TLDR: Both work. They just do slightly different things.
Before a workout, light primes the muscles for performance. After, it supports recovery. The few studies that have directly compared the two windows found that both reduce muscle damage equally, but pre-exercise has a performance edge that post-exercise doesn't.9 The real answer depends on what you're optimizing for.
Before: performance and endurance
A 2024 meta-analysis pooled 34 randomized controlled trials and found that red and near-infrared light applied before exercise improved muscle endurance and significantly reduced muscle damage markers.1
Trained athletes showed the strongest response. The more you're already pushing your body, the more the pre-exercise window seems to matter.
The working theory: light primes the mitochondria before the stress hits. Think of it like warming up an engine. When the muscle has to perform, it's already running more efficiently, producing energy faster and generating less of the waste products that cause soreness and inflammation afterward.
A human crossover trial on 20 men confirmed the pattern. Pre-exercise light exposure improved performance on a progressive treadmill test, with longer time and more distance covered compared to placebo.2 The broader literature shows this effect isn't locked to one specific wavelength. It holds across most of the red-to-NIR spectrum.7
A dose-response trial on human quads reinforced something important: three different energy levels (135, 270, and 540 joules per leg) all produced the same work output with less fatigue compared to placebo.3 The effective window is wide. You don't need to nail a perfect protocol. You need to show up and do it. A few seconds daily beats one long session on the weekend.
After: recovery and less damage
Post-exercise light does a different job.
A 2022 study applied near-infrared LEDs after 100 drop-jumps and found that muscle damage markers at 72 hours were significantly lower in the light group. Importantly for training, the muscles still adapted to the stress.4 They took less collateral damage getting stronger, but they still got stronger. Recovery without blunting the effect of the training.
A head-to-head trial of 40 volunteers compared red and NIR light against ice after high-intensity exercise. Light outperformed cryotherapy on strength recovery and produced lower markers of both muscle damage and oxidative stress.5 Light beat ice. That's worth sharing next time someone reaches for the ice bath.
A meta-analysis of 8 RCTs backed this up at the cellular level, finding that post-exercise light therapy reduced oxidative damage to both lipids and proteins, while increasing the body's own antioxidant enzyme activity.6 The muscles are taking less damage in the first place, not just recovering faster.
A systematic review of 12 high-quality trials put it plainly: light applied to skeletal muscle enhances contractile function, prevents exercise-induced cell damage, and improves recovery.8
What we do
We use light both ways. A quick pass with the Ironforge before training, and another after if the schedule allows. The session is short enough to fit into a warm-up.
If you only have time for one, match it to your goal. Training hard today? Before. Recovering from yesterday? After.
Does red light therapy interfere with muscle growth?
No. The 2022 drop-jump study specifically tested this.4 The researchers measured whether post-exercise light therapy impaired the repeated bout effect, which is the mechanism by which muscles adapt to training stress. It did not. The muscles recovered faster but still adapted normally. You get the recovery benefit without losing the training stimulus.
Is red light therapy better than ice for recovery?
In at least one well-designed trial, yes.5 A randomized, double-blind study directly compared the two after high-intensity exercise. The light group recovered strength faster and showed lower markers of muscle damage and oxidative stress than both the ice group and placebo. One study isn't the final word, but the result was a clear signal.
References
- Li et al. "Can pre-exercise photobiomodulation improve muscle endurance and promote recovery from muscle strength and injuries in people with different activity levels? A meta-analysis of randomized controlled trials." Lasers Med Sci, 39(1):132, 2024. PMID: 38758297. 34 RCTs; pre-exercise PBM improved endurance (SMD 0.31, p < 0.01), facilitated strength recovery (SMD 0.24), reduced CK by 77.56 U/L. Strongest response in trained athletes.
- Miranda et al. "Using Pre-Exercise Photobiomodulation Therapy Combining Super-Pulsed Lasers and Light-Emitting Diodes to Improve Performance in Progressive Cardiopulmonary Exercise Tests." J Athl Train, 51(2):129-35, 2016. PMID: 26942660. Crossover RCT, n=20 untrained males. Pre-exercise superpulsed laser + LED combination improved performance on progressive cardiopulmonary treadmill test vs. placebo.
- Rossato et al. "Dose-response effect of photobiomodulation therapy on muscle performance and fatigue during a multiple-set knee extension exercise." Photobiomodul Photomed Laser Surg, 38(12):758-765, 2020. PMID: 33232629. Crossover RCT, n=18. Three PBM doses (135-540 J) all reduced fatigue vs. placebo.
- Padoin et al. "Phototherapy improves muscle recovery and does not impair repeated bout effect in plyometric exercise." J Strength Cond Res, 36(12):3301-3310, 2022. PMID: 33273302. RCT, n=28. Post-exercise NIR LED (940 nm) reduced CK at 72h (p < 0.01) without impairing adaptation.
- De Marchi et al. "Does photobiomodulation therapy is better than cryotherapy in muscle recovery after a high-intensity exercise? A randomized, double-blind, placebo-controlled clinical trial." Lasers Med Sci, 32(2):429-437, 2017. PMID: 28054262. RCT, n=40. PBM outperformed cryotherapy on MVC recovery and reduced CK and oxidative damage markers.
- De Marchi et al. "Can Photobiomodulation Therapy (PBMT) Minimize Exercise-Induced Oxidative Stress? A Systematic Review and Meta-Analysis." Antioxidants, 11(9):1671, 2022. PMID: 36139746. Meta-analysis of 8 RCTs, n=140. PBM reduced lipid damage (SMD=-0.72) and protein damage (SMD=-0.41) post-exercise, while increasing SOD antioxidant enzyme activity.
- See "Light Is Good for You. Don't Overthink It." on getchroma.co. Analysis of 9,000+ PBM studies showing positive outcomes from below 400 nm to beyond 1,000 nm.
- Borsa et al. "Does phototherapy enhance skeletal muscle contractile function and postexercise recovery? A systematic review." J Athl Train, 48(1):57-67, 2013. PMID: 23672326. 12 high-quality RCTs (PEDro ≥7) confirming PBM enhances contractile function and post-exercise recovery.
- Santos et al. "Effects of photobiomodulation applied at different times on functional performance and ergogenic response of rugby athletes." J Bodywork Mov Ther, 38, 2024. PMID: 38763575. Randomized crossover RCT, n=18 rugby athletes. Pre-exercise PBM improved intermittent sprint performance; post-exercise did not. No significant difference between timing windows for muscle damage markers.
