Recent position statements by the American College of Sports Medicine (ACSM) (1) and the National Athletic Trainer's Association (NATA) (6) summarize the physiologic, medical, and performance considerations associated with dehydration. In extreme cases, severe dehydration may lead to heat stroke and possibly death. During the 1997-1998 wrestling season, 3 collegiate wrestlers died while attempting to ‘make weight’ by starvation and thermal dehydration through perspiration which resulted in hyperthermia (7). Effective with the 1999 wrestling season, the National Collegiate Athletic Association (NCAA) adopted new regulations associated with weight loss by establishing a Wrestling Weight-Certification Program (WWCP) to ensure the health and safety of wrestlers (8,17,24).
Both the NCAA and the National Federation of State High-School Association (NFHS) have included rules that require the assessment of hydration status among wrestlers before establishing a minimum wrestling weight (8,25). Collegiate and high-school wrestling is the only sport in the USA that mandates the measurement of hydration status before competition. The aim of the hydration assessment as part of the WWCP is to ensure that wrestlers are euhydrated at the time of weight certification. The NCAA has chosen a urine specific gravity (U sg) measurement of ≤1.020 to identify a state of euhydration (8,17), whereas at the high-school level, this threshold may be as high as 1.025. Collegiate wrestlers that have a U sg > 1.020 are not permitted to have their body composition assessed to determine their minimum wrestling weight. Previous research has questioned both the validity of U sg as a satisfactory measure of hydration status (18) and the recommended U sg limit of 1.020 as a euhydration-status indicator (16) in collegiate wrestlers in both laboratory- and field-based settings. In the studies of Oppliger et al. (16) and Popowski et al. (18), U sg was sensitive to changes in hydration status but lagged behind plasma osmolarity (P osm) during periods of rapid body fluid turnover and therefore correlated only moderately with P osm during acute dehydration. Recently, Bartok et al. (4) has reported poor correlations between weight loss by dehydration and U sg in collegiate wrestlers. Given that U sg lacks the precision necessary to meaningfully predict the extent of dehydration (3,15) coupled with the cost, invasiveness, and impracticality of blood measures such as P osm, the need for a simple noninvasive field measure of hydration status is clearly warranted for the wrestling community and other sport settings.
The relationship between ultrasound speed and hydration status of soft biological tissue, including muscle, has been evaluated in a number of investigations including: ex vivo animals (19,21), in vivo animals (9), human muscle edema (22), and simulated hypergravity-induced dehydration in humans (10). Ultrasonic method for tissue water content monitoring is based on the premise that ultrasound velocity through soft tissue is a linear function of the tissue water content (19). Most soft tissues, including muscle that consists of ∼73% water (28), exhibit a shift of the ultrasound velocity (UV) associated with the change in their water content (19). In a recent study by Topchyan et al. (22), it was reported that in chronic renal patients before and after hemodialysis, UV increased by 5 m·s−1 in the soleus muscle after a weight loss of 3.8 kg or 5% of body mass (BM). Sarvazyan et al. (19) have reported in ex vivo animal tissues that a 1% loss of water content in lean muscle tissue produces ∼a 3.5-m·s−1 increase in UV. Silverman et al. (21) reported that ultrasound speed decreased from 1,605 m·s−1 (normotensive medium) to 1,563 m·s−1 in suspended bovine cornea after swelling was induced by decreasing medium tonicity. To our knowledge, no studies have investigated the use of UV to detect changes in the hydration status of wrestlers during periods of acute dehydration and rehydration. In a recent review of concerns and issues relating to hydration testing of athletes, it is recommended that additional research is clearly needed on new indices and methods to accurately assess the hydration status of athletes particularly in a field setting (15). This issue has direct application to the mandated hydration testing that occurs before the minimal wrestling weight certification as part of a WWCP.
The purpose of this study was to evaluate the utility of UV to detect changes in the hydration status of wrestlers after undergoing acute dehydration and a 2-hour rehydration period. Hydration status was quantified by measuring changes in P osm, U sg, urine osmolarity (U osm), and BM. We hypothesized that UV would be able to detect changes in hydration status of collegiate wrestlers undergoing acute hypertonic dehydration. Confirmation of the ultrasonic approach using a convenient, hand-held device may have direct application toward the administration of the NCAA and NFHS hydration rules in the sport of wrestling and also other sports in which weight loss and dehydration associated health risks are prevalent.
