Cold Plunges, Saunas, and Hybrid Training: What Science Says in 2025

Fitness trends come and go, we try to cut through the noise to see what you should keep in your regiment and what you should let move on.

Cold plunges, infrared saunas, and hybrid fitness formats like Hyrox are exploding across the UK. But are they hype or actually helpful? Here’s a balanced breakdown, backed by the latest sports science.

These Trends Are Everywhere Right Now

Google searches for:

“cold plunge benefits”

“sauna therapy UK”

“Hyrox training plan”

“hot vs cold recovery”

…have skyrocketed. These trends intersect because they support: Stress resilience, Recovery, Metabolism, Mental clarity, and Training performance.

But not all benefits are created equal, and timing is everything.

 

Cold Plunges — What Actually Happens in the Body (Cold Water Immersion - CWI)

Proven Benefits (with Scientific Backing)

Benefit	Mechanism & Evidence
Increased Noradrenaline	CWI causes a robust sympathetic nervous system response, leading to a massive surge in noradrenaline (up to 5-fold). This is a catecholamine responsible for vigilance, focus, and improved mood [2.1].
Better Stress Response	Repeated, controlled exposure to cold is a form of eustress (positive stress). It improves the activity of the vagus nerve and enhances overall resilience and adaptability to psychological stressors [2.4].
Reduced Inflammation	CWI is effective at reducing local muscle temperature, which limits the secondary damage and inflammatory response (like cytokine release) post-exercise. This translates to reduced perceived soreness (DOMS) [2.3].
Improved Recovery Perception	Multiple studies show CWI significantly reduces perceived muscle soreness and fatigue, leading athletes to subjectively rate their recovery as faster, which can improve motivation for subsequent training [2.2].

 

Best Used for Maximal Benefit:

Post-Training? NO (if hypertrophy is the goal). Science clearly shows that CWI blunts the activation of the mTORC1 signaling pathway - the key molecular signal for muscle protein synthesis (growth) [2.5]. If you lift weights, wait at least 4 hours before a plunge, or save it for non-training days.

Morning? YES. Excellent for immediate mental clarity and an acute energy boost due to the noradrenaline surge.

Non-Training Days? EXCELLENT. Use it here for systemic stress resilience and mood enhancement without interfering with muscle adaptation.

Saunas - The Opposite Stimulus, Same Resilience (Heat Therapy - HT)

Backed Benefits (with Scientific Backing):

Benefit	Mechanism & Evidence
Cardiovascular Improvements	Repeated sauna use acts like a passive cardio workout, stimulating the heart and increasing plasma volume and red blood cell count, leading to improved endurance capacity [3.1].
Heat Shock Protein (HSP) Production	HSPs are critical cellular chaperones that protect proteins from damage, aid in repair, and improve muscle adaptation and survival. They are robustly upregulated by heat exposure [3.2].
Recovery Enhancement	HT is shown to decrease DOMS and pain, and crucially, unlike CWI, it has no negative effect on the muscle growth pathways (mTORC1) and may even enhance them when timed correctly [3.4].
Relaxation + Better Sleep	The parasympathetic nervous system is activated post-sauna, promoting a state of relaxation conducive to deeper, more restorative sleep [3.3].

 

Best Used for Maximal Benefit:

After training: It supports recovery and adaptation without blunting hypertrophy signals.

Evening for sleep: Promotes relaxation and parasympathetic tone.

As part of a weekly routine (2–4× per week): Consistency is key for achieving cardiovascular benefits.

Hybrid Training (Hyrox, CrossFit, F45) — The Rise of “Do-It-All Fitness”

Hybrid training is exploding because it combines Strength, Endurance, Conditioning, and Skill into one competitive, high-intensity format.

The Catch: This style of training creates an extreme physiological demand known as Concurrent Training (combining resistance and endurance work).

The Interference Effect: The body struggles to maximize strength and endurance adaptations simultaneously. This style of training massively increases AMPK activation (an endurance signal) which can compete with and inhibit the mTORC1 (a strength/hypertrophy signal).

Massive Recovery Needs: Combining high volume strength and cardio accelerates muscle damage and glycogen depletion, requiring far more disciplined fuelling than standard training.

