Cold applications have been proposed to be beneficial for athletes under various circumstances (5,6,38). In particular, during recent years cold-water immersion (CWI) has been established as a promising means to support recovery in high-performance sports after highly intensive training bouts or competitions (15,17,26,40). Several studies analyzed the recovery effects of CWI, but the overall results seem to be conflicting (29). Some studies have described the beneficial effects on performance and strength development (7,8,27,35,36), whereas other studies found no or only very small positive effects (10,20–23,28). A recent meta-analysis arrived at the result that during recovery, CWI has the potential to effectively enhance strength and power performance and to reduce muscle soreness and muscle damage compared with a passive control condition. Leeder et al. (26) illustrated that CWI is an effective strategy to reduce symptoms of delayed onset muscle soreness at 24, 48, 72, and 96 hours after exercise, in particular after high-intensity or eccentric exercise. Nevertheless, the underlying physiological mechanisms remain less clear (6,39). Furthermore, CWI had no direct effect on the recovery of muscle strength, but it was effective to improve recovery of muscle power. In this context, Leeder et al. (26) pointed out that CWI has no substantial negative effects on recovery from strenuous exercise, but the knowledge about the effects of chronic cold-water application on adaptations to training is very limited. Halson (15) reviewed the scientific literature with reference to the time frame between different exercise modes (e.g., sprint, cycling, weight training, swimming) and the effectiveness of hydrotherapy for recovery. The author (15) concluded that the time frame between competitions or intense training sessions and the possible benefits and risks should be considered and that evidence-based recovery modalities should be applied. Lane and Wenger (25) examined the effects of active recovery, massage, and CWI on performance of repeated bouts of high-intensity cycling separated by 24 hours. Active recovery, massage, and CWI enhanced the recovery process between the 2 high-intensity, intermittent exercise sessions separated by 24 hours, but the effects of CWI were greater when compared with the other recovery forms. Poppendieck et al. (29) showed in a current meta-analytical review that CWI (2.9%) and cryogenic chambers (3.8%) seem to be more beneficial for sports performance than cooling packs (−1.4%). Furthermore, whole-body immersion (5.1%) was observed to be significantly more effective than partial-body CWI for only 1 leg or arms (1.1%).
Most studies on CWI for recovery analyzed short periods up to 1 week. The common situations in a high-performance setting are intensive training periods or camps that last from 2 weeks to several weeks. Although most studies focused on recovery, the adaptational aspect has been mostly neglected (21). Interestingly, Yamane et al. (41) analyzed adaptations to strength (lower arm exercises) and endurance (cycling) training lasting 4–6 weeks in untrained subjects in 4 different experiments. After each strength or endurance training session, one of the trained limbs was cooled in 5° C or 10° C, respectively, cold water, whereas the other limb was not. Endurance and strength endurance adaptations were compromised in the cooled extremity compared with the control limb, whereas maximal strength was not consistently affected in all experiments. Training-induced changes on a cellular and humoral levels and myofibrillar muscle damage are essential triggers of training adaptations. Yamane et al. (41) speculated that CWI may suppress these processes and, thus, intended training adaptations might be deteriorated when CWI is applied regularly after training (21). To our knowledge, to date, this is the only study that focused on training adaptations as a result of CWI. Untrained subjects were analyzed, and the differences between conditions were rather small. Thus, a conclusive statement is not possible yet. Because the recovery effects tend to be small as well—although these small effects are likely relevant in a high-performance setting—it seems warranted to further analyze the possible detrimental effects of cooling interventions (10).
Therefore, we conducted the present pilot study to analyze the effects of long-term applications of CWI on adaptations to strength training in already trained subjects. We hypothesized according to Howatson et al. (21) and Yamane et al. (41) that CWI will reduce training-specific adaptations in long-term training interventions.