Experimental Approach to the Problem
The specific aim of this study was to evaluate the utility of UV to detect changes in the hydration status of NCAA wrestlers after undergoing acute dehydration and a 2-hour rehydration period. Hydration status was quantified by measuring changes in P osm, U sg, urine osmolarity (U osm), and BM all of which are considered standard laboratory indices (1). The research experiment followed a repeated-measures design in which each subject served as their own control. Subjects reported to the Appalachian State University (ASU) Human Performance Laboratory once for orientation and later that same day for subsequent measurements of UV, P osm, U sg, U osm, and BM during the dehydration and rehydration trials.
NCAA wrestlers (N = 47) who competed on the ASU (Boone, NC, USA) and Belmont Abbey College (Belmont, NC, USA) wrestling teams during the 2008-2009 season participated in this study. Subject characteristics were as follows: (mean ± SEM); age 19.1 ± 0.2 years, height 1.73 ± 0.1 m, BM 79.4 ± 2.4 kg, percent body fat (%BF) 15.0 ± 1.1%, and average duration of wrestling experience was 7.3 ± 3.4 years. The ASU wrestling program competes at the NCAA Division I level and Belmont Abbey College at NCAA Division II level. Both teams were tested in the month of October, which is considered preseason at both levels from training-status perspective. Subjects were representative of all 10 collegiate weight categories. Written informed consent was obtained from all subjects before they were allowed to participate in the study, and all experimental procedures were approved by the Institutional Review Board for investigations involving human subjects at ASU.
Subjects were instructed to report to the laboratory in a euhydrated state, which was confirmed through blood and urinary measures. During orientation, subject demographic data (height, BM, and body composition) were obtained; subsequent urinary and blood samples were collected. Body composition was assessed from a 3-site skinfold (triceps, subscapular, and abdominal) test using a Lange skinfold caliper (Cambridge Scientific Industries, Inc., Cambridge, MD, USA). Body density (D b) was determined from the 3 skinfold measures using the prediction equation D b = [1.0982 − (sum skinfolds) × 0.000815] + [(sum skinfolds)2 × 0.00000084] validated by Lohman (11). Percent BF was determined from D b using the Brozek equation (5). Each urine sample was collected in an inert polypropylene container. The U sg measurements were determined by an optical refractometer (NSG Precision Cells Inc., Farmingdale, NY, USA). A total of 4 blood samples were obtained during each trial, from the median cubital vein, on the anterior forearm via certified phlebotomists. Blood, urine, and UV measures were taken predehydration, postdehydration, and at 60 and 120 minutes during a 2-hour rehydration period. The predehydration (baseline) samples were taken 1-hour before the dehydration period. Urine osmolarity (U osm) and plasma osmolarity (P osm) were determined via freezing-point depression in triplicate using an osmometer (Model 3250, Advanced Instruments, Inc., Norwood, MA, USA) calibrated to the manufacturer specification. Each participant was provided a minimum weight loss goal of a 3% reduction in BM. A 3% decrease in BM was chosen because this represents the typical amount of dehydration that occurs in the sport of wrestling in the 24-hour period before competition (17). Controlled acute dehydration was achieved during a 2-hour standard wrestling practice regime that normally occurs during the competitive season. The wrestling practice regime consisted of a combination of calisthenics exercises, active technical drilling, and live wrestling scenarios. We have employed this dehydration paradigm in previous published studies (26). After successful completion of dehydration, a second measure of BM, U sg, U osm, P osm, and UV was assessed.
During the 2-hour rehydration period, subjects were instructed to drink a carbohydrate-electrolyte solution (6%, or 60 g·L−1) (Gatorade®, Barrington, IL, USA). The carbohydrate-electrolyte beverage contained 20 mmol·L− 1 of sodium and 3.2 mmol·L− 1 of potassium. Research assistants provided all beverages to the subjects. During the first 20 minutes of their rehydration period, the subjects consumed a beverage equal to one-half of their BM loss. From 20 to 40 minutes into the 2-hour rehydration period, subjects consumed a second volume of beverage to replace the remaining 50% of their BM loss. The third and fourth blood, urine, and UV measures were obtained at 60 and 120 minutes into the rehydration period.
