Sports apparel technology is an active area of research as athletes strive for an edge that will improve their sporting performance. Obvious examples of the application of technology to sport apparel are provided by the novel wet suits and swimsuits used in triathlon and swimming with performance-enhancing buoyancy-aiding and water-resistant properties (37), aerodynamic skin suits used in cycling, or compression stockings used to aid recovery in field sports such as soccer and hockey (6). Although technologically advanced clothing that can demonstrably reduce drag and lower the energy cost of movement can lead to substantial performance benefits (16), other sports clothing applications with novel biological modes of action remain comparatively unexplored.
In the current study, Aquatitan-treated garments were applied to the torso, limbs, and feet of participants; Aquatitan treatment involves the incorporation of titanium particles dispersed in water into fabrics or other products. Similar products are currently commercially available throughout the world with only anecdotal reports of analgesic, endothermic, sedative, and fatigue-reducing effects. However, there is some evidence that Aquatitan treatment may influence pain perception and physical performance via modulation of the peripheral (sensory or motor) and/or central nervous systems (pain perception and memory). Korte (19) found that Aquatitan-treated tape had inhibitory effects on the long-term potentiation of synapses of mouse hippocampal pyramidal neurons involved in pain memory, thus providing support for the reported analgesic effect of Aquatitan-treated products. Furthermore, the effects attributed to Aquatitan-treated tape were removed by placement of a lead plate 0.5 cm in diameter between the hippocampal slice and the Aquatitan-treated tape. Aoi et al. (1) studied the effect of normal light-dark cycles and response to stress in mice placed in cages surrounded by Aquatitan-treated material. Aquatitan treatment substantially reduced spontaneous activity and altered autonomic activity toward parasympathetic dominance. The evidence from hippocampal and murine models suggests that encouraging biological responses to Aquatitan treatment are also possible in humans. The evidence for attenuated pain and sedative autonomic action coupled with anecdotal reports of improved concentration and performance led us to develop the present study to investigate the role of Aquatitan-treated garments in sport performance both in the acute setting and in the days after exposure to exhaustive exercise.
To achieve an ecologically valid outcome while retaining robust and reliable research conditions, we combined simulated match play with laboratory measures in free-living well-trained male soccer and field hockey players. We used the Loughborough Intermittent Shuttle Test (shuttle test) as the primary physical loading activity because it provided a well-established and reliable field test that replicated the physiological demands of intermittent sports such as soccer and hockey (24). The frequent changes in speed and direction associated with sports simulated by the shuttle test involve cyclic eccentric and concentric muscular activities (18,31) and are frequently associated with muscle damage and delayed-onset muscle soreness (DOMS) (18). In professional sports such as soccer, fixture schedules require players to produce optimal performances each match, often without sufficient time for full recovery from previous matches, which makes postgame recovery strategies influential in preparing for the next match (2). The physical demands of repeated performance are especially evident during multiday tournaments such as the FIFA World Cup, where players have exhibited a greater risk of injury and a reduced level of performance (8).
With reference to recovery, numerous studies have investigated physical performance and muscle damage after a prolonged high-intensity exercise (2,18). Running performance (7), isometric strength (2,30), and range of motion (23,30) are all well established as measures of performance and recovery in the days after high-intensity bouts of eccentric exercise. Moreover, indirect markers of muscle damage, such as serum creatine kinase concentration (2,18) and perceived soreness (18), are frequently used to assess recovery from intermittent exercise, whereas pressure-pain threshold has also been shown to be a reliable measure of experimentally induced muscle tenderness (26).
There is anecdotal evidence that Aquatitan-treated products influence muscle soreness and tension and performance outcomes during a high-intensity exercise and in the recovery period after it. Consequently, the purpose of the current study was to investigate the potential ergogenic benefit of Aquatitan-treated products. We chose the shuttle test to determine the immediate effects of treatment on performance and to induce muscle damage and soreness, and we measured performance, range of motion, and psychometric measures to establish the nature of the effects during 4 d of recovery from the shuttle test.