Experimental Approach to the Problem
The study was designed as within-subject repeated-measures experiment. Each participant served as his own control. Before training and testing, 2 weeks of familiarization were performed (3 appointments for familiarization with the specific training and test protocol and with the CWI procedure). After that period, the pretest was conducted followed by the 5-week strength training period. After the posttest and a 2-week detraining period, a retention test was performed. Strength training (1-legged curl) was performed twice a week at the same time of day (Monday and Thursday or Tuesday and Friday, respectively, constant for each participant). Recovery phase between the training sessions were held constant. The participants were reminded to maintain their usual nutritional and lifestyle habits, including manual work (normal strength training routines) and sport-specific activities (e.g., running, swimming, volleyball, climbing, soccer) throughout the study period. At pretest (T1), posttest (T2), and retention test (T3), the 1 repetition maximum (RM) and the 12RM were determined according to the protocol of Baechle and Earle (2). After a warming-up with light resistance, the load was gradually increased until the athlete was able to complete just 1 (1RM) or 12 repetition(s) (12RM) with proper exercise technique. Three to 5 testing sets were allowed. Testing and training device was the same. Before all tests and training sessions, the machines were adjusted to the individual anthropometric requirements. Testing order was held constant, and all tests were conducted on the same day.
A total of 17 healthy and experienced male sport students (mean ± standard deviation age, 23.5 ± 2.4 years; range, 20–28 years; weight, 76.5 ± 8.7 kg; body fat, 13.9 ± 3.8%) participated in the present study. Strength training experience was at least 6 months (range, 6 months to 5 years). The participants typically performed 1–3 strength training sessions per week with 1–3 hours per session. All participants were thoroughly informed about the study design, risks, and possible benefits associated with the present study and provided written informed consent before participation. The study complied with ethical guidelines as outlined in the Declaration of Helsinki. Ethical approval was obtained from the local ethics committee. All training and testing sessions were conducted at the Olympiastützpunkt Rheinland-Pfalz/Saarland. Before the training or testing sessions, no strength training was allowed (24 hours) for the legs.
Strength Training Procedures
The 5-week strength training was carried out using a leg curl (gym80 International, Gelsenkirchen, Germany) with a defined movement speed (metronome-controlled, 2-second concentric and 2-second eccentric per repetition for the hamstring muscles) and a consistent range of motion in the knee joint (90° flexion and 170° extension at knee angle). Before strength training, a 5-minute warm-up was executed on a bicycle ergometer with 60–70 revolutions per minute at 150 W. In between the 3 series of each leg, a rest of 3 minutes took place during which the other leg was exercised (lifting protocol: 3 sets of 8–12 repetitions with 3 minutes of rest (14,24)). The load was set to arrive at 8–12 repetitions per series (75–80% 1RM) until exhaustion (progressive load increase during the training period) and based off the initial 1RM. If more than 13 repetitions were achieved, the load was increased for the following training session. The participants started each training session with exercising the cooled leg. The cooled and uncooled legs were randomly determined according to the pretest 1RM and to arrive at an equal distribution between the dominant leg and nondominant leg. Leg dominance was thereby defined with respect to leg strength (1RM). There was no difference in total training workload between the cooled and uncooled legs and between the dominant and the nondominant legs. The distribution was almost homogeneous (cooled leg dominant, n = 9 and cooled leg nondominant, n = 8). This assignment was held constant over the training period.
Immediately after each strength training session, a CWI was carried out for the previously defined leg. The cooling consisted of 3 4-minutes cooling intervals with a 30-second rest period in between. The other leg was not cooled (room temperature, 20–23° C). The water temperature for the CWI was 12.0 ± 1.5° C (39). To keep the water temperature as constant as possible, the water was stirred before the cooling phase. The CWI was applied to the entire leg. The test person climbed up to the iliac crest into a cooling barrel filled with ice water. The other leg was rested outside.
Data are presented as means with SDs. To analyze the time course of dependent variables during the training period, a 2-factor repeated-measures analysis of variance (ANOVA: factor time: T1 vs. T2 vs. T3; factor intervention: cooled leg vs. control leg) was calculated. In case of significant time effect, the Bonferroni post hoc test was applied. In addition, the percentage changes for both conditions from T1 to T2 and from T1 to T3, respectively, were analyzed by means of a 2-factorial ANOVA (factor time: difference between T1 and T2 vs. difference between T1 and T3, factor intervention: cooled leg vs. control leg). Partial eta square (
) was used to assess effect size with
> 0.06, and
> 0.14 indicating small, medium, and large effects, respectively (9). An α-level of p ≤ 0.05 was accepted as statistically significant. As this study had pilot character and small changes might be relevant, a p value between 0.05 and 0.1 was accepted as indicating a trend. In addition, for each variable, the percentage difference in the change scores between cooled and control leg, from T1 to T2 and T1 to T3, respectively, were calculated together with corresponding 90% confidence intervals (CI). To take potential baseline differences into account, calculations were adjusted for pretest values. A practically worthwhile change was assumed when the difference score was at least 0.2 of the between-subject standard deviation (19). The probability for an effect being practically worthwhile was additionally calculated (4). These calculations were conducted using a published spreadsheet in Microsoft Excel (Microsoft Corp., Redmond, WA, USA) (18).
