Compression stockings (CS) have traditionally been designed for and used by populations suffering from venous return insufficiency (VI) secondary to a number of diseases or disabilities (20,22) or at risk for developing deep vein thrombosis (23). Compression stockings enhance the skeletal muscle pump function thereby increasing blood circulation back to the heart from the limbs. Lower extremity CS act on the calf muscle pump (capable, in healthy individuals, of generating pressures of greater than 200 mm Hg) and promote even greater venous return than normal conditions (4).
Numerous studies have illustrated the benefits of CS in rehabilitation settings and among those suffering from VI (6,19). However, there is a relatively new interest in using CS in athletics. Compression stockings and other compression garments have been tested among a diverse population of athletes (10–12,15,16). Some CS manufacturers claim that similar benefits of CS experienced among chronic disease and/or disability patients (improved venous return, improved circulation, decrease in leg soreness, and swelling) can be of use to athletes, particularly endurance runners (24). Consequently, CS have been marketed as a way to reduce lactic acid buildup in the legs during exercise while improving energy, performance, and recovery (24).
Despite manufacturers' claims and the growing popularity among runners, there have been few studies examining the effect of CS on running performance specifically (8,15). These studies have examined both standard (8) and graduated CS (15). Whereas standard CS exert constant pressure, graduated CS exert varying levels of compression. Typically, greater pressure will be applied distally (in or towards the ankle) with less pressure applied towards the calf. This is done to reduce blood pooling in the lower extremities and enhance venous blood return towards the heart. Many factors affect running performance and, historically, one of the more controversial and misunderstood factors has been blood lactate (BLa) and the concept of the lactate threshold (LT) (13). Various training techniques and plans have centered on the premise of delaying the onset of the LT to improve running performance.
Previous studies exploring the relationship between CS and exercise have shown modest improvements in performance and other physiological variables (1,5,8,15,27), however, only one found a significant difference in BLa levels (5). Also, none of the previous studies examined a group of highly trained runners with a homogenous training regimen to help limit variability between runners. If CS were shown to lower BLa levels and delay the LT, their use as an ergogenic aid among professional, amateur, and recreation runners would be substantial. However, currently the literature on the effect of CS on BLa and LT remains unclear, and when considering truth in marketing of CS to runners, ample research and investigation of manufacturers' claims should be well documented.
Therefore, the purpose of this study was to determine whether wearing below-the-knee graduated CS with a minimum of 15 mm Hg of pressure during a maximal treadmill run would induce physiological changes among collegiate cross-country runners. The main outcome variable examined was BLa levels and the corresponding LT. Secondary variables that were assessed were: maximal oxygen consumption (V[Combining Dot Above]O2max), rating of perceived exertion (RPE), heart rate (HR), respiratory exchange ratio (RER), and time to fatigue (TTF). It was our hypothesis that the CS would decrease BLa accumulation, and as a result improve performance during a maximal treadmill test.
Experimental Approach to the Problem
This study used a randomized crossover design to determine the effect of wearing beneath-the-knee graduated CS on BLa, LT, and other physiological markers and running performance in Division III collegiate cross-country runners. This within-group subject study design let each participant serve as his/her own control.
Ten Division III cross-country runners were recruited, (men; n = 7) for this study. All participants were at least 18 years of age, were current members of their collegiate cross-country team, had competed in the previous cross-country season, and all were medically cleared for participation in cross-country competition. None of the female participants reported that they were pregnant. Testing was completed in June and all of the participants were involved in the cross-country off-season conditioning program. All participants were cleared using the American College of Sports Medicine absolute or relative contraindications to testing and criteria for stopping an exercise test (26). All study participants gave written informed consent, and the study was approved by the university institutional review board.
The study used a randomized, crossover design with half of the subjects completing condition 1 first. All participants were asked to report to the laboratory for 2 visits, which were exactly 7 days apart. During visit 1, participants were randomized to group 1 or group 2. Group 1 wore the CS during their first visit, whereas the group 2 wore CS for visit 2. Athletic Recovery Graduated Compression Stockings from SIGVARIS Inc. (Peachtree City, GA, USA) were used. They were made up of 67% dri-release polyester, 26% nylon, and 7% spandex. Each CS was manufactured to provide a minimum of 20 mm Hg pressure (ankle) to 15 mm Hg pressure (calf), when properly fitted (Michael Leonard, personal communication, October 8, 2010). The fitting scale corresponded to each participant's shoe size.