Fourteen trained male soccer and hockey players competing in regional- and national-level competition, aged 25.2 ± 8.4 yr (mean ± SD), and with mean body mass of 75.8 ± 8.2 kg, mean stature of 1.78 ± 0.03 m, and mean maximum oxygen uptake of 60.8 ± 8.3 mL·kg−1·min−1, volunteered to participate in the study. Potential participants were interviewed before undertaking the study and were subsequently excluded if they had a history of cardiovascular or respiratory disease, were smokers, or were currently on analgesic medication. All participants were informed in writing about the potential risks of the study and gave written informed consent for their participation in the study, which was approved by Massey University Ethics Committee.
All participants first completed a preliminary treadmill-based assessment of aerobic power (V˙O2max) to determine running speeds for the shuttle test and subsequent treadmill exercise protocols. This test was followed approximately 1 wk later by a familiarization exercise trial, including introduction to the measures for joint range of motion, pressure-pain threshold, perceived muscle soreness, isometric strength, and a 15-min block of the shuttle test protocol. Each experimental block consisted of baseline measurements for perceived soreness, psychological parameters, blood markers of muscle damage, joint range of motion, and isometric strength, followed by the shuttle test. Recovery was assessed in the 4 d after the shuttle test, and there was a minimum of 7 d of washout between the two experimental blocks (Fig. 1). Participants completed one trial wearing Aquatitan-treated clothing and one wearing a placebo set of clothing allocated in a randomized double-blind manner. The clothing was custom made for the project by Phiten Co. Ltd. (Kyoto, Japan), the manufacturer of Aquatitan. Aquatitan is a suspension of titanium nanoparticles in water (10). To stabilize the Aquatitan particles in the garments, the material was subjected to a cationization process that left a residual electrostatic charge that allowed the titanium particles to bond to the fabric at the targeted titanium concentration. Placebo garments were prepared without Aquatitan treatment. The clothing was tight fitting, 81% nylon/19% polyurethane, black, and covered the entire torso to the neck and the limbs; feet and ankles were covered with tennis-length socks. Participants wore their own untreated singlet and shorts for the baseline measures, after which they wore the allocated clothing for the duration of the shuttle test and the entire recovery period, including all exercise tests and while sleeping. Clean sets of clothing and socks were provided on a daily basis. The blinding code was maintained by an external party. To prevent any possible mixing of clothing sets, clothing was collected, stored, and washed separately.
Placebo Identification Experiment
In the review process, a placebo effect was advanced as a possible explanation for any effect of Aquatitan treatment. A detectable difference in tactile sensation could, in principle, be directly responsible for the effects on the range of motion and performance, simply through improved comfort or through another perceptual mechanism. To investigate a potential placebo effect based on participants using some difference in the feel of the garments to determine the treatment applied, we asked six trained male participants to rate the garments on 200-mm visual analog scales for their assessment of silkiness, coarseness, tightness, goodness of fit, overall comfort, ease of movement, and thermal comfort. Participants were first familiarized with the rating scales while wearing a dummy set of clothing. Participants donned and rated the six sets of clothing applied in a balanced randomized order (Williams design). Participants were exposed to each clothing condition for 6 min and completed sensory ratings at 3 and 6 min (repeated measures). Participants made ratings in three states: blind to the garment treatment, told correctly the garment treatment, and told falsely the garment treatment.
The aerobic power of each participant was measured using a treadmill-based incremental running protocol and direct gas analysis (Moxus Modular V˙O2 system; AEI Technologies, Inc., Naperville, IL). Participants completed a 5-min warm-up at 8 km·h−1 before commencing the test protocol, which started at 10 km·h−1 (0% gradient). Running speed increased by 1 km·h−1·min−1 up to 18 km·h−1 at which point the speed remained constant and the gradient increased at a rate of 1%·min−1, until volitional fatigue. Participants wore a nose clip and gas collection equipment, and HR was monitored throughout all aspects of the test. The V˙O2max of each participant was determined and used to establish individual running speeds for both the shuttle test (using shuttle test software) and the running performance test used during recovery; running speeds were calculated to elicit 50%, 60%, and 70% V˙O2max during the test.
Participants' mass and height were measured before the start of exercising using electronic scales (model UC-321; A&D Co. Ltd., Tokyo, Japan) and a standard laboratory stadiometer (model 26SM; Surgical and Medical Products, New South Wales, Australia). Each participant completed a familiarization session in which each was introduced to all the recovery measures taken in the study (perceived soreness, pressure-pain threshold, joint range of motion, isometric strength, running economy, and run time to exhaustion) and the shuttle test protocol to become used to the running speeds and minimize any learning effect.