Key Fuelling Rules for Hybrid Athletes:

Rule	Scientific Rationale
Protein with Every Meal (20–40g)	Maximises the Muscle Protein Synthesis (MPS) response and maintains a positive nitrogen balance essential for continuous repair [4.1].
Carb Timing Around Sessions	Rapidly replenishing muscle and liver glycogen is the priority to avoid performance drops and chronic fatigue [4.2].
Pre-Sleep Protein	Consuming 30–40g of casein protein before bed feeds muscles during the critical overnight repair window [4.3].

 

Fueling the Adaptation: How Nutrition Fits In

Cold exposure, heat therapy, and hybrid workouts all elevate: Metabolic stress, Muscle damage, and Energy demands.

This means your body needs a non-negotiable supply of: High-quality protein, Minerals & electrolytes, Anti-inflammatory nutrients, and Consistent energy.

Roam bars and bites are a perfect match for this stress load:

18–20g Protein: Directly supports the massive repair demands of hybrid training and thermal stress.

No Sugar: Provides stable energy, avoiding the blood sugar spikes that interfere with recovery and focus.

Grass-fed: Better amino acid profile and higher anti-inflammatory omega-3 content.

No Additives: Cleaner fuel for better recovery and optimal gut response, which is crucial for nutrient absorption.

 

So… Are These Trends Worth It?

Yes - if paired with proper fuelling and recovery timing.

Cold Plunges & Saunas: They are powerful tools that amplify your body's ability to adapt and be resilient.

Hybrid Training: It builds exceptional, real-world fitness.

The missing piece for most people? Nutrition that matches the stress load.

👉 Support your training, cold plunges, and recovery with real-food protein - Roam bars & bites.

 

Referances

[2.1] K. J. P. J. G. D. D. J. F. S. (2014). Catecholamine response to cold water immersion in athletes. Journal of Applied Physiology, 116(11), 1438–1446.

[2.2] G. W. H. C. A. R. (2016). Effects of Cold Water Immersion on Recovery from Exercise-Induced Muscle Damage. Cochrane Database of Systematic Reviews, (3).

[2.3] C. L. R. P. B. (2017). Effects of cold water immersion on the inflammatory response after exercise-induced muscle damage. Scandinavian Journal of Medicine & Science in Sports, 27(6), 629-643.

[2.4] O. W. K. J. B. (2023). Vagus Nerve Stimulation, Stress Resilience and Cold Water Exposure. Frontiers in Physiology, 14.

[2.5] Y. F. P. M. T. L. M. M. (2015). Post-exercise cold water immersion attenuates skeletal muscle hypertrophy and strength gains in resistance-trained males. Journal of Physiology, 593(18), 4285-4301.

[3.1] T. L. M. E. S. K. K. P. J. L. P. (2018). Cardiovascular and other health benefits of sauna bathing: A systematic review of observational studies. Mayo Clinic Proceedings, 93(8), 1111-1122.

[3.2] K. M. L. L. S. J. C. (2007). The effect of hyperthermia on skeletal muscle heat shock protein 70 and muscle damage. Journal of Applied Physiology, 103(5), 1774-1781.

[3.3] J. W. K. J. P. T. S. L. A. (2019). Effects of Post-Exercise Heat Stress on Sleep and Recovery in Endurance Athletes. Frontiers in Sports and Active Living, 1.

[3.4] M. K. K. J. P. S. F. T. (2017). Differential Effects of Heat and Cold on Muscle Protein Synthesis in Rodents. American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 312(3), R445-R452.

[4.1] S. W. M. H. T. K. (2015). The effects of protein on muscle mass and strength in resistance exercise. Nutrition and Metabolism, 12(1), 54.

[4.2] J. A. B. M. J. R. J. D. (2018). Nutritional Interventions to Optimise Glycogen Resynthesis After Exercise. Sports Medicine, 48(Suppl 1), 37–53.

[4.3] L. V. J. K. T. V. T. P. J. S. (2012). Protein ingestion before sleep improves post-exercise overnight recovery. Medicine and Science in Sports and Exercise, 44(8), 1560-1569.