In this mini-review, we highlight the key mechanisms surrounding CWI and endurance exercise adaptations, reiterating the potential for CWI to enhance endurance performance, with support from classical and contemporary works.

This review also discusses the implications and insights with regards to endurance and strength adaptations gathered from recent studies examining the longer-term effects of CWI on training performance and recovery. Lastly, a periodized approach to recovery is proposed, where the use of CWI may be incorporated during competition or intensified training, whilst strategically avoiding periods following training focused on improving muscle strength or hypertrophy.

Cold water immersion CWI is a strategy aimed at enhancing recovery from strenuous exercise, typically involving the submersion up to the waist or mid-torso for ~5—20 min in temperatures between ~8 and 15°C Versey et al. Following contemporary work by Vaile et al. Complementing this growth in research, CWI has become one of the most popular post-exercise recovery strategies utilized amongst athletes during training and competition Périard et al.

Meta-analyses and experimental research in general show that CWI can beneficially influence the recovery of physical performance Montgomery et al. Nevertheless, many consider the efficacy of CWI to be equivocal. The inconsistent findings of CWI hence must be acknowledged, and this is likely driven by factors such as the nature of exercise modality preceding CWI, nature of recovery variables assessed, timing between recovery assessment and completion of CWI, and the CWI protocol itself.

While such complexities need to be resolved to appropriately compare study findings and interpret with context, recent discussions have revolved extensively around how the regular use of CWI for recovery might in parallel influence adaptations to exercise Broatch et al.

Yet, the first study to address this extends considerably back to Yamane et al. Following a hiatus, a series of studies examining the influence of CWI on adaptation to endurance exercise emerged from independent laboratories Ihsan et al. A recent meta-analytical review showed that CWI effects on exercise adaptations are mode-dependant, where resistance training adaptations were diminished, whilst aerobic exercise performance seemed unaffected Malta et al.

Alongside these publications, detailed narrative reviews on the adaptative response following regular CWI have been published within this research topic series Petersen and Fyfe, , and elsewhere Broatch et al.

Additionally, editorials, point-counterpoints, and opinion pieces Allan and Mawhinney, ; McPhee and Lightfoot, ; Méline et al.

However, potential adaptive benefits that can be harnessed from CWI following endurance exercise, or from a recovery objective are often overlooked. In this mini-review, we have adopted an introspective approach in discussing the molecular mechanisms and rationale surrounding CWI and endurance exercise adaptations.

Moreover, we review and discuss key studies which provide information on the applied scenarios where CWI can be utilized to promote physical recovery and adaptation whilst avoiding potential negative effects on hypertrophy and strength gains.

Cold stimulus is a physiological stressor capable of triggering primary signals and downstream cascades implicated in exercise-induced improvements in muscle oxidative function Ihsan et al.

Subsequent studies extended these initial findings by demonstrating comparable increases in muscle oxidative enzymes between cold acclimation and exercise Hamilton and Ferguson, ; Harri and Valtola, More recent studies have since shown improved fatigue resistance and exercise capacity following cold adaptation, in line with molecular signatures implicating increased mitochondrial content Schaeffer et al.

In summary, research within rodent models highlight cold exposure as a viable modality to enhance muscle oxidative adaptations and endurance. Seminal work by Spielgeman's group in the late 90's generated major breakthroughs in the mechanisms underpinning mitochondrial biogenesis Puigserver et al.

Their work investigating the mechanisms of adaptive thermogenesis led to the discovery of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1α PGC-1α , which was found to robustly increase in response to cold exposure 3 and 12 h exposure 4°C in mice brown fat and skeletal muscle, concomitant with an increase in numerous mitochondrial markers Puigserver et al.

Subsequent work highlighted a regulatory role for PGC-1α in mitochondrial biogenesis Lira et al. Following evidence within human exercise models demonstrating a regulatory role for PGC-1α in skeletal muscle aerobic adaptations Pilegaard et al. Whilst CWI was not conceived as a strategy specifically meant to supplement exercise adaptations, there was substantial interest in examining how recovery-based CWI might influence skeletal muscle adaptations to endurance exercise Ihsan et al.

This line of enquiry is likely motivated by work in cell cultures and rodents demonstrating robust increases in mitochondrial markers following exercise and cold exposure with common mechanisms involving PGC-1α.

