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APPLIED SCIENCES

Postexercise Cold Water Immersion Benefits Are Not Greater than the Placebo Effect

Broatch, James R.1,2; Petersen, Aaron1,2; Bishop, David J.1

Author Information
Medicine & Science in Sports & Exercise: November 2014 - Volume 46 - Issue 11 - p 2139-2147
doi: 10.1249/MSS.0000000000000348
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Abstract

To be successful in their chosen sport, athletes must achieve an adequate balance between training and recovery. Inadequate recovery between training sessions can place great physiological strain on an athlete, potentially leading to symptoms of overreaching, fatigue, and reduced performance (28). Optimizing recovery between training bouts and competition is frequently recommended to ensure that athletes can train frequently while reducing these associated risks. A large body of research has focused on modalities designed to hasten recovery after exercise, with one of the most prevalent techniques being cold water immersion (CWI) (4).

CWI is believed to attenuate postexercise reductions in functional capacity and athletic performance (41). Although the specific underlying mechanisms remain to be elucidated, hydrostatic pressure and a reduction in muscle temperature (Tm) may assist in reducing edema, pain, and the accumulation of metabolites (9,41). The physiological benefits of CWI reported to date include improved recovery of exercise performance (3,17,27,36,37) and reduced muscle soreness (2,29,30). However, many studies have reported CWI to have no influence on the recovery of exercise performance (30,31,33) or in reducing edema and muscle soreness (16,31).

An important unanswered question is whether the variable response to CWI can be attributed, at least in part, to psychological factors (33). Other recovery techniques, such as massage, have been reported to improve recovery via psychophysiological mechanisms that include decreased sensation of pain and fatigue (38). CWI has been shown to enhance feelings of recovery (24) and reduce perceptions of fatigue (24,30,33,34) and muscle soreness (3,17,30,34) when compared with a control condition. Furthermore, a recent meta-analysis by Leeder et al. (20) concluded that CWI is effective in reducing subjective measures of muscle soreness up to 96 h postexercise, with its effects on muscle function unclear. Given the subjective nature of muscle soreness and the increasing popularity of CWI as a recovery strategy, it is plausible that athletes believe and expect CWI to improve recovery from exercise.

One major weakness of CWI research performed to date is that no study has incorporated a placebo condition. This is a crucial omission given that the placebo effect is a well-accepted phenomenon within medicine and is even used as a therapeutic intervention (5). The placebo effect also influences sport performance (5) and has a potentially long-lasting effect (7). Merely expecting an intervention to have a positive effect has been shown to improve an athlete’s performance (22). Pollo et al. (26) reported a 7.8% decrease in perceived fatigue and an 11.8% increase in leg extension strength when supplying an ergogenic placebo. To fully understand the mechanisms underlying CWI and its influence on athletic performance it is therefore crucial to control for the placebo effect.

The aim of this study was to address this limitation and compare for the first time the effects of CWI to those of a placebo condition (thermoneutral water immersion placebo (TWP)) that participants were informed was as effective as CWI. It was hypothesized that the placebo effect would be, at least in part, responsible for any observed benefits of CWI—i.e., TWP and CWI would elicit similar benefits in recovery but superior benefits when compared with those of a thermoneutral water immersion control condition (TWI). In addition, to assess any potential influence of reduced Tm, independent of the effects of hydrostatic pressure on recovery, CWI was compared with TWI.

METHODS

Participants

Thirty recreationally active, healthy males (mean ± SD: age, 24 ± 5 yr; body mass, 78.7 ± 8.5 kg; height, 179.3 ± 6.6 cm; V˙O2peak, 51.1 ± 7.0 mL·kg−1·min−1) participated in this study. Informed consent was obtained before participation, and all participants were screened for immunological irregularities and cardiovascular risk factors associated with exercise. All procedures were approved by the institution’s human research ethics committee.