All participants reported at the same time of the day for each of the 2 test days, which varied by individual. This was a performance test and, as such, the participants were instructed to prepare as they would for a race. To best control for nutrition, the participants were not restricted to a specific prerace meal, but were asked to eat a similar (if not identical) meal before each test. Participants were allowed to hydrate ad libitum before testing. Additionally, participants were asked to wear the same clothing and running shoes for each visit.
Before beginning the test, a number of pre-exercise measures were taken. Participants' height and weight were measured using a standard stadiometer and physician beam balance (Table 1). The participants then were seated for 5 minutes during which time the “6–20 RPE Borg” scale (7) was explained to them. The participants were informed that if they needed to stop for any reason during the test, to grab onto the treadmill handrails. This would serve as the volitional sign to end the test. Each participant was fitted with Hans Rudolph (Hans Rudolph Inc.) valve and a Polar heart rate monitor (Polar USA, Lake Success, NY, USA) and either CS or no CS (depending on their condition order). Expired gases were collected and analyzed to calculate oxygen consumption using a ParvoMedics True One system (Sandy, UT, USA) (3). The metabolic measurement system was used to compute V[Combining Dot Above]O2 and RER, and data were consolidated and reported in 30-second increments.
After 5 minutes of seated measurements, the participant then stepped onto the treadmill and began a walk at 80.4 m·min−1 with a 0% incline. While walking at 80.4 m·min−1, HR and RPE were recorded. The BLa was measured through finger stick using the Accutrend analyzer (Hawthorne, NY, USA) (coefficient of variance, 2.8–5.0). These values constituted the “pre-exercise” measurements.
This study used a discontinuous ramped treadmill protocol. Each stage lasted for 3 minutes, with up to a 90-second active rest period (walking at 80.4 m·min−1 at previous stage grade) between stages. Heart rate was recorded 10 seconds before each stage ended through telemetry. The RPE and BLa were measured during active rest. The metabolic measurement system was used to compute V[Combining Dot Above]O2 and RER in 30-second increments. For the first stage, all participants ran at 160 m·min−1 and a 0% grade. For the second stage, all participants ran at 160 m·min−1 and a 5% grade. Each subsequent stage increased by 26.8 m·min−1 and 1% grade until the participant reached volitional exhaustion. For the purpose of this study, LT was defined as the point at which the participant's lactate levels reached 4 mmol or greater (25).
Once the participant reached their volitional physical limit, indicated by them grabbing the handrails, the treadmill was reduced to 80.4 m·min−1 and 0% incline, the mouthpiece and headgear were removed, and they walked for a 5-minute cool down. At 1 and 5 minutes post-exercise, BLa, HR, and RPE were recorded. Seven days later, the participants repeated the maximal test but switched CS condition. All blood samples were taken by the same investigator, in the same manner, for all of the participants, using the same BLa analyzer (2).
Microsoft Excel for Windows 7 and SPSS Version 20 (IBM Corp., Armonk, NY, USA) were used to analyze the data. Mean values and SD (mean ± SD) were calculated for all descriptive measures. Repeated-measures analyses of variance were used to assess the differences in BLa, V[Combining Dot Above]O2, RER, RPE, and HR across testing stage and condition. Paired t-tests were used to analyze the maximum values between the conditions using an alpha level set a priori at p ≤ 0.05. Linear regression analysis was used to analyze the TTF as it related to BLa.
There were no differences in the physiological responses measured in this study under the CS and non-CS conditions other than BLa and recovery TTF. After noticeable differences in BLa between conditions at 1 and 5 minutes post-test were found, paired t-tests were run and showed that BLa was significantly lower while wearing CS when measured during recovery from the treadmill test at 1-minute (CS = 13.3 ± 2.9 mmol·L−1, non-CS = 14.8 ± 2.8 mmol·L−1, p = 0.03) and the 5-minute (CS = 11.0 ± 2.7 mmol·L−1, non-CS = 12.8 ± 2.8 mmol·L−1, p = 0.02) periods (Figures 1 and 2). Paired t-tests revealed that TTF was modestly, but significantly longer without CS (CS = 23.570 ± 2.39 minutes, non-CS = 23.93 ± 2.49 minutes, p = 0.04) (Table 2). To determine whether this had any effect on the recovery BLa levels, a linear r2 analysis was used to determine any significance and was plotted on a line graph. (Figures 3 and 4).
