The use of hydrotherapy as a recovery modality is now a common practice during the initial postexercise period for athletes. The increased demand for optimal postexercise recovery has led to a wealth of research investigating the influence of such a practice on the acute-phase response (5,17,18), markers of muscle damage (5,17,18), perceptual ratings of well-being (5,14–18,20), and subsequent athletic performance (5,14–18,20). Throughout this research, strategies such as cold water immersion (CWI) or contrast water therapy (CWT–which encompasses periods of alternate hot and cold water exposures) have been used to optimize an athlete's recovery from exhaustive and muscle damaging exercise, with mechanisms such as analgesia, hydrostatic pressure, and the action of a muscle pump reported as possible rationale for benefit (22). Recently, it has been shown that CWI for a period of approximately 15 minutes after exercise can result in the maintenance of work output during subsequent endurance-based activity (15). Additionally, CWI has been shown to improve the ability to perform tasks of strength and power in the 48–72 hours after the exercise period (after both resistance and team sport exercise), when compared with passive and active recovery protocols (5,17,18). Alternatively, CWT protocols incorporating alternate hot and cold water exposures of 1–2 minutes each, for an elapsed time of approximately 15 minutes have been shown to reduce edema and are also associated with smaller reductions and faster restorations of strength and power activities during the 72 hours after the exercise period (17,18). Furthermore, both CWT and CWI have been shown to reduce the perceptions of muscle soreness over the 24-hour postexercise period (5), and as such, it is suggested that these 2 hydrotherapy methods can help reduce both the physiological and functional deficits that are associated with the delayed onset of muscle soreness (17).
With the use and benefits of hydrotherapy well researched, the attention of sports science practitioners is forever evolving and seeking new methods of recovery that may enhance athletic performance. With this in mind, a relatively underresearched recovery modality for athletes is the use of supplemental oxygen. To date, the majority of research in this area has been conducted in unhealthy populations, such as those suffering with chronic obstructive pulmonary disease (COPD). In these populations, the use of supplemental oxygen provided during the recovery period after exercise has been shown to speed the recovery time from dynamic hyperinflation; however, little influence was seen on the perception of breathlessness or dyspnea (8,14). When trialed in healthy athletic populations, the use of supplemental oxygen provided during the recovery periods between interval repetitions was shown to speed up the rate of hemoglobin resaturation (12). However, no effect has been shown on the athletes' postexercise blood lactate clearance rates, their perceptual ratings of recovery between exercise repetitions, or on their athletic performance during subsequent bouts of exercise that are conducted within a short duration of time after the previous bout (12,23). Additionally, to date, no known research has considered the use of supplemental oxygen in the postexercise recovery period to influence the acute-phase response; nor is it known how such a recovery protocol may affect the postexercise perception of recovery, or how athletic performance in a subsequent training session might be impacted.
To this end, it was the aim of this investigation to explore the recovery effects of hyperoxic gas inhalation on the postexercise cytokine response, the levels of perceptual recovery, and on the next day athletic performance, when compared with a the more commonly used CWT and a control trial of passive rest. It was hypothesized that the CWT and supplemental oxygen trials would result in an enhanced next day athletic performance as a result of a reduced inflammatory response and because of a greater perception of recovery.
Experimental Approach to the Problem
This investigation compared the effects of supplemental oxygen, CWT, and passive rest as recovery modalities on postexercise cytokine responses, perceptual recovery, and subsequent day performance in well-trained swimmers. The study design incorporated 3 experimental trials, which were implemented in a counterbalanced repeated-measures fashion.
Eight highly trained (5 men and 3 women), middle- and long-distance athletes were recruited from the Western Australian Institute of Sport (WAIS) Swimming Program for participation in this investigation (age, 24 ± 4 years; height, 175.7 ± 7.1 cm; mass, 68.1 ± 7.5 kg; Σ7skinfolds, 61.9 ± 31.8 mm). The group consisted of 4 international level swimmers (including 1 dual Olympian and 1 Commonwealth games medallist) and 4 national level swimmers (all having competed at the Australian National Championships). At the time of this investigation, all participants were in the general preparation phase of their training cycle.