Ultrasound velocity was measured by an ultrasonic probe interfaced to a data acquisition unit managed by a PC (Artann Laboratories, Trenton, NJ, USA). The hand-held ultrasonic probe (Figure 1) was an updated version of the equipment described by Topchyan et al. (22). The human soleus muscle was chosen as the study object because of its size, relatively uniform tissue content, and convenient in situ access (22). The hand-held device consisted of 2 probes that could be adjusted to fit around the back of the subject's calf. The probes were slightly lubricated with acoustic gel and then placed on each side of the subject's soleus muscle. The measurement site was located in the upper part of the calf, at 2/5 of its length from the tibia-femur joint to the middle of the ankle and in the middle of the posterior part of the calf cross-section (22). The measurements were taken in triplicate at each time. Each measurement was taken while the subjects were sitting and in a relaxed muscle state and took approximately 5 seconds to complete. The probes were pressed inward until the device gave recognition that an appropriate current was being sent through the muscle. Once the device signaled it was ready, the researcher pulled the trigger of the device to record a UV measurement in meters per second (m·s−1). Ultrasound velocity was calculated from the measured values of the acoustic base between emitting and receiving transducers and the propagation time of the ultrasonic pulse-a 1 MHz 1.5-microsecond long tone burst modulated by Gauss envelope. The transmitted and received signals were digitized with sampling of 0.05 microseconds. The measurements were taken in triplicate at each time of the 4 time points. Each measurement was taken while the subjects were sitting and in a relaxed muscle state.
Values are expressed as mean ± SEM. Dependent variables were analyzed using a 1-way repeated-measures analysis of variance. Significant main effects were evaluated with paired t tests using a Bonferroni adjustment, with statistical significance set at p ≤ 0.025. Pearson product-moment correlations between markers of hydration status and UV were evaluated at each of the time points throughout the investigation. Significance was set at p ≤ 0.05 for all variables in the correlation analysis.
Subjects dehydrated to achieve an average BM loss of 3.6 ± 0.14%. Body mass changes (kg) throughout the study were as follows: Predehydration (baseline) = 79.4 ± 2.4, Postdehydration = 76.7 ± 2.4, and 2-hour rehydration = 78.9 ± 2.4. For rehydration, subjects were provided with beverage amounts equal to 100% of their BM loss. Subjects were able to regain 2.8 ± 0.14% of the BM loss during the 2-hour rehydration period.
Ultrasound velocity significantly increased (p < 0.001) from predehydration (1,583.07 ± 0.8 m·s−1) to postdehydration (1,585.26 ± 0.9 m·s−1) and then returned to baseline at the 2-hour rehydration time period (1,582.74 ± 0.9 m·s−1) (Table 1 and Figure 2). At both the 1- and 2-hour rehydration time points, UV was significantly different from the postdehydration time point (p < 0.001). Individual responses to UV throughout the dehydration and rehydration trials are depicted in Figure 3.
Significant main effects (p < 0.001) were found for U sg, U osm, and P osm. P osm increased incrementally from the predehydration (295.6 ± 0.8 to 303.0 ± 1.7 mOsm·L−1) at the 1-hour rehydration time point and then returned to below baseline at the 2-hour rehydration time point (292.3 ± 1.3 mOsm·L−1) (Table 1 and Figure 2). Similar results were found with both U sg and U osm. U osm increased from predehydration (688.5 ± 47.4 mOsm·L−1) to postdehydration (778.0 ± 31.9 mOsm·L−1) and then returned to below baseline at the 2-hour rehydration time period (442.6 ± 52.5 mOsm·L−1) (Table 1 and Figure 2). U sg also increased from predehydration (1.018 ± 0.001) to postdehydration (1.024 ± 0.001) and then returned to below baseline at the 2-hour rehydration time period (1.013 ± 0.002) (Table 1 and Figure 2). The change in P osm from the 1- to 2-hour rehydration time period significantly correlated to the change in UV during the same time period, (r = 0.27, p < 0.001). No correlations were found between P osm and UV from the predehydration to postdehydration time periods.
To our knowledge, this is the first study to investigate the use of UV as a potential noninvasive marker of whole-body hydration during acute hypertonic dehydration and rehydration in wrestlers. Results from this investigation demonstrated significant changes in UV during periods of dehydration (BM change = −3.6 ± 0.14%) (UV=+2.18 m·s−1) and rehydration (BM change = +2.8 ± 0.12%) (UV = ·−2.89 m·s−1) in male collegiate wrestlers. Similar significant changes in P osm, U sg, U osm, and BM were also found. Dehydration of 2-3% of BM can compromise heat dissipation, cardiovascular function, and exercise performance (1,2). For the purpose of a WWCP, acute dehydration by 3% of BM can also result in a significant underestimation of minimal wrestling weight (4). An underestimation of minimal wrestling weight suggests that the athlete can safely lose more weight, but in reality, this may lead to unhealthy and potentially dangerous weight loss. Therefore, for a marker of whole-body hydration to be of use in a WWCP, it should be able to identify losses of total body water equivalent to ∼3% of BM.