Moreover, recent work in humans extends further support, where markers of mitochondrial development have been shown to be enhanced in the skeletal muscle after acute aerobic exercise in the cold compared with room temperature Shute et al. In agreement, CWI 10—15 min 8—10°C administered independently, or following an acute bout of endurance exercise was shown to increase the mRNA of PGC-1α and VEGF Ihsan et al.

However, an increase in PGC-1α protein content was not consistently observed in these studies Ihsan et al. Regardless, complimenting the aforementioned studies showing an increase in VEGF mRNA Ihsan et al. Conversely, Broatch et al. Factors such as subcutaneous fat, muscle mass, body surface area, and acclimation status may influence the adaptations that are driven by the magnitude of tissue temperature change, and hence partly account for such disparity in findings.

Collectively, these findings indicate that the effects of post-exercise CWI may be less pronounced following high-intensity exercises, but is able to influence molecular and structural adaptations befitting muscle oxidative function following lower intensity endurance exercise.

Although such molecular responses would expectedly improve endurance performance in the longer term, Yamane et al. The authors suggested that the decrease in muscle temperature and metabolism following cooling might have suppressed regenerative mechanisms mediated through inflammatory and heat shock proteins HSP.

This mechanism is unlikely prevalent during recovery-based CWI protocols resulting in mild to moderate decreases in tissue temperature. Indeed, typical post-exercise CWI involves 10—15°C immersion for 10—15 min, and such protocols have been shown to not influence skeletal muscle inflammatory response, HSP expression, or trafficking Aguiar et al.

Interestingly, HSF-1, a transcription factor for multiple HSPs, has been shown to be upregulated following regular CWI administered throughout 4 weeks of endurance training Aguiar et al. As such, the findings demonstrated by Yamane et al.

In contrast to Yamane et al. For instance, regular CWI administered during 4—6 weeks of sprint- or aerobic-interval training similarly improved maximal oxygen uptake, peak aerobic power, and time-trial performance compared to control conditions Aguiar et al.

Likewise, CWI administered to competitive cyclists undergoing weeks of intensified training reported similar improvements in most cycling performance parameters, although some parameters were reported to improve to a greater extent following CWI Halson et al.

While these findings refute suggestions that CWI might counteract endurance adaptations, it nevertheless questions whether post-exercise CWI is an effective strategy to promote muscle adaptations resulting in improved exercise performance. Indeed, changes in acute signaling response Ihsan et al. Some have reasoned that endurance performances are largely governed by central factors e.

Alternatively, frequent CWI might have de-sensitized transcriptional responses. For instance, the magnitude of PGC-1α mRNA increases have been shown to progressively diminish in response to repeated exercise stimulus Perry et al.

Similarly, PGC-1α mRNA has been shown to robustly increase following exercise in a cold environment, but demonstrated a blunted PGC-1α mRNA response to an identical stimulus following 3 weeks of endurance training in the cold Shute et al.

However, it remains to be ascertained if this attenuated response is due to habituation to cold, exercise or a combination of both stimuli. Regardless, it must be re-iterated that CWI does not appear to impair aerobic training adaptations, and can be confidently incorporated as a recovery modality following endurance training sessions.

While some studies have shown that CWI can enhance physical recovery following resistance exercise Vaile et al. Indeed, regular CWI has been shown to attenuate the magnitude of anabolic signaling Roberts et al.

Readers are directed to excellent reviews elsewhere Broatch et al. Complimenting these mechanisms, we suggest that the attenuated increase in muscle mass observed following CWI and resistance training may be part of a macro-level mechanism protecting the oxidative profile of the muscle.

This is supported by D'Souza et al. Reductions in muscle blood flow and metabolism during CWI may reduce O 2 supply and utilization Ihsan et al.

Further support for such a phenotypic response can be derived from rodent and human models of cold-acclimation. Similarly, Bae et al. While we rationalize that the dampened increase in muscle mass observed following CWI is a compensatory mechanism improving oxidative function, further research is needed to understand how this might influence athletic function and performance.

For instance, it is currently unknown if CWI influences the regulation of muscle mass following aerobic exercise, and whether this hypothetical trade-off involving the attenuated increase in muscle mass and strength might be beneficial to endurance performance.

On the other hand, co-assessment of muscle aerobic function within these resistance training studies Frohlich et al. In sports science practice, CWI is likely to be incorporated at various instances to promote recovery, particularly when recovery time between sessions is limited.

Caution should be warranted against the regular use of CWI particularly following resistance exercise sessions. These studies collectively demonstrate no impairments in strength gains despite administering frequent post-exercise CWI over 2.

