Original article
Cardio-respiratory and metabolic responses to different levels of compression during submaximal exercise B Sperlich*, M Haegele*, M Kru ¨ger*, T Schiffer†, H-C Holmberg‡§ and J Mester*
*Institute of Training Science and Sport Informatics, German Sport University, Cologne; †Outpatient Clinic for Sports Traumatology and Public Health Consultation, Am Sportpark Mu¨ngersdorf, 50933 Ko¨ln, Germany; ‡Swedish ¨ stersund; §School of Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, O Sports Science, Department of Education, University of Gothenburg, Gothenburg, Sweden
Abstract Objective: The effects of knee-high socks that applied different levels of compression (0, 10, 20, 30 and 40 mmHg) on various cardio-respiratory and metabolic parameters during submaximal running were analysed. Methods: Fifteen well-trained, male endurance athletes (age: 22.2 + 1.3 years; peak oxygen uptake: 57.2 + 4.0 mL/minute/kg) performed a ramp test to determine peak oxygen uptake. Thereafter, all athletes carried out five periods of submaximal running (at approximately 70% of peak oxygen uptake) with and without compression socks that applied the different levels of pressure. Cardiac output and index, stroke volume, arteriovenous difference in oxygen saturation, oxygen uptake, arterial oxygen saturation, heart rate and blood lactate were monitored before and during all of these tests. Results: Cardiac output (P ¼ 0.29) and index (P ¼ 0.27), stroke volume (P ¼ 0.50), arteriovenous difference in oxygen saturation (P ¼ 0.11), oxygen uptake (P ¼ 1.00), arterial oxygen saturation (P ¼ 1.00), heart rate (P ¼ 1.00) and arterial lactate concentration (P ¼ 1.00) were unaffected by compression (effect sizes ¼ 0.00 – 0.65). Conclusion: This first evaluation of the potential effects of increasing levels of compression on cardio-respiratory and metabolic parameters during submaximal exercise revealed no effects whatsoever. Keywords: blood lactate; exercise; oxygen uptake; running; stroke volume
Introduction The popularity of knee-high compression socks in connection with a range of sports, and especially among endurance athletes, has been increasing. Both high-performance and recreational athletes have begun wearing elastic compression socks during a range of activities, in particular endurance events such as running and triathlons.
Correspondence: Dr Billy Sperlich, Institute of Training Science and Sport Informatics, German Sport University Cologne, 50933 Ko¨ln, Germany. Email:
[email protected] Accepted 15 April 2010
Recent studies indicate that compression clothing may enhance endurance performance,1 as well as accelerate recovery after exercise.2 These effects are probably attributable to improved peripheral circulation, including venous return,3,4 more rapid clearance of blood lactate,5 reduced muscle oscillation1,6 and better clearance of markers of muscle damage, such as creatine kinase.2 Although the benefits of compression clothing for diseased, postoperative and/or inactive patients have been described extensively, clear evidence of potential benefits for well-trained athletes is lacking. The contradictory findings concerning the influence of compression socks on performance may be due to differences in test procedures, the degree and area of compression applied, and/or
Phlebology 2011;26:102–106. DOI: 10.1258/phleb.2010.010017
B Sperlich et al. Compression and exercise
failure to adequately assess variables, such as blood flow, during the exercise. In addition, small numbers of subjects, lack of an appropriate control group and the relatively moderate size of the effects obtained also contribute to the varying results. Moreover, pressure from commercial companies who sponsor evaluations of their own products may also introduce bias in some cases. It has been shown that compression stockings reduce venous pooling and improve deeper tissue oxygenation3 through improved venous haemodynamics4 during exercise. Therefore, an elevation of the sock compression from 10 to 40 mmHg might improve cardio-respiratory and metabolic parameters (such as cardiac output and index, stroke volume, arterio-venous difference in oxygen saturation, oxygen uptake, arterial oxygen saturation, heart rate and blood lactate even more). This in turn could favour improved running performance. To date, the effects of increasing compression, especially on cardio-respiratory and metabolic parameters during endurance exercise, have not been evaluated systematically in well-trained athletes. The primary goal of the present study was to address this question applying different levels of compression (0 – 40 mmHg) to well-trained athletes. Our hypothesis was that increasing compression leads to increasing improvement, especially in cardiac output, oxygen uptake, the arterio-venous difference in oxygen saturation and arterial lactate concentration.