Main Trial Procedures
Before beginning each of the two experimental blocks, the participants were required to fast for at least 2 h immediately before the shuttle test and to complete a 48-h dietary record. Participants were requested to replicate their diet before block 1 before block 2, and dietary records were used to confirm this. To further minimize random variation, participants were instructed to maintain normal activity patterns in the week before starting and during the washout period. Participants were also asked to abstain from additional strenuous exercise in the 48 h before the shuttle test.
On arrival at the laboratory on the first day of each of the two experimental blocks, participant's body mass and height were measured, and a preexercise blood sample was obtained from an antecubital vein with the participant in a supine position. For this and other blood samples, blood was collected in serum separation tubes (CAT blood collection tubes, ref 367837; Becton-Dickinson Ltd., Oxford, UK), which were left to stand for 30 min. All blood samples were then spun in a centrifuge (Medifuge; Heraeus Sepatech, Berlin, Germany) at 2000 rpm for 30 min before blood serum samples were dispensed into 1.5-mL Eppendorf tubes and immediately frozen at −80°C before further analysis. Preexercise ratings were collected for perceived soreness and feeling of overall well-being using 11-point linear scales, and participants completed both the daily analysis of life demands of athletes (DALDA) (32) and a short form of the POMS scale, where global mood score is calculated as 100 plus the sum of the five negative descriptors (fatigue, anger, tension, confusion, and depression) minus the positive descriptor vigor (9). Baseline pressure-pain threshold was assessed using a pressure algometer (FPN 100 Algometer Force Gauge; Wagner Instruments, Greenwich, CT) at five different muscle sites on the dominant leg: vastus lateralis, vastus medialis, biceps femoris, and the medial and lateral heads of the gastrocnemius as described by Nussbaum and Downes (26). Isometric strength was evaluated using a Smith machine (Life Core, Auckland, New Zealand) with the bar restrained by connection to a load cell (32×; Rinstrum Pty. Ltd., Queensland, Australia) to assess the maximum force generated during bench press and squat. Bench press force was measured with the upper arm abducted to 90° and flexed 0°, 10°, and 20°; maximum squat forces were measured with internal knee angles of 90°, 105°, and 120°. Joint range of motion in the hip, ankle, and shoulder was measured using a goniometer (Baseline Instruments, Auckland, New Zealand) during the following movements: straight leg raise, hip flexion, leg extension, ankle dorsiflexion, ankle plantarflexion, shoulder abduction, shoulder extension, and shoulder flexion following the methods detailed in Kendall (17). In addition, forced range of motion was assessed for hip flexion and shoulder flexion and extension by using a spring balance to apply an additional 20-N force at the ankle and wrist.
On completion of baseline measurements, the participants completed the shuttle test protocol. Briefly, the shuttle test requires completion of 20-m shuttles at variable intensity including walking, jogging (55% V˙O2max), running (85% V˙O2max), and sprinting undertaken in a repeated sequence with the speeds dictated by audible beeps. Five 15-min blocks of exercise were completed, each followed by a 3-min rest period, giving a total protocol duration of 90 min. To assist in the completion of the protocol, participants were given a commercially available sports drink (Horleys Replace; Horleys, Auckland, New Zealand) before exercise (5 mL·kg−1), during each rest period of the shuttle test (3 mL·kg−1), and immediately after completion of the shuttle test (3 mL·kg−1).
HR was recorded at 5-s intervals using short-range telemetry (Polar 625X; Polar Electro, Kempele, Finland). Subjective perceived exertion and feeling of overall well-being were obtained at set time points during each block of the shuttle test, using 15- and 11-point linear scales, respectively, and 15-m sprint times were recorded using timing lights (5-Channel Timing Lights; Sportstec, Auckland, New Zealand). Ambient temperature, pressure, and humidity were recorded during each trial. Approximately 10 min after the completion of exercise, a venous blood sample was taken from an antecubital vein as described above.
On days 2 and 4, participants returned to the laboratory at the same time of day; a venous blood sample and recovery measures (perceived soreness, feeling of overall well-being, pain threshold, joint range of motion, and isometric strength) were obtained as previously described (Fig. 1). Participants also completed a 40-min moderate-intensity jog set at 50% of their V˙O2max to replicate normal training practice and as a further standardizing feature.