Overview

Each subject participated in five laboratory sessions over a 2-wk period (Fig. 1). The study followed a parallel group design, in which participants were assigned to one of three recovery conditions in a randomized, counterbalanced fashion. These conditions were CWI (n = 10), TWP (n = 10), or TWI (n = 10).

FIGURE 1
FIGURE 1:
Schematic representation of the experimental design.

The initial testing session was a familiarization session. Anthropometric measurements (height, mass, and quadriceps skinfold thickness of the dominant leg) were taken, followed by familiarization with the maximal voluntary isometric contraction (MVC), pain threshold/tolerance (algometer), thermistor insertion, acute high-intensity interval training (HIT), and recovery protocols. Two days after the familiarization session, participants attended the laboratory (session 2) to complete a graded exercise test (GXT) to determine peak oxygen uptake (V˙O2peak).

After the preliminary sessions, participants completed session 3, which comprised the acute HIT session and designated recovery condition. Intramuscular temperature was documented during the exercise and recovery protocols of this session. An antecubital venous blood sample, girth and pain threshold/tolerance measures of the quadriceps of both limbs, and completion of a psychological questionnaire were performed before (baseline) and immediately after the HIT session (postexercise (PE)), immediately postrecovery (PR), and 1, 24 (session 4), and 48 h (session 5) after the HIT session. An MVC of the dominant leg knee extensors was also performed at these time points, with the exception of PE (participants were unable to give maximal effort while the thermistor was still inserted). Belief in the recovery effectiveness was assessed at the start (BEpre) and end (BEpost) of the study via a “belief questionnaire”. Participants were asked to fast for 2 h and refrain from exercise for the 24 h preceding sessions 3, 4, and 5. Food diaries were recorded for the 24 h preceding session 3, and participants were asked to replicate this diet for the 24 h preceding sessions 4 and 5. Participants were allowed to consume water ad libitum during all sessions.

GXT

The GXT was performed on an electronically braked cycle ergometer (Excalibur Sport v2.0; Lode, the Netherlands). After a 3-min warm-up at 75 W, the test increased by 30 W each minute thereafter until the participant reached volitional fatigue. Expired gases were analyzed every 15 s using a metabolic cart (Moxus Metabolic System; AEI Technologies, Pittsburgh, PA), which was calibrated using known gas concentrations before each test (20.93% O2, 0.04% CO2 and 16.10% O2, 4.17% CO2; BOC Gases, Australia). Participants were instructed to maintain a pedaling cadence of 70 rpm and to wear an HR monitor (RS800sd; Polar Electro Oy, Finland) during the test. The test was stopped when pedaling cadence dropped below 60 rpm. The V˙O2peak was defined as the average of the two highest consecutive values reached during the test.

Intramuscular thermistors

The site for thermistor insertion was determined as 5 cm lateral to the midpoint between the participant’s anterior superior iliac spine and the head of the patella on the dominant leg. An 18-gauge needle (Optiva IV Catheter 18G × 1.75″; Smiths Medical) was inserted at the marked site, after which, it was subsequently removed while leaving the catheter in the quadriceps muscle. A needle thermistor probe (Model T-204A; Physitemp Instruments, Clifton, NJ) was inserted through the catheter to a depth of 4 cm plus half the width of the thigh skinfold. The thermistor probe and catheter were securely covered and fastened to the leg, allowing for movement and continual measurement (4 Hz) of Tm. Complete temperature data sets were available for 23 participants (CWI, n = 9; TWP, n = 6; TWI, n = 8) as a result of the thermistors occasionally malfunctioning during high-intensity exercise.