The results indicated that the differences in TTF between the 2 trials accounted for 49% of the variation in BLa for 1-minute recovery data and 63% of the variation in BLa 5-minute recovery data. Therefore, not all of the differences in postexercise BLa levels can be attributed to the CS/non-CS conditions. However, this indicates that the CS were responsible for part of the other 51 and 37%, respectively. Paired sample t-tests showed no significant difference for order effect between the first and second treadmill tests (first = 23.8 ± 2.5 minutes, second = 23.7 ± 2.3 minutes, p = 0.06). Before and during the submaximal stages of the maximal treadmill test, HR, RER, V[Combining Dot Above]O2, RPE, and LT were not significantly different between CS conditions. Peak HR, V[Combining Dot Above]O2max, max RER, and max RPE showed no differences between conditions either (Table 2).
The most important finding of this investigation was the increase in TTF in the non-CS condition. Time to fatigue was significantly longer without CS (CS = 23.570 ± 2.39 minutes, non-CS = 23.93 ± 2.49 minutes, p = 0.04). These findings are in agreement with a previous study that examined the effect of CS on athletes during sprint workout (9). Decreased TTF when wearing CS goes against the manufacturers' claims of the benefits of wearing the CS (24). The decrease in TTF while wearing the CS could hypothetically be explained in several ways. First, this study did not have a protocol for recording anecdotal data. Participants were not asked their opinion of the CS nor could they list any discomfort or feelings, positive or negative, relating to the CS. It is possible that some of the subjects did not like running in the CS. If the subjects had any negative perceptions of the stockings (e.g., too itchy, hot, or restrictive), then this may have affected their performance. Second, the CS may have added weight to the runners, especially as the test went on and sweat made the CS heavier. However, it is unlikely that the weight of the fabric was significantly changing based on the materials that made up the CS.
Order effect could help explain this study's lack of improvement in TTF among the runners in comparison to similar studies. Kemmler et al. (15) observed an increase in TTF with their subjects wearing the CS. Their data illustrated that running performance determined by time under load (36.44 ± 3.49 vs. 35.03 ± 3.55 minutes, effect size [ES], 0.40) and total work (422 ± 78 vs. 399 ± 77 kJ, ES, 0.30) were significantly higher with the CS. However, Kemmler et al. (15) used a different population focusing on recreational runners with a greater age range (25–60 years vs. 18–22 years) and lower mean V[Combining Dot Above]O2max (52.0 vs. 64.1) for their study. Kemmler et al. (15) did not report statistical analysis of testing order. If they did not complete this analysis, it is not unreasonable to hypothesize that some sort of change in performance could have occurred as a result of the order in which the subjects ran their tests. This study accounted for order effect by randomizing the testing. It also found no statistical significance when examining for order effect, but it is unclear whether other studies examined their data post hoc for order effect as well. One would not expect collegiate runners, with a homogenized training level, to perform significantly better/worse on a treadmill test over the course of 1 week.
The CS appeared to have a significant effect on BLa levels after 1- and 5-minute active recoveries, with BLa levels in recovery from exercise being higher for the non-CS conditions (Figures 3 and 4) defined by augmented capacity to remove BLa. This may lend credence to certain manufacturers' claims of improved recovery after exercise (24). There is also the possibility that the lower BLa levels observed in the CS condition were the result of the decrease in TTF displayed by the CS group. Less time spent running would result in decreased BLa levels. This would further suggest that CS decreased performance.
The proposed mechanism behind CS is that they improve oxidation of the muscle through increasing venous return via the calf muscle pump (28). Previous studies have found the use of compression garments of varying length and compression to reduce soreness after bouts of eccentric exercise and other activities (16–18). Specifically, as a study conducted by Kraemer et al. (18) on the effect of commercial hosiery with various levels of graduated compression found that all were effective at attenuating lower leg swelling and venous pooling among normal healthy women. This was followed by a reduction in lower leg discomfort (18). Although this study did not ask participants how they felt after the run between conditions, the previous research does strengthen the idea of CS in recovery from exercise. Kraemer et al. (18) noted that the lower leg swelling was the result of increased creatine kinase (CK) activity in the blood stream after 8 hours of standing, and that CS with even a modest level of compression (15.4 mm Hg ankle, 8.4 mm Hg calf, 8.6 mm Hg thigh) decreased CK activity (18). This study did not measure CK activity between conditions. Also, it is important to note that any benefits from increased muscle pump may not lead to increased BLa buffering in subjects with already highly developed muscle pump function. The effects of endurance training on the body are well established. However, studies examining training effect on calf muscle pump function in healthy populations are lacking.