On days 3 and 5, participants returned to the laboratory at the same time of day; once again, a venous blood sample and recovery measures were obtained, and the POMS/DALDA was administered. Participants then completed a treadmill-based protocol designed to assess submaximal running economy and peak running velocity. After a 5-min warm-up at 8 km·h−1, participants completed three 6-min submaximal stages (at 50%, 60%, and 70% of V˙O2max), followed by an incremental increase in running speed (1 km·h−1·min−1) up to 18 km·h−1, at which point the speed remained constant and the gradient increased at a rate of 1%·min−1 until volitional fatigue. The incremental run to exhaustion was chosen because of its high test-retest reliability (coefficient of variation (CV) = 0.8%-1.0%) and because of the association between peak power and competitive performance (14). Online breath analysis was conducted for the final 2 min of each submaximal stage, and metabolic power (J·kg−1·min−1; adjusted for energy equivalent of O2 across the range of the RER) was calculated from the resultant data. Peak velocity was taken as speed at the point of exhaustion, adjusted for the proportion of the final stage completed and gradient, when appropriate, where the equivalent speed on the flat for a given treadmill velocity at percent inclination (i) was treadmill speed × 1.05i.
Serum creatine kinase concentration was measured with a commercially available kit (Roche/Hitachi Total Creatine Kinase kit; Roche, Auckland, New Zealand) using spectrophotometry following the methods described by Szasz et al. (36).
Sample size was generated on the basis of the sufficient power to declare a likely substantial beneficial effect of treatment on performance in our designated primary outcome measure: peak velocity in incremental run. Consistent with our general method, we estimated the sample size by magnitude-based practical inference, with type 1 and 2 error rates of 0.5% and 25%, respectively (13). The smallest beneficial change was set at 0.3 times the average variation in endurance running performance of ∼2.4% (12,14) and with test CV of 1%. Calculations yielded n = 14.
The effect of Aquatitan treatment on outcome measures was estimated with mixed modeling (Proc Mixed, SAS Version 9.1; SAS Institute, Cary, NC). With the exception of noncontinuous and categorical scale data, all outcome variables were log-transformed before modeling to reduce nonuniformity of error and to express outcomes as percentages (13). For the shuttle test, sprint velocity, feeling of well-being, and RPE were determined from appropriate repeated-measures models with sprint and block as nominal coding effects. In this model, random effects (covariance structure) were the between-athlete variation, the additional variation associated with exposure to the treatment, variation between blocks, and variation between sprints (sprint velocity only). Because of the nature of the experimental design, several confounders were identified a priori and were included as covariates within the appropriate models. All covariates were first normalized to and were expressed as a proportion of the within-participant SD for the covariate. For the shuttle test, the relative humidity and the natural log of temperature measured on the day of the trial were included as moderating covariates. Recovery measures were analyzed using five variations. Peak run velocity was determined from a repeated-measures model with laboratory humidity and the natural log of temperature on the day of the test included as moderating covariates; the random effects were the between-athlete variation, additional treatment-associated variation, and variation between days 3 and 5. Exercise efficiency was determined from a linear model, where run velocity was the abscissa numeric predictor. During the recovery period, blood markers, muscle soreness (pressure-pain threshold), isometric strength, HR, feeling of well-being, overall soreness, psychometric parameters, and range of motion were determined from repeated-measures models with the outcome at baseline (before each shuttle test without experimental clothing) as a moderating covariate; random effects were between-athlete variation, treatment-associated variation, and variation between days 2 and 4 or the days 3 and 5 recovery points. Finally, HR during the shuttle test was analyzed overall and by block using a linear model with humidity and the natural log of temperature included as moderating covariates and the random effects were the between-athlete variation and the additional variation associated with exposure to the treatment.
Presentation of data.
Measures of centrality and spread for participants' descriptive variables and scale data are raw means and SD. Spread for log-transformed variables is presented as the CV, which can be converted to the approximate unit value by converting using a factor then multiplying or dividing by the mean. Confidence limits (CL) for the effects derived from back-transformed means are also expressed as percentages, with unit values calculable as above for SD. All data are rounded to two significant figures.
Estimating uncertainty and statistical inference.
