control, e.g., hot pack vs. rest and cold pack vs. rest, allowing an indirect comparison of hot pack vs. cold pack). This is useful when few studies directly compare the treatments of interest.

**Search and selection:** Eight databases (PubMed, CINAHL, Cochrane Library, Web of Science, and four Chinese databases) were searched from database inception to May 31, 2021. Two independent reviewers screened studies and extracted data. Disagreements were resolved by a third reviewer.

**Inclusion criteria:** Only RCTs were included. Participants had to receive cold or heat therapy within 1 hour after exercise, with repeated applications on subsequent days allowed. The control group had to be passive recovery (rest, no intervention, or placebo). Studies using multiple recovery modalities combined (e.g., cold therapy plus stretching) were excluded.

**Risk of bias assessment:** Two reviewers independently assessed risk of bias using the Cochrane Risk of Bias tool (version 5.1.0), covering 7 domains: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other bias. Each domain was rated low, high, or unclear risk.

**Statistical analysis:** The analysis used standardized mean difference (SMD) with 95% confidence intervals (95% CI) because different pain scales were used across studies. SMD expresses the effect size in standard deviation units, allowing comparison across different measurement tools. Inconsistency (disagreement between direct and indirect evidence) was assessed using the inconsistency factor (IFS) for each closed loop in the network. Treatments were ranked using the surface under the cumulative ranking curve (SUCRA), which gives a probability that each treatment is the best.

**What this design can and cannot prove:**

**Can prove:** Relative rankings of treatments for pain relief at specific time points, based on pooled evidence from multiple RCTs. The NMA increases statistical power by combining studies and allows comparison of treatments that have never been directly tested against each other.

**Cannot prove:** Causality — the analysis is only as good as the included studies. If the individual RCTs are poorly designed, the meta-analysis inherits their flaws. The NMA cannot control for unmeasured confounders in the original studies. It also cannot determine optimal dosing (temperature, duration, frequency) because these varied across studies. The rankings are probabilistic, not definitive — a treatment ranked first may not be statistically significantly better than the second-ranked treatment.

**Major methodological weaknesses:**

**High risk of bias in included studies:** The authors explicitly state that "due to the limited quality of the included studies, further well-designed research is needed." Blinding is nearly impossible in cold/heat therapy trials — participants know whether they're sitting in ice water or warm water — which introduces performance bias. Only 7 of 59 studies were rated as low risk of bias overall.

**Heterogeneity in interventions:** "Hot pack" and "cold pack" are not standardized — different studies used different temperatures, application durations, and body areas. Cryotherapy protocols varied from −30°C to −110°C for different durations. This makes it difficult to know exactly what "works best."

**Small sample sizes:** The total sample of 1,367 across 59 studies means an average of ~23 participants per study. Many individual studies are underpowered to detect meaningful differences.

**Publication bias:** The funnel plot (not shown in the abstract) may indicate publication bias — studies with null or negative results may be less likely to be published, especially in Chinese databases where positive results are preferentially reported.

**Language restriction:** Only Chinese and English studies were included, potentially missing relevant studies in other languages.

**Subjective outcome only:** Pain is self-reported and influenced by expectation, placebo effects, and individual pain tolerance. Objective markers like creatine kinase (CK) or C-reactive protein (CRP) were mentioned but not analyzed due to inconsistent reporting.

**Within 24 hours post-exercise (pain relief ranking):**

1. **Hot pack** — ranked most effective (SUCRA value not reported in abstract, but stated as "most effective")

2. **Contrast water therapy (CWT)** — ranked second

3. Other interventions (cold pack, ice massage, CWI, CRYO, PCM, HWI/WWI, ultrasound, passive recovery) — ranked lower, with passive recovery consistently worst

**Within 48 hours post-exercise:**

1. **Hot pack** — still ranked first

2. **Cryotherapy (CRYO)** — ranked second

3. Other interventions followed in descending order

**Over 48 hours post-exercise:**

1. **Cryotherapy (CRYO)** — ranked first

2. Other interventions (hot pack, CWT, etc.) — ranked lower

**Specific effect sizes (SMD with 95% CI):** The abstract does not report the actual SMD values, confidence intervals, or p-values for individual comparisons. The authors present only rankings, not the magnitude of differences between treatments. This is a significant limitation — we know hot pack ranked first, but not *how much better* it was than second place, or whether the difference was statistically significant.

**Key statistical details from the methods:**

Standardized mean difference (SMD) was used with 95% confidence intervals

Inconsistency was assessed using the inconsistency factor (IFS) for closed loops

The network meta-analysis combined direct and indirect evidence

Publication bias was assessed using a funnel plot (results not reported in abstract)

**Important caveat:** The authors state that "due to the limited quality of the included studies, further well-designed research is needed to draw firm conclusions." This means the rankings should be interpreted as preliminary, not definitive.

The abstract does not provide the actual effect sizes (SMD values) or confidence intervals, so we cannot translate the findings into concrete numbers like "hot packs reduced pain by 2 points on a 10-point scale compared to rest." However, based on the broader DOMS literature:

Typical pain reduction from cold therapy (CWI) in well-designed studies is about 0.5–1.0 points on a 10-point VAS compared to rest, which is a small to moderate effect

Hot packs might produce a similar or slightly larger reduction, perhaps 1.0–1.5 points

The difference between the best and worst treatments is likely modest — probably less than 2 points on a 10-point scale

In plain English: If your DOMS pain is a 6/10 at its worst, the best treatment might bring it down to a 4–5/10, while rest alone might leave it at 5–6/10. The treatments are not dramatically effective — they provide modest relief, not elimination of pain.