Participants were informed of the requirements and risks associated with their involvement in this study, before written consent acknowledging these details was obtained. Institutional Review Board (IRB) approval for the use of human subjects during this investigation was granted by The University of Western Australia's Human Research Ethics Committee (IRB RA/4/1/4385).
During the experimental period, participants were required to attend 3 swimming-based testing sessions, each completed in a 50-m indoor swimming pool (heated to 26 ± 0.5°C) at the Challenge Stadium Swimming Complex (Mt Claremont, Western Australia, Australia). Each experimental trial was separated by exactly 7 days and commenced at 16:00 hours to avoid any diurnal influences of circadian rhythm.
Upon arrival to the pool, participants were required to provide a pre-exercise venous blood sample from the forearm, before a standardized swimming warm-up was commenced. At the conclusion of the warm-up, a brief transition period was allowed, before the athletes completed a main swim-set of 20 × 200 m efforts. During this main set, the swim time, heart rate (HR), and a rating of perceived exertion (RPE) were collected at the immediate completion of every fourth 200-m repetition. Additionally, a blood lactate (BLa) sample was collected at the immediate completion of the final 200-m repetition. A standardized swim-down followed the completion of the 20 × 200 m main set. Throughout the duration of the swim session, each athlete was allowed to consume water ad libitum, up to a maximum of 1 standard-sized drink bottle (600 mL). Additionally, upon exiting the pool, all participants were required to consume 300 mL of a 6% carbohydrate drink (Gatorade, Australia Pty Ltd, Victoria, Australia) before providing a postexercise venous blood sample from the forearm.
Subsequent to this second venous blood collection, the participants then completed one of three 30-minute recovery modalities, which were applied in a counterbalanced repeated-measures order. The three 30-minute recovery modalities included the following:
- CWT: The CWT required participants to alternate 1-minute water immersions between a cold water bath (12°C) and a hot water spa (38°C) for a period of 10 minutes. Subsequently, a 10-minute period of static stretching was completed, before a second 10-minute period of CWT was commenced. This protocol was established as a result of previous research that has shown benefits to perceptual responses and athletic performance from 10 to 15 minutes of accumulated CWT (5,17,18), in combination with the common recovery practices that are currently used within the WAIS swimming program.
- Hyperoxic gas inspiration (HYP): The HYP recovery required the seated participants to inhale a hyperoxic gas mixture (99.5% FIO2) for a 10-minute period, provided through a face mask at a flow rate of 10 L·minute−1. Subsequently, a 10-minute period of static stretching was completed before a second 10-minute period of hyperoxic gas exposure was given. Because there is little preexisting research to suggest the best practice for such a postexercise recovery intervention, this protocol was established to replicate the protocol of the CWT, allowing an effective comparison of outcomes between trials.
- Passive rest (CON): The CON recovery required participants to undertake a 30 minutes of passive seated rest, serving as a control condition.
At the conclusion of the 30-minute recovery period, participants rated their perception of recovery quality, before a final venous blood sample was collected from the forearm. Finally, the well-being of the athlete was ascertained before they were allowed to leave the testing facility with instructions not to partake in any further modes of recovery (i.e., stretching, massage, CWT, compression garments, etc) or physical activity until the following day. Additionally, participants were also strongly encouraged to record and replicate their nutritional habits during this subsequent 12-hour period.
Twelve hours later (07:00), the participants returned to the testing facility to complete a 200-m time trial swim, acting as a postrecovery test of the next day performance. Initially, the participants were required to rate their perceptual recovery from the subsequent nights session, before completing a standardized warm-up, similar to that used before the 20 × 200 m main swim set above. The performance test involved a 200-m time trial effort, using a dive start from the competition blocks. After this time trial effort, a standardized cooldown swim was implemented, thus completing the experimental protocol.