HIT session

The exercise protocol used in this study represents an increasingly popular form of high-intensity training (14). On an electronically braked cycle ergometer (Excalibur Sport v2.0; Lode, the Netherlands), participants first completed a 5-min warm-up at 100 W. This was immediately followed by 4 × 30-s “all-out” efforts at a constant resistance corresponding to 7.5% of body mass, separated by 4 min of rest. To eliminate individual variance with self-administered “speeding up” of the flywheel, participants began each effort from a rolling start corresponding to 20 rpm lower than the peak cadence (rpm) reached during familiarization. The tester manually sped the flywheel to the desired cadence (rpm) before strapping the subject’s feet to the pedals 15 s before each effort. During the effort, participants were given extensive verbal encouragement and asked to remain seated in the saddle.

Recovery interventions

Five minutes after completing the HIT session, participants performed their assigned recovery intervention for 15 min. Seated (with legs fully extended) in an inflatable bath (iBody; iCoolsport, Australia), participants were immersed in water up to their umbilicus. Water temperature was maintained with a cooling/heating unit (Dual Temp Unit; iCoolsport, Australia), with validations taken every 3 min with a thermometer immediately adjacent to the thermistor site. TWI and TWP temperatures were maintained at 34.7°C ± 0.1°C, and CWI temperatures were maintained at 10.3°C ± 0.2°C. The CWI protocol was based on a pilot work comparing the Tm drop elicited from an HIT bout and subsequent 15 min recovery in 14°C (2.7°C ± 1.7°C) or 10°C (4.7°C ± 3.1°C) water. To facilitate the placebo effect, a deidentified, pH-balanced, dissolvable skin cleanser (Cetaphil Gentle Skin Cleanser; Cetaphil, Australia) was added to the water for the TWP condition in plain sight of the participant immediately before immersion. Investigators were not blinded to the experimental condition, as this was revealed with different limb temperatures when taking girth and algometer measures. Given its popularity in recovery (4), it was assumed that most participants had previous knowledge of CWI’s purported benefits. To eliminate any potential bias, participants in the placebo condition were led to believe that a thermoneutral water immersion (with the addition of the skin cleanser) was beneficial in recovery from high-intensity exercise, which we considered to be more effective than convincing participants that CWI was detrimental.

Thermal sensation and comfort

During water immersion, thermal comfort (Tc) and sensation (Ts) were measured every 3 min using subjective visual scales (13). The scales ranged from “very comfortable” to “very uncomfortable” (white to black scale) for Tc and from “very cold” to “very hot” (green to red scale) for Ts. Corresponding scores ranging from 0 to 20 were on the reverse side of each scale and only visible to the tester.

Recovery information sheets and belief questionnaires

At the beginning of the familiarization session, participants were given an information sheet on the efficacy of their assigned recovery modality. CWI participants were shown peer-reviewed data on its effectiveness for repeat cycling performance (37). TWP participants were falsely led to believe that they were using a newly developed “recovery oil”, which was as effective as CWI in promoting recovery from high-intensity exercise. TWI participants were shown information on the benefits of water immersion alone without an associated cold or “recovery oil” influence (41). Apart from the addition of the skin cleanser, the TWP and TWI conditions were identical. After familiarization with the MVC and algometer measures and before familiarization with the HIT and recovery protocols, subjects were asked to complete a “belief” questionnaire designed to measure the anticipated effectiveness of their assigned recovery technique (BEpre). Participants were instructed to mark an “X” on a five-point Likert scale between two extremes (0 indicating “not effective at all” and 5 indicating “extremely effective”). Approximately 5 min after the 48-h MVC (session 5), participants were asked to complete a similar “belief” questionnaire designed to measure the perceived effectiveness of the completed recovery condition (BEpost).

Psychological questionnaire

Participants were required to complete a psychological questionnaire documenting subjective ratings of readiness for exercise, fatigue, vigor, sleepiness, and muscular pain. Instructions were given to mark an “X” on a 10-cm visual analog scale between two extremes (0 = “least possible”, 10 = “most possible” for each rating), as described previously (31).