In light of limitations associated with P values and traditional hypothesis testing (5,35), we make inferences about the population values of statistics via magnitude-based precision of estimation, as summarized recently in Hopkins et al. (13) and Cohen (5). Precision is presented as 90% CL. After standardization, magnitude-based inferences about the true value for outcomes, except performance, were qualified using a modification of the Cohen effect size classification system (trivial = 0.0-0.2, small = 0.2-0.6, moderate = 0.6-1.2, large = 1.2-2.0, very large = 2.0-4.0, and enormous > 4.0) (3). Using this classification, the threshold for the smallest substantial effect is a standardized difference of 0.2. For performance, we used the effect magnitude thresholds established by Hopkins et al. (13), where magnitude is quantified as the product of the typical error (CV) for the performance measure and qualified within the following effect magnitude thresholds: small = 0.3-0.9, moderate = 0.9-1.6, large = 1.6-2.5, very large = 2.5-4.0, and extremely large > 4.0. The CV for the performance measures were derived from published values of typical error. For the shuttle test, a typical error of 1.9% (24) and the argument by Paton et al. (27) that, on the basis of reaching the ball ahead of an opponent, ∼0.8% is the smallest worthwhile enhancement in sprint speed for football players, led us to take 0.7% (i.e., ((0.3 × 1.9) + 0.8)/2) as the estimate for the small threshold. For peak velocity in the incremental run, we assumed that performance in this test reflects performance in the field (34). We took 2.4% as the variation for running performance (12,14), leaving 0.72% as the threshold for the small threshold. In addition to the sport-specific estimates for the smallest worthwhile effect, we inferred performance outcomes based on the standardized difference. We performed an analysis of the likelihood that a measured increase or decrease is greater than the smallest effect by calculating the probability that the response is substantial from the two-tailed t distribution (SAS code available from authors on request). We ordered probabilities into cutoffs and infer the following: <1% = almost certainly not, 1%-5% = very unlikely, 5%-25% = unlikely, 25%-75% = possible, 75%-95% = likely, 95%-99% = very likely, and >99% = almost certain. In the case where most (>50%) of the uncertainty lies between the threshold for a substantially positive and negative effect, the likelihood of the effect being trivial (negligible) is qualified. Effects were described as unclear or inconclusive if the confidence interval overlapped into both positive and negative values.
Effects of Aquatitan-Treated Garments on Shuttle Test Performance
After adjustment for small daily variation in environmental conditions (19.5°C ± 1.0°C and 54% ± 8% relative humidity), overall sprint times during the shuttle test were faster with Aquatitan treatment, but the magnitude was likely trivial (Table 1); when evaluated as a standardized difference, the magnitude of the effect was also trivial (0.9; ±90% CL = ±0.12). Overall sprint times were 1.7% (±0.8%) faster in experimental block 2 compared with that in block 1. Runners tended to report lower overall RPE during the shuttle test with Aquatitan treatment, but there was no clear effect on feeling of well-being (Table 1) or on exercising HR (−0.01% ± 2.89%).
Effects of Aquatitan-Treated Garments on Subsequent Run Performance and Measures during Recovery from the Shuttle Test
Subsequent run performance, exercise efficiency, and metabolic response.
Aquatitan treatment led to a possible small reduction in peak run velocity of 1.1% (±1.6%, magnitude-based likelihoods of harm/trivial/benefit = 68:30:2) on day 3, but a likely small increase of 2.0% (±1.6%, likelihoods = 0.2:7.9:92.0) on day 5 (Fig. 2). The combined mean effect of Aquatitan treatment on incremental run performance on days 3 and 5 was an inconclusive, although most probably with a trivial benefit of 0.43% (±1.3%, likelihoods = 6:59:35). In the standardized difference, the respective treatment effects on days 3 and 5 and combined were −0.16 (±0.23, possibly trivial), 0.29 (±0.24, small increase likely), and 0.06 (±0.18, likely trivial). Wearing Aquatitan was associated with possible small reductions in metabolic power (increased efficiency) during submaximal running on days 3 (−2.0% ± 3.1%) and 5 (−2.2% ± 3.1%). There was no clear effect on the RER (not shown).
Range of motion.