20 × 200 m Swimming Session
Before the main swim-set, a standardized warm-up was completed. This warm-up was 1800 m in length and was predominantly freestyle based with various swimming drills and kicking included. The main swim-set comprised 20 × 200 m repetitions. The first 3 of every four 200-m efforts were completed in the freestyle stroke, on a 3 minutes 30 seconds departure cycle. The remaining fourth 200-m effort was completed in the athlete's form stroke on a 2 minutes 30 seconds departure cycle. This block of 4 repeats was completed 5 times through, on a descending effort (1–5), with an estimated HR intensity of each effort decreasing as 40 beats below maximum (bbm), 30 bbm, 20 bbm, 10 bbm, and the final 200 m completed at the maximal intensity. A standardized 1,800-m swim down was completed after each 20 × 200 m test set and was predominantly freestyle based with various swimming drills and kicking included.
Static Stretching Protocol
During the 30-minute recovery period of the HYP and CWT trials, a static stretching routine was enforced for the second 10-minute block of time (i.e., from 10 to 20 minutes of elapsed time). During this period, athletes were provided with a laminated “stretch-sheet,” which illustrated 10 static stretch positions of the body's major muscle groups. The stretches targeted the hamstrings, quadriceps, hip flexors, and gluteals; the lower back and latisimus dorsi; and the external rotators and the posterior shoulder capsule. The static stretching period was enforced by a research assistant, and each stretch was held for a period of 30 seconds on each side of the body. The 10 minutes of static stretching was included as part of the 30-minute recovery period in the HYP and CWT because this practice is common in the recovery procedures currently used within the WAIS swimming program and was thus standardized between the trials.
Blood Sample Collection Preparation and Analysis
Venous blood was collected via venepuncture of an antecubital vein in the forearm with the athlete lying down for a standardized 5-minute period before the collection to control for postural shifts in plasma volume. Venous samples were collected using a 21-gauge needle into an 8.5 mL SST II gel collection tube (BD Vaccutainer; Becton Dickenson, New South Wales, Australia). The blood sample was allowed to clot for 60 minutes at the room temperature, before being centrifuged at 10°C and 3,000 rpm for 10 minutes. The serum supernatant was divided into 1-mL aliquots and stored at −80°C until further analysis was conducted. The frozen serum samples were analyzed at the Fremantle Hospital Pathology Laboratory for circulating levels of the cytokine Interleukin-6 (IL-6). The serum IL-6 was measured using a high-sensitivity commercially available ELISA (Quantikine HS; R&D Systems, Minneapolis, MN, USA) in accordance with the manufacturer's specifications. The assay range was 0.38–10 ng·L−1. The coefficient of variation (CV) for IL-6 determination at 0.49 and 2.78 ng·L−1 was 9.6 and 7.2%, respectively.
All arterialized capillary samples taken for BLa analysis were collected from the earlobe into a handheld blood analyzer (Lactate Pro; ARKRAY Inc., Kyoto, Japan). Before blood collection, the site was cleaned with an alcohol swab, before a small incision was made at the lobe of the participant's ear using a spring-loaded lancet. The initial drop of blood was discarded, and the second blood droplet was collected from the site for analysis.
Heart Rate, Perceived Exertion, and Perceptual Recovery
Heart rate was monitored throughout the experimental trials via a Polar HR monitor (Polar FSX, Kempele, Finland), which was left on the pool deck, and immediately placed on the athletes' chest at the completion of every fourth 200-m repetition. The RPE was rated using the Borg perceptual scale (2), encompassing the anchor points 6 (no exertion at all) to 20 (maximal exertion). Perceived recovery was rated using the total quality recovery (TQRper) scale, encompassing the anchor points 6 (not recovered at all) to 20 (completely recovered). The TQRper was conceptualized by Kenttä and Hassmén (6) and has been widely used in previous research as an indicator of an athlete's perceived recovery (7,11).