We observed a significant increase in 1RM and 12RM from baseline to T2 and T3, respectively, and a further significant increase in 12RM from T2 to T3 (Table 1). In addition, we found a tendency for a “large” intervention effect with higher values for the control leg in both parameters and a “moderate” to “large” time × intervention interaction also in favor of the control leg (Table 1). The mean difference between the control leg and the cooled leg in 1RM was 0.7 kg at baseline, 2.3 kg at T2, and 2.6 kg at T3. Figure 1 displays the percentage changes from T1 to T2 and from T1 to T3 for both conditions. There was a tendency for further increases in strength from T2 and T3 for 1RM (time effect: p = 0.08) and 12RM (time effect: p = 0.06), respectively. The percentage gains in 12RM were significantly larger in the control leg (intervention effect: p = 0.01;
= 0.33). The moderately higher relative increases in the control leg for 1RM were not significant (intervention effect: p = 0.21;
The percentage change difference between the cooled and the control leg were 1.6% (90% confidence interval [CI], −2.6% to 5.7%) for the increase in 1RM from T1 to T2 and 2.0% (90% CI, −2.9% to 6.7%) from T1 to T3 in favor of the control leg. The probability for this effect to be practically relevant was 37% and 35%, respectively. The corresponding figures for 12RM were as follows: 1.1% (90% CI, −4.9% to 6.7%) for the increase in 1RM from T1 to T2 and 2.3% (90% CI, −5.5% to 7.7%) from T1 to T3 with a 40% and 37% probability for both effects to be practically relevant, respectively.
The main result of the present study was that strength training adaptations were reduced by 1–2% after a 5-week strength training regimen when the trained leg was regularly cooled directly after training compared with an uncooled control condition. The effects were rather small, and the probability of the effects to be practically relevant was below 40%. Nevertheless, this result should be considered when CWI is applied in high-performance sports to support recovery from moderate-intensive training bouts aiming for muscle hypertrophy.
Strength training in experienced sport students led to a significant performance increase of the concentric maximum strength (1RM) and the load in the 12RM test. Under regular cooling, the 1RM increased by 8.2% from the pretest to the retention test, whereas the uncooled side improved by 10.3%. The difference between the 2 conditions was 2.7% for 1RM and 1.4% for 12RM at T3. Cold-water immersion is frequently applied in sports practice to support recovery. Poppendieck et al. (29) found, in this context, an average effect of cooling on strength recovery in trained athletes of 2.4%. This is very similar to the observed differences in adaptations in the present study. Thus, the anticipated recovery effects tend to be small as well. However, such small effects might be regarded relevant in a high-performance setting. Because these considerations hold true for adaptations and recovery effects, it seems warranted to further analyze possible detrimental effects of cooling interventions. The present results are in accordance with the observations of Yamane et al. (41) who reported that CWI applied after training led to negative effects on training adaptations. Thus, although CWI seems to be a potentially beneficial means to support recovery, postexercise cooling might be regarded an adverse treatment from a training perspective (37). Yamane et al. (41) hypothesized that strength training–induced microdamage and cellular and humoral processes within the skeletal musculature are a precondition for repair processes, regeneration of muscle fibers, activation of satellite cells, and the like. A reduction in muscle temperature as a result of CWI might disrupt or suppress these adaptive processes, leading to a delay instead of an improvement in muscular performance in hypertrophy training (11,37,41). Barnett (3) pointed out that inflammatory processes play a central role during recovery for the repair of damaged muscle structure and for adaptation, and therefore, measures that suppress these processes are contraindicated. Another explanation for the lower training adaption of the cooled leg might be seen in the fact that CWI can negatively affect capillary permeability, the release of circulating hormones (such insulin-like growth factor-1, testosterone, and growth hormone), and blood flow (12,21,31,39). A further potential mechanism for muscle hypertrophy may be an increase in intracellular water content. This so-called cell swelling stimulates anabolic processes both by increasing protein syntheses and decreasing protein breakdown (12,16). In addition, it may trigger proliferation of satellite cells and facilitate their fusion to hypertrophying myofibres. Cold-water immersion may negatively influence these processes as well (21,32).