MVC

Muscle strength and power of the dominant leg knee extensors were measured using an isokinetic dynamometer (Cybex Isokinetic Dynamometer; Humac NORM, Canada). Participants were positioned to ensure that the axis of rotation aligned with the femoral condyle. After an initial warm-up of three submaximal efforts (50%, 70%, and 90% MVC), participants completed three maximal 5-s isometric contractions of the knee extensors, with 30 s of rest between each repetition. The knee extension angle was set at 60°, as previously described (39,40). The greatest peak (MVCpeak) and mean (MVCavg) torque achieved from all repetitions were recorded. This effort was also used to determine the rate of torque development (RTD). Absolute RTD was calculated from the average slope of the torque–time curve (Δtorque/Δtime) from contraction onset (torque >; 7.5 N·m of baseline) to 200 ms (1).

Blood analyses

A 20-gauge indwelling venous catheter (Optiva IV Catheter 20G × 1.75″; Smiths Medical) was inserted into an antecubital vein 10 min before the first blood draw. Blood samples (approximately 10 mL each) were collected into EDTA tubes (Greiner Bio-One, Germany) and analyzed immediately for total leukocytes, neutrophils, and lymphocytes (KX-21N; Sysmex, Japan). The remaining whole blood was centrifuged at 1000g and 4°C for 10 min. The acquired plasma was stored at −80°C for subsequent analysis. All samples were analyzed for interleukin 6 (IL-6) by enzyme-linked immunosorbent assay with commercially available multiplex kits (Fluorokine Multianalyte Profiling Kit; R&D Systems). All samples were analyzed in duplicate. The IL-6 assay had an inter-/intraassay coefficient of variation of <9.4% across the range of 0.2–10.2 pg·mL−1.

Thigh girth

Girth measurements were taken at the midpoint of the thigh on both limbs as an objective measure of exercise-induced edema. With the participant standing, the thigh midpoint was determined as 4 cm distal to halfway between the greater trochanter and lateral epicondyle (19). Thigh circumference was measured around the thigh and over this mark while the subject lay supine on a table, with the foot on the table surface and the knee at 90°.

Algometer

Objective measures of the pain threshold (PTH) and pain tolerance (PTO) were taken using a pressure algometer (FPX Algometer; Wagner Instruments) applied to midbelly sites on the quadriceps of both limbs. The assessment site was located at the point at which the girth circumference site met the line between the anterior superior iliac spine and the head of the patella. With the participant instructed to relax the muscle, pressure was applied perpendicular to the long axis of the femur at a rate of 1 kg·cm−2·s−1 (12). The same instructor was used for all measurements. The first point at which discomfort and unbearable pain was reported corresponded to PTH and PTO, respectively. The algometer had a 1-cm2 application surface, and readings were displayed in kilograms of force.

Statistical analyses

Data are reported in the text as mean ± SD, unless otherwise stated. For parametric data, comparisons between conditions were analyzed using a multifactorial mixed linear model (SPANOVA) with repeated measures for time. The Fisher LSD post hoc test was performed when statistical significance was present. Data that violated the Levene test of homogeneity was log-transformed before analysis. The Friedman two-way ANOVA was used for nonparametric data not belonging to a particular distribution (psychological questionnaires). The Pearson correlation coefficient (r) was calculated (pooled data) to examine the relation between recovery belief (BEpre) and exercise performance (recovery of MVCpeak and MVCpeak from baseline to 48 h). The level of significance for all data was set at P < 0.05. The mentioned analyses were performed using IBM SPSS Statistics v20 (IBM Corp.). In addition, effect sizes (ES) were calculated for results that approached significance (0.05 < P < 0.10). The pooled SD was calculated when the SD values were unequal. Cohen conventions for ES were used for interpretation, where ES equal to 0.2, 0.5, and 0.8 are considered as small, medium, and large, respectively.

RESULTS

Acute HIT session

All groups performed similar volumes of total work during the acute HIT session (302.6 ± 14.8 kJ (CWI), 291.4 ± 42.2 kJ (TWP), and 324.0 ± 54.7 kJ (TWI) (P >; 0.05)).