The data collected from this investigation is presented as mean and SD. A series of 1-way analysis of variance (ANOVA) were used to determine any between-group differences for the variables measured during the swim set (such as the swim time, HR, RPE, and BLa) to substantiate that the session intensity was matched between trials. A 1-way ANOVA was also used to determine between-trial differences in perceptual recovery and also to assess differences in the 12-hour postrecovery performance trials. In addition, a 3 × 3 repeated measures ANOVA was used to assess time (pre-, post-, and 30-minute postrecovery intervention) and trial differences in the cytokine response, as an indicator of the influence that each recovery session had on the acute-phase inflammation. Subsequent to these analyses, a least significant difference, pairwise comparison was made where applicable, to clarify any significant main effects. The alpha level was set at p ≤ 0.05.
The swim time, HR and RPE collected at the completion of each fourth 200-m repetition during the 20 × 200 m swim set are presented in Table 1. There were no significant trial differences between the 3 experimental conditions for any of these measured variables (p > 0.05). Furthermore, the BLa samples collected at the completion of the 20th 200-m repetition were similar between the trials (p > 0.05). Thus, suggesting that the intensity of the 3 trials appropriately matched for comparison.
The postexercise IL-6 response is represented by Figure 1. There were no significant differences in the absolute or relative changes in IL-6 levels between trials. However, a time effect specifically showed that IL-6 levels were significantly higher at the completion of the 20 × 200 m swim-set (p < 0.05) and that these levels were significantly lower after 30 minutes of recovery (p < 0.05). The 30-minute postrecovery IL-6 levels were still significantly higher than at baseline (p < 0.05).
The athlete's perceptions of recovery are represented in Figure 2. At the immediate completion of the 30-minute recovery period, these perceptions were significantly lower (p < 0.05) in the CON trial when compared with those in the CWT and HYP recovery modalities. There were no differences between the HYP and CWT trials. Twelve hours later (immediately before the 200-m performance trial), the athletes felt more recovered having completed the CWT when compared with both the CON and the HYP trials (p < 0.05).
12-Hour Postrecovery Performance Trial
The 200-m swim times of the 12-hour postrecovery performance trials were not significantly different between the conditions (HYP, 2 minutes 16.5 ± 5.7 seconds; CWT, 2 minutes 15.9 ± 5.1 seconds; CON, 2 minutes 17.2 ± 5.2 seconds; p > 0.05).
The results of the present investigation have shown that the use of contrast water immersion or supplemental oxygen provided immediately after the exercise can enhance an athlete's perception of recovery significantly more than doing no recovery at all. However, despite this enhanced perceptual response, there was no evidence to suggest any influence on reducing the postexercise acute-phase cytokine response, nor were there any benefits to the next day exercise performance.
Exercise-mediated increases in IL-6 are produced by the active muscle and may have both proinflammatory and anti-inflammatory actions (21). It is suggested that increases in IL-6 are a precursor to a number of immunoregulatory responses, such as an increase in the production of IL-1 receptor antagonist and IL-10 by the lymphocytes, macrophages, and monocytes (1), each of which would require upregulation in the event of an inflammatory reaction. Conversely, the pro-inflammatory activity of IL-6 incurs T-cell activation, B-cell differentiation, and the stimulation of acute-phase protein production by the hepatocytes in the liver (4,19). To this end, it is the multifactorial function of IL-6 that makes this cytokine abundant during periods of inflammation, a common marker used to quantify the severity of inflammation.