Overall, Aquatitan treatment led to small increases in most of the range of motion parameters assessed, although there was some variability between days within and between movements (see Figure Supplemental Digital Content 1, http://links.lww.com/MSS/A31 and Table Supplemental Digital Content 2, http://links.lww.com/MSS/A32 which provide the statistical summary of the effect of Aquatitan on individual joint range of motion during the 4-d recovery from the shuttle test). At the hip joint, likely increases were seen in straight leg raise and voluntary hip flexion on days 2-4, but increases in forced hip flexion were possibly small on day 2 and possibly trivial on days 3-5. Increases in ankle plantarflexion were observed on days 2 (possible) and 5 (almost certain), but the increases on days 3-4 were possibly trivial. Effects on ankle dorsiflexion were possibly or likely trivial. At the shoulder joint, a small possible increase was observed in abduction on day 2, but the effect on the other days were likely (day 3) or possibly trivial. Very likely, small increases in voluntary extension were seen on days 2 and 3, but increases were possibly trivial on days 4 and 5. Possible to almost certain small increases were observed for voluntary and forced shoulder flexion on all days, with the exception of a possible trivial response for flexion on day 5 (Supplemental Digital Content 1, http://links.lww.com/MSS/A31). Aquatitan treatment had no effect on the forced voluntary difference at the hip and shoulder (Supplemental Digital Content 2, http://links.lww.com/MSS/A32).
In the control condition, creatine kinase activity increased 1.3-fold from baseline (back-transformed mean = 222 ± 199 U·L−1) on days 2 and 3, respectively; at these times, there were possible small increases with Aquatitan (standardized difference: 0.25 ± 0.35 and 0.23 ± 0.34); the effects immediately after shuttle test and on days 4 and 5 were possibly trivial.
The overall reduction in perceived soreness in response to Aquatitan treatment during recovery was possibly trivial (−0.3 ± 0.3 scale units), although it is noteworthy to report very likely (−0.8 ± 0.5) and possible reductions (−0.3 ± 0.5 and −0.3 ± 0.5) on days 3, 4, and 5, respectively. Outcomes for pressure-pain threshold were of a negligible magnitude and inconclusive (not shown).
Collective results of DALDA, POMS, and feeling of overall well-being assessments during recovery suggest that some psychological benefit under Aquatitan treatment is possible. On day 3, participants reported substantially lower negative DALDA symptoms of stress (−1.2 ± 1.0 scale units), coupled with likely elevations in POMS anger and esteem (1.0 ± 0.8 and 1.3 ± 1.3 scale units, respectively), and possible elevations in vigor and tension (1.2 ± 1.8 and 1.2 ± 1.4, respectively). Moreover, participants reported elevated feeling of overall well-being under Aquatitan treatment on days 3 (0.5 ± 0.6, possible) and 4 (0.6 ± 0.6, likely), but outcomes were unclear on days 2 and 5. No clear effects were noted for any psychological parameter on day 5.
Aquatitan treatment showed a small possible improvement in performance during the squat exercise at 90° (10% ± 8%) and 105° (11% ± 9%) knee angle 24 h after the shuttle test; all other outcomes were likely trivial (data not shown for brevity).
When blinded to the treatment, participants perceived a possible small reduction in silkiness (standardized difference = 0.25 ± 0.43) and increase in coarseness (0.41 ± 0.59) while wearing the Aquatitan-treated garments. When informed of the treatment, the reduced perception of silkiness increased in both identity conditions (treatment correctly identified = −0.95 ± 48, treatment falsely identified = −0.83 ± 0.47), although for coarseness, perception was increased when treatment was identified falsely (0.78 ± 0.61) but remained small when treatment was identified correctly (0.44 ± 0.59); participants could not identify the true-false identity for silkiness (−0.12 ± 0.61), but for coarseness, perception when told and blinded was not clearly distinguishable (0.03 ± 0.83). In addition, when blinded to Aquatitan treatment, there were small reductions in the perception of ease of movement (−0.38 ± 0.32) and thermal comfort (−0.42 ± 0.37) and a possible reduction in tightness (−0.24 ± 0.29). When informed of the treatment, the reduction in ease of movement remained small (−0.25 ± 0.32) but became trivial when the clothing condition was identified falsely (0.15 ± 0.32). Conversely, thermal comfort was perceived as being higher with Aquatitan (treatment correctly identified = 0.58 ± 38, treatment falsely identified = 0.35 ± 0.37) and the true − blind difference was large (1.0 ± 0.6). Differences in perception of goodness of fit were trivial, and there was a possible small reduction in overall comfort with Aquatitan treatment in the blind condition (−0.31 ± 0.40).