Tm

For all conditions, Tm increased significantly from 36.0°C ± 0.7°C to 37.6°C ± 0.7°C as a result of exercise (P < 0.05). After 15 min of immersion, CWI induced a 9.5% ± 10.3% reduction in Tm, significantly larger (P < 0.05) than those in both the TWP (0.4% ± 0.8%) and TWI (0.5% ± 0.3%) (Fig. 2).

FIGURE 2
FIGURE 2:
T m (4 cm into the vastus lateralis muscle) during the HIT and 15-min recovery protocols. Values are mean ± SEM. E1–4, HIT effort 1, 2, 3, and 4; W-UP, warm-up. *Significantly different from both TWP and TWI (P < 0.05).

Psychological measures

Tc and Ts were the same for TWI and TWP during immersion. Participants perceived themselves to be significantly colder (Ts, P < 0.05) and more uncomfortable (Tc, P < 0.05) in CWI as opposed to both TWI and TWP. BEpre was significantly greater (P < 0.05) for the TWP and CWI groups when compared with that in the TWI group (Table 1). There was no difference between the CWI and TWP conditions for BEpre or between any groups for BEpost.

TABLE 1
TABLE 1:
Subjective ratings of perceived recovery effectiveness (belief effect) before (session 1, BEpre) and after (session 5, BEpost).

Readiness for exercise and vigor were significantly lower at PE (P < 0.05) compared with those in baseline for all conditions (Table 2). In addition, PE participants felt significantly more fatigued and in more muscular pain than at baseline for all conditions (P < 0.05). Mental readiness for exercise was higher for TWP participants compared with that in TWI at PR (P < 0.05) and 48 h (ES = 0.96, P = 0.052). In addition, compared with TWI participants, TWP participants were more vigorous at PE (ES = 0.93, P = 0.063) and in less pain at PR (P < 0.05). In comparison with CWI participants, TWP participants reported a lower physical readiness for exercise at 24 h (ES = 0.74, P = 0.075) and a lower rating of vigor at PR (P < 0.05). When compared with TWI participants, CWI participants felt more physically ready for exercise at PR and at 1 and 24 h (P < 0.05), more mentally ready for exercise at PR and 1 h (P < 0.05), and more vigorous at PE, PR, and 1 h (P < 0.05).

TABLE 2
TABLE 2:
Subjective ratings of readiness for exercise, fatigue, vigor, sleepiness, and pain.

MVC

There were no differences in MVCpeak (CWI, 250.6 ± 48.7 N·m; TWP, 234.4 ± 63.7 N·m; and TWI, 240.4 ± 85.2 N·m) and MVCavg (CWI, 219.6 ± 43.3 N·m; TWP, 207.0 ± 56.9 N·m; and TWI, 211.6 ± 71.9 N·m−1) at baseline for all groups. MVC performance declined as a result of the HIT session (Fig. 3). At 1, 24, and 48 h, MVCpeak values were 13.1% ± 11.2% (P < 0.05), 11.0% ± 9.0% (P < 0.05), and 8.0% ± 7.0% (P < 0.05) lower than those at baseline for TWI, respectively. Belief effect (BEpre) was significantly correlated to the recovery of MVCpeak (r = 0.52, P < 0.05) and MVCavg (r = 0.41, P < 0.05) over the 48-h postexercise period.

FIGURE 3
FIGURE 3:
Percent changes (from baseline) in MVCpeak (A), MVCavg (B), and RTD (C), for the CWI, TWP, and TWI conditions. Time points are before exercise (baseline), PR, and 1, 24, and 48 h postexercise. Values are mean ± SEM. *Significantly different from that in TWP (P < 0.05). ‡A small effect compared with that in CWI (0.5 >; ES >; 0.2). #A small effect compared with that in TWP (0.5 >; ES >; 0.2).