In the present investigation, IL-6 was shown to be significantly increased at the conclusion of the swim set in all the 3 experimental conditions and may be representative of the large amount of muscle mass required during swimming. Such postexercise increases in this cytokine have been frequently reported in previous literature but are generally associated with running-based activity (11,13). However, when considering water-based exercise, there are few research articles that have examined the postexercise IL-6 response. Previously, Nemet et al (9) showed that there was a significant postexercise cytokine response associated with a typical 1.5-hour water polo training session in adolescent female athletes. These authors showed that the circulating levels of IL-6 were increased by 375% at the conclusion of the 90-minute session. In the current investigation, the average percentage increase in IL-6 was approximately 705% immediately after exercise and approximately 403% after the 30-minute recovery intervention. The larger increases in IL-6 seen here when compared with Nemet et al (9) might be explained by the fact that our athletes were of the national and international competition standard and were training at an intensity equal to and above their lactate threshold for a duration of approximately 2 hours. Peeling et al (13) previously showed that there exits an influence of exercise intensity and duration on the IL-6 response. Therefore, it is likely that the athletes used in the current investigation were working at a higher intensity and for a longer period than the water polo players examined by Nemet et al (9). Despite these differences in the magnitude of change, the combined results of these 2 investigations suggest that a large cytokine response can be expected from a water-based training session and that these increases might be of similar magnitude to that seen from running-type activities.
When comparing the IL-6 levels between the experimental trials, it was evident that the CWT and HYP had little influence on the acute-phase cytokine response, thereby suggesting that there was little effect of these 2 recovery interventions on any subsequent inflammatory activity. Previously, the use of CWT to influence the inflammatory response has been shown to have similar outcomes to those seen here. In fact, Vaile et al (17,18) and Ingram et al (5) have all shown that the acute-phase response of IL-6, creatine kinase (CK), and C-reactive protein at the conclusion of resistance and team sport activities was similar when CWT was compared with a passive resting control. It has previously been suggested that the hydrostatic pressure of water immersion may act with a compressive force to shift fluid from the periphery to the central cavity (17,22), thereby reducing the acute-phase inflammatory response. However, it would appear that such a proposal is not reflected in the currently measured blood markers that are precursors to or are suggestive of an inflammatory response.
Additionally, there appears to be little research to suggest an influence of supplemental oxygen on the postexercise cytokine response. Although supplemental oxygen has been used during an exercise bout (10), and during the recovery periods between exercise bouts (12), it would appear that there is no current research to assess the application of this strategy as a postexercise recovery method in athletes. When considering the literature pertaining to healthy individuals and patients with COPD, it seems that the provision of supplemental oxygen after an exercise session can assist in speeding the recovery time from dynamic hyperinflation (14). However, other investigations have shown that supplemental oxygen provided at rest (28% FIO2) for a 60-minute period may result in an increase in the circulating levels of IL-6, which has been suggested as an indicative of airway inflammation (3). Contrary to such increases in circulating cytokine levels, the IL-6 response in the HYP trial of the present investigation was similar to that reported in the CWT and CON conditions. Such discrepancies might be explained by the duration of oxygen supplementation being some 40 minutes less in the present investigation or that the acute-phase inflammatory reaction generated in response to the prior exercise session was large enough to mask any subsequent reaction from airway inflammation. Regardless, it was evident from these results that supplemental oxygen will likely not assist in reducing the acute-phase cytokine response to high-intensity training in athletes.
Previous research has independently considered the influence of CWT and HYP on perceptual recovery via the use of perceived soreness, breathlessness, and muscle fatigue scales either recorded immediately after recovery intervention or after 24–48 hours of recovery (5,14–18,20). The results of this previous research show conflicting outcomes on the perceptual responses that are reported. However, similar to the outcomes of the current investigation, it has been suggested that CWT may improve the perception of recovery, with muscle soreness and whole-body fatigue scores rated significantly lower at 30 minutes (20) and 24 hours (5,17) after exercise, when compared with a control condition of passive rest. Vaile et al (17) summarized that some of the potential physiological benefits arising from CWT may include such processes as an increase in substrate transport and an increase in waste product removal. With this in mind, it is possible that an improvement to these physiological processes may have led to the enhancement of the athlete's perception of well-being (and therefore recovery) at the conclusion of the CWT intervention and before the subsequent exercise session on the following day.