The measured values of UV in a hydrated and dehydrated state were in the range of 1,559-1,597 m·s−1, which generally conforms to the known range of UV in muscle (13,19,22,23). The mean UV in the present study of college-aged wrestlers (19.1 ± 0.2 years) in a hydrated state was 1,583 ± 5.3 m·s−1, which is consistent with a previous study of 26 subjects (age range of 15-25 years) which reported a UV of 1,579 ± 16 m·s−1 also measured in the soleus muscle (22). Topchyan et al. (22) have also found that on average male subjects have velocities of more than 20 m·s−1 (∼1.5%) greater than that of female subjects. One possible explanation for this finding may be the generally higher fat content in skeletal muscle of legs of women that results in the proportional decrease of the velocity in the muscle tissue (14).
The increase in UV in a dehydrated state found in the present study is consistent with that of previous investigations that have evaluated velocity in both in vivo human muscle edema (22) and ex vivo animal tissue (19,21). In the study by Topchyan et al. (22), which investigated chronic renal patients before and after hemodialysis, UV increased by 5 m·s−1 in the soleus muscle after a weight loss of 3.8 kg or 5% of BM. Results are similar to that of Topchyan et al. (22) in that subjects of the present study lost an average of 3.6 ± 0.14% of BM and UV increased by +2.18 m·s−1. The results of the present study coupled with those of Topchyan et al. (22) suggest that independent of the method used to induce dehydration (i.e., hemodialysis or acute hypertonic dehydration), a corresponding increase in UV can be detected. However, both the present study and the results of Topchyan et al. (22) are considerably lower than what has been previously reported in ex vivo animal tissues in which a 1% loss of water content in lean muscle tissue produces ∼a 3.5 m·s−1 increase in UV (19). It has been suggested that ex vivo muscle tissue maintains a rather stable homeostasis of liquid balance, and thus may be a poor indicator of changes in total body water content (22).
The significant changes in UV were also accompanied by similar responses in P osm, U sg, U osm, and BM. In addition, the change in UV significantly correlated (r = 0.27, p < 0.05) with the change in P osm during the 1- to 2-hour rehydration period; however, no correlations were found between UV and P osm during the euhydration to postdehydration time period. The responses of P osm, U sg, and U osm to progressive dehydration and rehydration are similar to other investigations that have employed similar protocols (16,18,27). In these investigations, P osm shows a stair-step increase with dehydration and a return toward euhydration during the recovery period. Of interest in the present study is that the P osm continued to rise at the 1-hour rehydration period to over 300 mOsm·L−1, which has also been reported in previous investigations (20,27). It is generally accepted based on previous research (12,20,29) that after ingesting a carbohydrate-electrolyte beverage, P osm will return to baseline values after a 2-4 hour period after acute dehydration. The results of the present investigation coupled with others (4,16,18,27) suggest that P osm, U sg, and U osm, are all sensitive to changes in acute hypertonic dehydration and rehydration in wrestlers. In addition, significant changes in UV were detected with a corresponding decrease and subsequent increase in BM by ∼3.0%.
Results of the study demonstrated that changes in UV reflect the changes of P osm, U sg, U osm, and BM during acute dehydration and rehydration in collegiate wrestlers. The present study should be considered as a preliminary investigation into the utility of UV to detect changes in the hydration status of wrestlers/athletes in a field setting. The use of UV may have practical application, as an alternative method to U sg, in a WWCP in which the athletes are required to have hydration assessed before competition.
As discussed in the ACSM (1) and the NATA (6) position stands, there are sound physiological and medical reasons for screening, detecting, and minimizing dehydration in athletic populations. This is the case for athletes that experience dehydration either intentionally or involuntarily. As discussed in the case of the 3 collegiate wrestlers, the risks associated with dehydration can be fatal and therefore offer a rationale for a simple noninvasive field test of hydration status in athletes. In contrast to other field measures to assess hydration such as U sg, UV does not require a biological sample and provides quantitative data in a rapid, noninvasive way. Future research with UV for the purpose of assessing hydration status should be evaluated in combination with measures of total body water in both laboratory- and field-based settings. In addition, future research with other wrestling and athletic populations is clearly warranted.
This work was funded by Crayhon Research, Inc., Reno, NV. The results of the present study do not constitute endorsement of any product by the authors or Appalachian State University.
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