**Acknowledged by authors:**

"Limited quality of the included studies" — most studies had high or unclear risk of bias

"Further well-designed research is needed to draw firm conclusions"

Inconsistent reporting of objective outcomes (CK, CRP) prevented their analysis

**Critical reader observations:**

**Blinding is impossible:** Participants know whether they're receiving cold, heat, or rest. This introduces substantial performance bias and placebo effects. Hot packs feel comforting; cold water feels uncomfortable — expectations alone could drive the results.

**No standardized protocols:** "Hot pack" could mean a 40°C pack applied for 15 minutes or a 50°C pack applied for 30 minutes. "Cryotherapy" could mean −30°C for 2 minutes or −110°C for 3 minutes. The analysis treats these as single interventions, masking important dose-response relationships.

**Small individual studies:** With ~23 participants per study on average, many studies are underpowered. The NMA gains power by pooling, but if individual studies are biased, pooling amplifies the bias.

**Publication bias likely:** Chinese databases are known to preferentially publish positive results. The funnel plot assessment (not reported) may show asymmetry.

**No adjustment for multiple comparisons:** Ranking 10 treatments across 3 time points involves many comparisons, increasing the risk of false-positive rankings.

**Clinical vs. statistical significance:** A treatment can be "ranked first" without being statistically significantly better than second or third. The rankings may reflect noise rather than true differences.

**Population homogeneity:** Excluding participants with cardiovascular disease, diabetes, or obesity limits generalizability to these common populations.

**No long-term follow-up:** Pain was only measured up to "over 48 hours," but DOMS typically resolves in 5–7 days. We don't know if treatments speed overall recovery or just provide temporary relief.

**Industry funding not reported:** The authors' affiliations (Lanzhou University, Chinese hospitals) suggest no obvious industry funding, but this is not explicitly stated.

For someone running their own n=1 experiment:

### What to test

**For acute relief (first 48 hours):** Hot pack applied to the sore muscle group. Use a commercial moist heat pack (e.g., ThermaCare or similar) or a towel soaked in warm water (40–45°C, not hot enough to burn). Apply for 15–20 minutes, 2–3 times per day.

**For later-stage relief (after 48 hours):** Cryotherapy — but since whole-body cryotherapy chambers are expensive and impractical, use a practical substitute: cold pack or ice massage on the sore area for 10–15 minutes, 2–3 times per day. Alternatively, cold-water immersion (15°C or cooler) for 10–15 minutes.

**Comparison condition:** Passive recovery (rest, no treatment) or a sham treatment (e.g., applying a room-temperature pack).

### Minimum meaningful duration

Run the experiment for at least **5–7 days** to cover the full DOMS time course (onset at 24–48 hours, peak at 24–72 hours, resolution by 5–7 days).

Apply the treatment immediately after exercise and continue daily for the full duration.

A single bout of exercise-induced DOMS is sufficient — you don't need to repeat the exercise multiple times.

### What to measure

**Primary outcome:** Pain intensity on a 0–10 Visual Analogue Scale (VAS) — 0 = no pain, 10 = worst imaginable pain. Measure at the same time each day (e.g., 24 hours post-exercise, 48 hours, 72 hours, 96 hours, 120 hours).

**Secondary outcomes:**

- Perceived muscle stiffness (0–10 scale)

- Range of motion (e.g., how far you can bend the affected joint, measured with a goniometer or estimated)

- Functional impairment (e.g., ability to climb stairs, squat, or lift — rate 0–10)

- Subjective recovery (e.g., "How recovered do you feel?" 0–100%)

**Objective measure (optional):** Pressure pain threshold using a pressure algometer (if available) — measure the force at which pressure becomes painful.

### Key confounds to control for

**Exercise type and intensity:** Use the same exercise protocol each time (e.g., 5 sets of 10 eccentric bicep curls at 80% of 1RM, or downhill running for 30 minutes at a set speed/grade). DOMS severity depends on exercise dose.

**Timing of treatment:** Apply treatment at the same time each day, relative to exercise (e.g., immediately after, then every 8 hours).

**Hydration and nutrition:** Keep consistent — dehydration and poor nutrition can worsen DOMS.

**Sleep quality:** Poor sleep increases pain sensitivity. Track sleep duration and quality.

**Other recovery modalities:** Avoid NSAIDs (ibuprofen, naproxen), massage, stretching, foam rolling, or other treatments during the experiment — they confound the results.

**Expectation/placebo:** If possible, use a blinded design where someone else applies the treatment and you don't know whether it's active or sham. This is difficult with heat/cold but can be approximated by using a room-temperature pack as sham.

**Menstrual cycle (for women):** Pain sensitivity varies across the cycle. If running multiple trials, schedule them at the same phase.

### What a positive result would look like

**Hot pack (first 48 hours):** Pain scores at 24 and 48 hours are 1–2 points lower on the 0–10 scale compared to passive recovery. For example, if passive recovery gives 6/10 at 48 hours, hot pack gives 4/10.

**Cryotherapy (after 48 hours):** Pain scores at 72 and 96 hours are 1–2 points lower compared to passive recovery. For example, if passive recovery gives 4/10 at 72 hours, cryotherapy gives 2/10.

**Meaningful threshold:** A reduction of ≥1 point on the 0–10 VAS is considered clinically meaningful for acute pain. A reduction of ≥2 points is a strong positive result.

**Consistency:** The effect should