The purpose of the study was to determine the effects of Aquatitan-treated garments on performance, muscle pain and tension, and markers of muscle damage after a prolonged intermittent shuttle test exercise (designed to simulate soccer/hockey match play). We report that the improvement in overall repeated sprint velocity during the shuttle test in response to Aquatitan treatment is most likely to be of trivial consequence to sprint speed in match play. During recovery, wearing of Aquatitan-treated garments increased voluntary joint range of motion in the shoulders, hips, and ankles, and there was some evidence of a possible benefit to psychological status and bodily soreness on day 3 and on running efficiency on days 3 and 5. The possible small reduction in peak running velocity on day 3 with Aquatitan clothing was contrasted by a likely small increase on day 5 to yield a combined inconclusive, although most probably trivial, outcome for the effect of Aquatitan on recovery performance.
An interesting finding was that the small effect of Aquatitan on voluntary range of motion might indicate a change in one or both of the contractility of the agonist muscles and the extensibility of the muscle-tendon complex in the antagonist muscles. However, we considered the change in forced range of motion to be indicative of the change in the extensibility of the muscle-tendon complex in the antagonist muscles. Because the improvements in both voluntary and forced absolute range of motion were largely of similar magnitude, and any difference in the magnitude of the effect of treatment was trivial (Supplemental Digital Content 2, http://links.lww.com/MSS/A32), it seemed likely that the compliance of the tendon or muscle-tendon complex was affected by Aquatitan. In other words, the increased range of motion indicated that tendon stiffness was reduced by Aquatitan treatment, meaning that the tendon exhibited increased mechanical strain for a given mechanical stress. The probable action on muscle-tendon complex stiffness was confirmed by the absence of clear substantial effects on isometric strength, blood creatine kinase, and the pressure gauge estimate of muscle soreness.
Tendon stiffness has been proposed to be the most important property for transmitting muscle tension to skeletal parts during posture and movement (28), and it is well known that reduced muscle-tendon complex stiffness is associated with improved performance and increased potentiation of action via the stretch-shorten cycle (4,20-22). In human running, motion is, in part, maintained by storage of energy in tendons during the eccentric or loading phase of ground contact, which is returned during the concentric phase of ground contact (33). In simple terms, the energy stored depends on tendon compliance (the reciprocal of stiffness) at a given load, and so reduced stiffness will result in enhanced energy storage under the same external load (33), which has been linked to improved endurance and sprint running performance (33). In support to this, we observed a possible improvement in running efficiency with Aquatitan treatment consistent with improved energy storage and return. However, the present improvement in the extensibility of the tendon/connective tissue induced by the Aquatitan treatment was insufficient to result in a consistent substantial increase in performance in the present experimental model. Nonetheless, reduced stiffness of the muscle-tendon complex may be associated with a reduced likelihood of injury in activities such as running because the ultimate tensile stress of the muscle-tendon complex will only be reached at an extreme range of motion (20). However, the occurrence of traumatic injury to joints could be adversely affected if ligament stiffness was also reduced because this would allow joints to displace substantially at lower external loads.