The available literature focuses on subjects with VI (14,21). Padberg et al. (21) looked at patients suffering from VI and found calf muscle pump function and dynamic calf muscle strength were improved after a 6-month program of structured exercise. Based on these results, it stands to reason that training (running) would result in improved muscle pump function among healthy subjects, and that the runners in this study would have well-developed calf muscle pump function. Aerobically trained improvements in calf muscle pump function might leave little room for improvement because of CS when considering venous return. The results of this study appear to support this contention.
Other than TTF and recovery BLa, there were no differences in the physiological responses measured in this study under the CS and non-CS conditions. There was no difference in BLa levels before or during exercise between CS and non-CS conditions. The CS did not reduce the levels of BLa at each stage between conditions nor did they delay the onset of the LT. Berry et al. (5) did observe decreased BLa levels in the CS trial. They postulated increased retention of lactate in the muscle bed resulted in lower BLa levels from the CS. Although this is physiologically possible, it is untested (5). To further test that hypothesis, more invasive testing of the muscle properties would need to be performed.
A maximal test does not closely resemble a traditional race protocol. Presumably, this may not limit performance if the mechanism that limited maximum TTF does not come into play at race pace. Additional studies could employ a testing protocol that more closely mirrors a typical long distance race, where time is examined as closely as intensity. Further research should also examine whether the level of training will influence the possible effects that CS might have on them. It would be appropriate to examine whether wearing the CS immediately after exercise causes the same decrease in BLa during recovery as in this study. If, in fact, CS decreases TTF, as this study indicates, it needs to be examined whether putting the socks on immediately after exercise would provide the same benefits observed on BLa levels in recovery without negatively affecting the runner's maximal performance.
Previous studies have also monitored their participants for longer periods of time after the exercise bout, and had participants provide information on their perceived level of soreness (9,17,18). Had this study inquired about lower extremity soreness after the 2 treadmill tests, it is possible some better anecdotal recovery data could have been gleaned.
Previous CS research used CS with “slightly degressive” pressure from the ankle of 24 mm Hg (15) and 15–22 mm Hg (27). These pressure ranges are comparable to those in the CS used in this study. Therefore, differences observed in performance and physiological markers are most likely related to other variables, such as participant characteristics/fitness level and test design.
Unfortunately, this study had a non-blind limitation. The subjects were aware when they were wearing the stockings and when they were not. Use of a placebo might have helped eliminate any bias (consciously or subconsciously) that may have existed.
The practical applications of this study appear to demonstrate that CS are not beneficial to highly trained collegiate cross-country runners unaccustomed to wearing CS during a treadmill run to maximal volitional exhaustion. The runners fatigued faster when wearing CS. Accordingly, BLa during recovery was significantly lower due, in part, to the shorter TTF when wearing the CS.
Based on the results of this study, it is unknown whether decreased BLa during recovery benefits physiological recovery from maximal exercise. Therefore, we cannot recommend their use as an ergogenic aid in this population participating in a maximal treadmill test. Accordingly, coaches, trainers, and runners searching for a legal “edge” should exercise caution when using CS during competition. This study demonstrates that although CS did not appear beneficial for a maximal exercise test, they may prove beneficial after exercise. When examining the effects of a purported ergogenic aid, a lack of significant findings is often as critical as significant differences in assessing the validity of the manufacturer's claims. Perhaps, the findings of this study will lead to further examination of the claims made by CS manufacturers to better educate the coaches, trainers, and athletes, both professional and recreational, who use them.
The assistance of Dr. Kevin Darr, Cary Springer (statistical assistance) Jennifer Flynn, and Dr. Scott Conger is gratefully acknowledged. The authors thank Judith Brannan at Sigvaris for donating compression stockings for the study. The authors declare no professional relationship with Sigvaris and state that the results of this study do not constitute an endorsement of the product.
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