However, with respect to supplemental oxygen, there appears to be little research to suggest the influence of such a recovery strategy on postexercise recovery. Previous research has shown that patients with COPD do not present with reduced feelings of breathlessness, nor do they show improved recovery scores of dyspnea when supplemental oxygen is provided after exercise (8,14). Additionally, it has also been shown that supplemental oxygen does not enhance the clearance rate of metabolic waste accumulation (23), nor are there any influences on the acute-phase cytokine response (as shown above). To this end, there seems to be little evidence to explain why the athletes in this investigation may have perceived their recovery to be better in the HYP trial, other than a potential placebo effect of knowing that they were receiving oxygen as a recovery intervention after exercise. However, such a placebo effect in itself may be beneficial to athletes should they feel that their actions are producing a positive effect, and there are no detrimental implications to performance.
It was evident from the results of this investigation that the CWT and HYP interventions had no influence on the 200-m freestyle time trial performed 12 hours later. This outcome occurred despite the athlete's perception of recovery being greater at the completion of each intervention. Previously, the influence of HYP on subsequent athletic performance has been shown to be negligible, even when this exercise is completed as soon as 5 minutes later (8,23). Not surprisingly then, there appears to be no research to date investigating the influence of HYP on the next day exercise performance. As such, the combination of the present investigation and that of previous research might suggest that the effects of postexercise recovery strategies such as HYP may be short lasting and may only act on the acute short-term perceptual senses of an athlete, thus having little influence on the next day athletic performance.
When considering the influence of CWT, it would appear that there are conflicting results reported in the literature. Specifically, Vaile et al (17) showed that 24 hours after a 14-minute CWT intervention, participants were able to produce a significantly greater peak power output during a jump squat task, and a greater peak force output during an isometric squat task, when compared with a passive resting control. Furthermore, Vaile et al (16) also showed that 14 minutes of CWT applied after exercise over the course of a 5-day period resulted in significantly greater sprint and time trial performances during the fourth and fifth day. Such an outcome might suggest that the benefits of water immersion may be experienced over a more chronic training period rather than in an acute instance, thus explaining the lack of influence seen on the next day performance during the current investigation. However, on contrary to those findings above (and more in line with the results of this investigation), alternative research has shown no influence of the 15-minute CWT intervention on the 24- or 48-hour postrecovery performances of a repeated sprint bout, isometric leg strength, or peak power output from a jump squat (5,18). The results of the current investigation are similar to that of these latter 2 investigations, and it might be that the duration of these performance test protocols are too short (i.e., 200-m freestyle time trial approximately 2 minutes 16 seconds; 10 × 20 m sprint approximately 48 seconds (5); maximal jump squat approximately 2 seconds (18)) or that the typical error of measurement associated with these tests is too large to realize the potential beneficial effect from such recovery interventions.
In summary, it would appear that the use of contrast water immersion or supplemental oxygen provided immediately after exercise does not attenuate the acute-phase cytokine response, nor is there any evidence to suggest a benefit on the next day exercise performance. However, it was evident that each of these recovery strategies did enhance the athlete's perception of recovery significantly more than using no recovery intervention at all. This increased perception of well-being may potentially be attributed to an increased substrate transport and waste removal in the CWT or a potential placebo effect in the HYP trial. Regardless, it might be considered that any action taken to enhance an athlete's perception of recovery after exercise may be beneficial should there be no negative consequences to performance.
It is recommended to the coach and sports science practitioner working with high level athletes that a structured recovery session lasting from 15 to 30 minutes in duration should be implemented at the conclusion of a training session because the resultant effects are positive to the athlete's perception of their recovery. From this data, it would seem that a water-based recovery session may produce longer lasting effects on the athlete's enhanced perception of recovery and should thus be the preferred medium used.
The authors acknowledge the assistance of Mr. Matt Magee and the athletes of the WAIS swimming program. Furthermore, the authors also acknowledge the grant funding received from The University of Western Australia's Research Development Awards. This research involves no professional relationships with companies or manufacturers who will benefit from the results presented here. Furthermore, the results of the present study do not constitute endorsement by the authors or the National Strength and Conditioning Association.
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