MVCpeak values were 9.0% (PR, P < 0.05), 10.6% (1 h, P < 0.05), and 12.6% (48 h, P < 0.05) lower for TWI compared with those for TWP. MVCpeak for CWI participants was not significantly different from those in either TWP or TWI conditions at any time point. MVCavg values were 11.0% (PR, P < 0.05), 10.2% (1 h, P < 0.05), 12.3% (24 h, ES = 0.28 and P = 0.06), and 13.2% (48 h, P < 0.05) lower for TWI compared with those for TWP. There were no differences in MVCavg between CWI and TWP at any time point. MVCavg values were 6.8% (PR, ES = 0.48 and P = 0.07) and 9.7% (48 h, ES = 0.43 and P = 0.08) lower for TWI compared with those for CWI.

RTD was lowest for TWI at every time point (Fig. 3). Immediately PR, RTD was 8.1% lower for TWI compared with that for TWP (ES = 0.34, P = 0.06). There were no differences between CWI and TWP for RTD at any time point. At 48 h, RTD was 10.3% lower for TWI compared with that for CWI (ES = 0.48, P = 0.08).

Blood plasma variables

IL-6 concentration was significantly elevated from baseline at PE, PR, and 1 h (P < 0.05) for all conditions. Total leukocyte count was elevated at PE for all conditions (P < 0.05) and returned to baseline at PR. Lymphocyte count was higher at PE than that at baseline (P < 0.05), whereas neutrophil count was significantly lower than that at baseline (P < 0.05) for all conditions. Of the time points measured, neutrophil count was highest at 1 h (P < 0.05) for all conditions. There were no differences between groups for all blood markers (Fig. 4).

FIGURE 4
FIGURE 4:
Blood markers at baseline, PE, PR, and 1, 24, and 48 h postexercise. IL-6 (A), total white blood cell count (B), lymphocyte percentage in white blood cell count (C), and neutrophil percentage in white blood cell count (D). Values are mean ± SEM. WBC, white blood cell. *Significantly different from that in baseline for all conditions (P < 0.05).

Thigh girth and algometer

Thigh girths of both the dominant and nondominant limbs were significantly elevated (P < 0.05) at PE for all conditions and returned to baseline at PR. PTO and PTH did not differ from those at baseline for all conditions. There was also no interaction between groups for all thigh girth and algometer measures.

DISCUSSION

The main finding of this study was that a TWP condition is superior to a TWI condition in assisting the recovery of the quadriceps’ muscle strength after an acute HIT session. This coincided with improved subjective ratings of readiness for exercise and reduced subjective pain ratings in participants assigned to the TWP. CWI participants also displayed superior muscle strength and psychological measures when compared with TWI participants but performed similarly to TWP participants despite a significant reduction in Tm compared with that in the thermoneutral conditions. Furthermore, marked changes in immune markers were evident after an acute HIT session, with no apparent difference between groups.

The results of this study demonstrate for the first time that an acute HIT session, consisting of four 30-s “all-out” cycling efforts, decreased peak quadriceps’ strength by approximately 13% (1 h), approximately 11% (24 h), and approximately 8% (48 h) over a 48-h postexercise period for TWI. Despite the lack of eccentric load and subsequent muscle damage, a protocol of this nature can significantly hinder muscle strength up to 48 h postexercise. Although many mechanisms may be responsible, a reduction in leg strength after high-intensity cycling may primarily be related to the inactivation of muscle cation pumps (21). In particular, sarcoplasmic reticulum Ca2+-ATPase function has been shown to remain depressed for up to 36–48 h postexercise (35). A prolonged reduction in muscle strength after an acute bout of HIT has the potential to hinder an athlete’s capacity to repeat efforts requiring high speed, power, and strength development in subsequent training sessions and/or competitions.