We report that the magnitude of the effect of Aquatitan on repeated sprint performance in the shuttle test and subsequent peak run velocity was, overall, trivial. By magnitude-based inference, the threshold value selected for the smallest worthwhile effect has a defining effect on the inferential outcome. Hopkins et al. (11) estimate that, in elite athletes, a treatment must elicit a shift in performance of at least 0.3 times the CV of performance in the event to register as worthwhile. It is difficult to detect any worthwhile changes due to an intervention in team sport matches because of the effects of tactics and variability on physical work rate and distance covered, and for this reason, the CV for performance in match play simulation shuttle run tests is the current best reference. In human running, peak velocity in an incremental test is analogous to peak power, and peak power predicts field time trial performance time (34). However, CV-derived estimates for the smallest important effect in well-trained subelite team sport athletes (present sample) may not necessarily reflect the figure for all team sport athletes, so the standardized difference provided us with an inferential default. Likewise, the SD of our subjects may not necessarily reflect the figure for the range of elite or recreational male team sport athletes (we excluded female athletes for brevity), and this will affect the magnitude of the standardized difference. For example, mean shuttle run repeated sprint SD expressed as a percentage of the mean in top professional and amateur soccer players were 2.4% and 3.3%, respectively (15), and in well-trained (V˙O2max 59 mL·kg−1·min−1) amateur game players, this was 4.3% (24); in recreational soccer players, values of 12.7% (18) and 12.3% (25) were available. Using these SD, the standardized effect of Aquatitan would be possibly small for professionals (0.29 ± 36, likelihoods = 1.5:31.5:67) but almost certainly trivial for recreational players (0.06 ± 0.07). For peak incremental run performance, the SD was 10.5% in 50 national-league soccer players (29) and 5.0% in 74 recreational athletes from mixed sports. In the standardized effect, these estimates yield, for the day 3/day 5/overall, respectively, likely/possibly/very likely trivial outcomes for the elite but, analogous to the outcome for the present data, possibly harmful/likely beneficial/likely trivial outcomes for recreational athletes. Hopkins et al. (13) suggest that, when making a clinical or practical inference, a likelihood of benefit of >25% is of interest, but if the chance of serious harm is >0.5%, then the treatment should not be pursued. However, for nonlethal interventions with the potential to enhance athletic performance, 0.5% is too conservative, and the chance of a small decline in performance of <1%-5% is probably acceptable to most athletes particularly when considered against the likelihood of benefit, e.g., for the scenario for professionals above: benefit-to-harm ratio = 45:1. Therefore, a worthwhile benefit to high-intensity repeat sprint performance for professionals remains a possibility and is worthy of research to clarify; however, a trivial outcome is more likely for subelite and recreational team sport players. Of interest at this point in the discussion is the serum creatine kinase activity outcome. Although an insensitive and indirect measure, a small elevation was possible with Aquatitan during the first 48 h of recovery, which is in line with the pattern for reduced sprint times in the shuttle test; that is, a faster sprint velocity would have possibly increased muscle damage as a result of larger eccentric forces. Greater damage at 48 h might have contributed to the tendency for worse performance with Aquatitan on day 3.
It has been suggested that Aquatitan garments and skin adhesive tape may reduce pain sensation and pain memory via an influence on peripheral sensory neurons and/or central processing. In support of this concept, Korte (19) provided experimental evidence that Aquatitan treatment could alter synaptic plasticity, resting membrane potential, and firing of pyramidal neurons of the mouse hippocampus toward a condition suggestive of reduced pain memory and analgesia. In support of a sedative effect of Aquatitan, Aoi et al. (1) found evidence for reduced sympathetic and increased parasympathetic activity in mice. In the present study, we chose an intensive exercise stress known to result in elevated markers of muscle damage and DOMS (18), but we observed mixed outcomes with respect to the effect of Aquatitan on perceived sensation of tissue soreness and psychometric status. There were patterns in the data set toward a possible small favorable effect on overall feeling of well-being on days 3-4 and on mood status on day 3. These observations could be associated with a mechanism of action at the cellular or neurotransmitter level, as suggested above or be linked to perceivable differences in garment feel that might trigger a placebo effect, although the differences in garment feeling of silkiness, coarseness, ease of movement, and thermal comfort when blinded to the condition would be viewed as less favorable perceptions expected to negatively influence outcomes. These effects will only be clarified or eliminated as possible physiological explanations through additional studies.
In conclusion, Aquatitan-treated garments are unlikely to provide substantial benefit to running performance in recreational or subelite team sport athletes, but further investigation into repeated sprint performance in elite may be warranted. Future studies could also further characterize and determine the practical consequence and mechanism behind improved tendon compliance and the possible enhancement of psychological state during recovery that occurred when wearing Aquatitan garments.
Funding assistance for the study was provided by Phiten Co. Ltd., Kyoto, Japan. The assistance of Jacques Rousseau, Andy Hollings, Andre Nelson, Jamie Stewart-McDonald, and Dr. Ajmol Ali is gratefully acknowledged.
The authors also thank the valuable comments and suggestions of the reviewers.
The results of the study do not constitute endorsement by the American College of Sports Medicine.