In addition to the above-mentioned rationales, Al Haddad et al. (1) observed that a daily, 5-minute CWI resulted in improved resting parasympathetic activity and improved quality of sleep and also subjective well-being in high-level swimmers. These likely beneficial recovery effects were evident for 24–72 hours. Furthermore, blood lactate concentrations were lower after CWI. The authors hypothesized that this might be because of an increased blood circulation in the relevant musculature, which positively affects lactate depletion. Currently, it is discussed to what extent lactate itself functions as a training stimulus at the cell level (33).
From the present results, we cannot conclude to what extent the applied hydrostatic pressure on the cooled leg side was responsible for the lower strength gains. In principle, because of the hydrostatic pressure, the immersion of the body or of body segments results in an increased transportation of metabolic products (e.g., lactate) from muscle tissue, reduced peripheral resistance, and reduced neuromuscular activity (10,39).
The observed deteriorations in training effects in the cooled leg were small. A difference of 1–2% over a period of 5 weeks might be regarded negligible. Nevertheless, to date, most studies that analyzed the recovery effects lasted maximally 1 week, and the recovery effects as compared with a passive control condition were also small (up to 1.8–4.3% dependent on the time after CWI when performance was analyzed) (20,29). In addition, there are other recovery modalities, which showed smaller differences to CWI (e.g., contrast water therapy, active recovery, hot shower) (11,22,23). Although these studies analyzed short-term recovery effects over a period of maximally 1 week, recovery during longer periods has been not evaluated yet. The observed recovery effects and the possibly reduced training adaptations might be regarded practically relevant from the viewpoint of high-performance sports. Thus, from a sports practical perspective, the uncritical use of CWI during longer training camps should be carefully handled. It seems advisable that the short-term recovery effects should be balanced against possibly reduced long-term training adaptations.
Obviously, some limitations of the present study need to be addressed. We did not evaluate high-level athletes. Thus, the transferability to professional sports remains questionable. Well-controlled studies to analyze specific and small but possibly relevant effects are complicated in athletes because their training routine affects the framework for scientific studies and confounding factors can hardly be eliminated. The participants in the present study had strength training experience, and a well-controlled training situation was created, and thus, internal validity seems high. A further limitation might be seen in the fact that the training stimulus was a very specific, isolated strength task and not very functional in nature. However, the training stimulus was highly standardized. In addition, we used a moderate-intensity protocol aiming on muscle hypertrophy. Studies that investigated the effects of cold applications on strength recovery usually used high-intensity eccentric protocols (29). The training mode that was applied in the present study, however, is widely used in sports practical settings (13,30), and nowadays, athletes often use CWI as recovery modality after routine strength training. We used a within-subject repeated-measures experiment to minimize interindividual differences and randomized the leg for control or cooling condition. We cannot exclude any cross-talk effect from one leg to the other. Also, cooling may have suppressed the release of growth factors. Such a reduced release of growth factors can be expected to be transferred from the cooled to the control leg via humoral pathways, and thus, training adaptations may have been diminished in the uncooled leg, too. However, this must remain speculative and warrants further research (34).
This pilot work was conducted to assess possibly small but relevant effects of CWI on adaptations in a well-controlled situation with a clear and defined task. As a next step, this approach needs to be transferred to a sports practical setting and to higher level athletes.
From the results of the present study, it is concluded that CWI can have a negative impact on strength training adaptations in sports students with strength training experience. The small deteriorations in training adaptations in the long term should be balanced with the possible beneficial short-term recovery effects of CWI. The transferability of the results to a higher performance level together with the optimal scenarios for the application of CWI as a recovery means in a practical setting need to be addressed in future research. In addition, scientific efforts with regard to the physiological mechanisms that may cause reduced training adaptations as a consequence of cold applications seem warranted (e.g., by means of muscle biopsies).
The authors acknowledge the access to facilities for testing and training by the Olympiastützpunkt Rheinland-Pfalz/Saarland, especially Prof Hanno Felder for further support. In addition, Jan Neubauer is acknowledged for his valuable assistance with the study execution. This study was undertaken with no external financial support, and there are no conflicts of interest to declare.
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