A crucial component of this study was the effective deception of participants administered to the placebo. After reading the information sheets, participants in the TWP condition rated the expected benefits of their assigned recovery protocol greater than the ratings of participants in TWI. This was evident despite the two conditions being identical apart from the addition of bath soap. The effectiveness of the deception is also supported by the psychological questionnaires, by which TWP participants reported greater mental readiness for exercise and lower pain levels immediately PR compared with those of TWI participants. Similar results were observed for the CWI condition. Ratings of physical readiness for exercise, mental readiness for exercise, and vigor were also superior to those in TWI for up to 1 h postexercise. Previous belief in the benefits of CWI, the provided information sheets, and the effects of the cold stimulus itself may all explain these differing perceptions of fatigue and recovery. Given the discomfort reported during CWI, as compared with both thermoneutral conditions, participants may simply expect it to be beneficial. However, apart from CWI participants feeling more vigorous at PR as compared with TWP participants, subjective ratings of fatigue and recovery were superior for both these conditions as compared with those in TWI. As such, participants in the TWP were effectively deceived and led to believe that a placebo was as effective as CWI in promoting recovery from high-intensity exercise and is superior to TWI.

As hypothesized, recovery of quadriceps muscle strength and RTD over the 48-h postexercise period was superior in TWP as compared with that in TWI. Coinciding with the improved psychological ratings, MVCpeak and MVCavg were significantly higher for TWP compared with those for TWI at PR and 1 and 48 h postexercise. Furthermore, there was a trend for an improved RTD (PR) and mean force (24 h) for TWP compared with that for TWI. Given that the only difference between the TWI and TWP conditions was the addition of bath soap, with water depth and Tm similar between the two conditions, this demonstrated that a placebo effect was achieved. In further support of this, BEpre was also significantly correlated to a greater recovery of MVC, demonstrating that belief in the effectiveness of PE recovery may be associated with subsequent performance. By deceiving subjects into thinking that they are receiving a beneficial treatment, participants felt more recovered and a superior performance was witnessed.

Despite a large body of research on the placebo effect in medicine, there are few studies reporting the magnitude and extent of its effect in sports performance (5). Only recently has empirical evidence emerged in support of the placebo affecting athletic performance, encompassing both endurance- (6,11) and resistance-related (18,26) exercise performance. After being informed that an ergogenic aid was likely to improve cycling time trial performance, the placebo effect has been shown to account for a 3.8% improvement in mean power over a 40-km cycling time trial (11) and a 2.2% increase in mean power over a 10-km cycling time trial (6) when given a carbohydrate and caffeine placebo, respectively. Alternately, both caffeine and amino acid placebos were reported to improve leg extension strength (total work performed during repeated repetitions until fatigue at 60% one-repetition maximum) by 11.8% after 72 h (26) and one-repetition maximum leg press by 21.1% after 48 h (18), respectively. The current study, in comparison, has demonstrated improved maximal (12.6%) and mean torque (13.2%) during an MVC of the quadriceps, 48 h after exercise, when administered to TWP as compared with those in TWI. As such, this study has demonstrated that influencing one’s belief in the efficacy of thermoneutral water immersion as an ergogenic aid in recovery can account for approximately 13% improvement in muscle strength 48 h after high-intensity exercise.

This is the first study to test the hypothesis that the acute benefits of CWI may at least be partly placebo related and that altered perceptions of fatigue play an important role in recovery from exercise. Consistent with past literature (3,27,32,36), the CWI condition demonstrated a favorable return of muscle strength up to 48 h postexercise, as compared with that in the TWI condition. Despite recent suggestions that the efficacy of CWI in recovery is limited to only subjective measures of pain and soreness (10,20), this study has demonstrated that it is also beneficial for the recovery of the quadriceps leg strength after HIT. However, the recovery of isometric leg strength and RTD during the 48-h postexercise period followed the same pattern in the CWI and TWP conditions, with no significant differences between groups and both conditions demonstrating a favorable return to baseline when compared with that in TWI. As such, when compared with TWP, a significantly colder water immersion and greater reduction in Tm (approximately 3°C) in the CWI condition were not associated with greater recovery of muscle strength and RTD during an MVC. This is the first reported evidence that the manipulation of one’s expectation of recovery via a CWI placebo (i.e., TWP) can have a similar beneficial influence on the recovery of muscle strength as that of CWI itself. Previous research has alluded to the fact that the placebo effect may contribute to observed performance and physiological benefits after half time cooling between two cycling efforts (15) and CWI after eccentric loading of the quadriceps (31). The findings of the current study have confirmed that the placebo effect may account for some of the observed benefits after CWI or, alternatively, that it is as strong as these physiological benefits.