In contrast to the current literature Frohlich et al. Such divergent findings are hard to reconcile. One possibility, as Broatch et al. Table 1. Summary of studies examining the longer-term effect of CWI on the recovery of exercise performance. Training frequency reported within these applied studies surmounts to at least 10 sessions per week Table 1.

Perhaps, in scenarios where recovery between training sessions may be limited, CWI can improve training performances and consequently the stimulus for adaptation. In support, post-exercise CWI has been shown to enhance the ability to perform more volitional work during subsequent squat exercise Roberts et al.

Given that adaptations to exercise stimulus are volume and intensity dependant, it seems reasonable to consider that the recovery benefits of CWI and resultant increase in training quality might outweigh its dampening effects on hypertrophy response.

Conversely, it can be argued that anabolic adaptations are better enhanced if CWI is avoided, albeit this might deter the quality of subsequent training sessions. It is currently unknown which approach would better influence athletes' recovery-adaptation interaction.

Longer term applied studies similar to those highlighted in this review Table 1 will significantly contribute to our understanding in this area. These findings show promise that beneficial recovery outcomes can be harnessed whilst avoiding negative effects of CWI on strength gains by simply avoiding the use of this recovery modality in the proximity of resistance training sessions.

Regardless, we acknowledge that these studies were not specifically designed to address this notion. Moreover, the majority of these studies were relatively short-term 2. Specific, longer-term studies are therefore required to address the effect of CWI timing on strength adaptation.

Cold water immersion is widely utilized by athletes during training and competition. Given that both a cold stimulus and exercise are independent stressors capable of enhancing muscle oxidative function, there remains substantial interest in examining how this modality might influence adaptations to exercise.

Although post-exercise CWI up-regulates mitochondrial-related signaling, longer-term changes in protein content and result in vascular adaptations, these changes do not seem to translate to improved endurance performance.

As such, further research is required to elucidate how endurance performance can be improved through its positive molecular signaling outcomes for CWI to be incorporated to enhance exercise-induced oxidative adaptations. It must be re-iterated that CWI does not impair aerobic training adaptations, and can be incorporated as a recovery modality following endurance training if needed.

In contrast, regular CWI recovery incorporated into a resistance training program will dampen strength adaptations, and therefore the use of this modality following resistance exercise sessions should be discouraged.

However, there is emerging data showing no impairments in strength gains in athletes incorporating regular use of CWI during intensified training periods; this either indicates that the recovery benefits conferred by CWI may outweigh its dampening effects on hypertrophy response, or the negative effects of CWI on strength may be circumvented by programing CWI following technical or aerobic conditioning sessions.

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Aguiar, P. Post-exercise cold water immersion does not alter high intensity interval training-induced exercise performance and Hsp72 responses, but enhances mitochondrial markers.

Cell Stress Chaperones 21, — doi: PubMed Abstract CrossRef Full Text Google Scholar. Allan, R. Is the ice bath finally melting? Cold water immersion is no greater than active recovery upon local and systemic inflammatory cellular stress in humans.

PGC-1α alternative promoter Exon 1b controls augmentation of total PGC-1α gene expression in response to cold water immersion and low glycogen availability. Postexercise cold water immersion modulates skeletal muscle PGC-1alpha mRNA expression in immersed and nonimmersed limbs: evidence of systemic regulation.

Low pre-exercise muscle glycogen availability offsets the effect of post-exercise cold water immersion in augmenting PGC-1α gene expression.

Bae, K. Muscle fibre size and capillarity in Korean diving women. Acta Physiol. A study looked at CWI as a recovery tool over 8 weeks of leg-based weight-training, with 11 participants training 3x a week.

After each session, they either spent 10 min immersed up to the neck in 15°C, or else they did a control and just rested on a couch for 10 min. They were tested before and after the 8 weeks of training, and again 3 weeks later.

On the graph we see the results for the strength and power tests at pre, post, and 3 weeks after training, with the CWI in blue and the control in white. The authors saw a slight improvement in strength and power in the control condition WITHOUT CWI. However, there was actually a trend towards slightly less strength and power over time when CWI was used!

The circumference of the thigh increased with both recovery methods. However, when using ultrasound to measure the thigh muscle itself, the CWI recovery actually led to less muscle thickness! One big improvement to this study would be if they had taken muscle samples to really look at the structural and metabolic changes in the muscle cells themselves.

However, this study is unique in being such a long study tracking CWI use. However, it may still be useful after competitions with a lot of muscle damage, as the focus then is on damage control rather than adapting to training.

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