The simultaneous assessment of objective physiological and performance variables with the subjective psychological and perceptual measures strengthens the suggestion of a placebo effect. Similar to previous research, an acute bout of high-intensity anaerobic exercise promoted an increase in thigh girth (36), circulating leukocytes (33), and IL-6 concentration (23,33) for all conditions. However, an approximately 3°C reduction in Tm did not influence these measures, suggesting that CWI has no influence on these physiological markers. The acute immune response and elevation in the myokine IL-6 reported in the current study are consistent with those reported previously (23) but could be a result of elevated body temperature and/or metabolic status after high-intensity exercise (25). Whether this response is associated with a prolonged reduction in leg strength, and whether CWI could attenuate such a response, is unclear. Future research is warranted to investigate this issue, including comparisons to an exercise protocol likely to cause significant muscle damage, edema, and inflammation. Alternately, CWI (or the protocol used in this study) may not have induced the physiological response necessary to enhance recovery and improve performance. The apparent differences in MVC performance between groups, despite no difference in the physiological markers measured, reinforce the possibility of a CWI placebo effect. Altered perceptions of readiness for exercise and fatigue have the potential to influence performance but will have little influence on physiological processes. These findings again highlight a potentially greater psychological role of CWI in recovery than the commonly hypothesized physiological role.

Practical applications/implications

Similar improvements in performance after CWI or a CWI placebo have highlighted the importance of belief in recovery. Regardless of any potential physiological role, it is important for coaches and sport scientists alike to educate their athletes on the benefits of recovery and also encourage belief in the practice. This is particularly pertinent for athletes more responsive to the placebo effect because it is well documented that some individuals show remarkable responses to placebo interventions whereas others may not respond at all (8). A strong belief in CWI, combined with any potential physiological benefits, will maximize its worth in recovery from exercise. Future research in this area should investigate whether alternate exercise protocols (e.g., resistance training) would elicit a similar placebo effect. It is possible that CWI is more appropriate as a recovery modality after exercise or sport inducing a large degree of muscle damage or contusion injury. Furthermore, future research should investigate whether these results can be replicated in well-trained athletes and whether this placebo effect can influence athletic performance.

CONCLUSIONS

A HIT protocol of four 30-s maximal sprints can elicit a significant increase in Tm accompanied by a significant reduction in muscle strength up to 48 h postexercise. Despite being the same condition and eliciting the same physiological response, a CWI placebo administered after HIT was superior in the recovery of muscle strength as compared with a TWI control. A CWI placebo is also as effective as CWI itself in the recovery of muscle strength over 48 h. This can likely be attributed to improved subjective ratings of pain and readiness for exercise, suggesting that the hypothesized physiological benefits surrounding CWI may be at least partly placebo related.

Acknowledgment is given to Prof. Remco Polman, Dr. Lauren Banting, and Dr. Xu Yan (Institute of Sport, Exercise, and Active Living) for their assistance in the study design and data analysis and to the participants for their generous involvement in this study.

The authors also acknowledge the generous funding of Exercise and Sports Science Australia and their Applied Sports Science research grant (received in 2011).

The authors declare no conflicts of interest.

The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

HYDROTHERAPY; RECOVERY; INFLAMMATION; HIGH-INTENSITY INTERVAL TRAINING; MUSCLE TEMPERATURE

© 2014 American College of Sports Medicine