Methods Subjects Fifteen healthy, non-smoking, well-trained male runners and triathletes (age: 22.1 + 1.3 years, height: 184.7 + 6.8 cm, body weight: 76.0 + 7.5 kg, peak oxygen uptake: 57.2 + 4.0 mL/minute/kg) volunteered and gave their written informed consent to participate in this study, which was approved by the university’s ethics review board. Prior to the testing, the subjects were fully familiarized with the laboratory exercise procedures. On the test days, they were asked to report to the laboratory well-hydrated, having consumed a light meal at least two hours earlier and not having performed any strenuous exercise during at least the previous 24-hour period.
Test design All of the participants carried out six test protocols on a treadmill (Woodway GmbH, Weil am Rhein
Original article
Germany). On the first test day, they performed a ramp test in order to determine their individual maximal oxygen uptakes and assess the running speed to be employed in the subsequent submaximal tests. The running speed was set initially at 2.8 m/ second, where it was maintained for five minutes, followed by stepwise increments of 0.4 m/second every five minutes until exhaustion was reached. Following this procedure, each participant performed five tests of the same intensity (approximately 70% of peak oxygen uptake) for 45 minutes, but with different levels of compression, applied in a randomized order. For this purpose, all wore compression socks extending from below the knee to the foot from the same supplier (Sigvaris, Winterhur, Switzerland; 94% polyamide and 6% lycra). The mean pressure on the calf at its maximum girth was aimed to be 10, 20, 30 and 40 mmHg, respectively. The level of compression applied to each individual and compression level was prechecked before each test five times at B-level (i.e. at the ankle’s point of minimum girth) and C-level (i.e. at the calf ’s maximum girth) according to international recommendations.7 For this a pneumatic sensor (SIGaTw, Ganzoni, Switzerland) was used to receive the in vivo pressure dimensions at B- and C-level based on a previous study.8 The mean values are presented in Figure 1. All participants were asked not to exercise for at least four days between trials, in order to guarantee adequate recovery. Cardiac output and index, stroke volume, arteriovenous difference in oxygen saturation and oxygen uptake were measured employing a rebreathing unit (Innocor, Innovision, Odense, Denmark) and arterial oxygen saturation sensor (Innovision, Odense, Denmark) as described earlier.9 The closed rebreathing system consisted of a three-way respiratory valve connected to a facemask, an antistatic rubber bag and an infrared photoacoustic gas analyser. Before each rebreathing, an anaesthesia bag was filled with 3 – 6 L of the gas mixture, depending on the individual participant’s predicted vital capacity. To assess cardiac data during exercise, the system calculated the rebreathing parameters for each participant. A maximal bolus volume of 40%, minimal oxygen content of 13% and maximal carbon dioxide content of 15% were employed routinely. Of the 5 – 8 rebreaths taken, the first two or three breaths were excluded from the calculations because of incomplete gas mixing. The unit’s software calculated the pulmonary blood flow and cardiac output from the rate of nitrous oxide uptake. This calculation was based on the slope of a regression line through the plot Phlebology 2011;26:102–106
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Figure 1 Area of pressure measurement (indicated by the dotted lines) as well as the corresponding mean, minimum (Min) and maximum (Max) pressure at B-level (ankle’s point of minimum girth) and C-level (i.e. calf’s maximum girth)
of the logarithmically transformed alveolar nitrous oxide concentrations versus time, while the gas volume of the system was corrected for on the basis of the end-tidal concentration of sulphur hexafluoride. Immediately before and after each test, samples of capillary blood were collected in a capillary tube (Eppendorf AG, Hamburg, Germany) from the right ear lobe for subsequent amperometric-enzymatic determination of lactate [La2] using Ebio Plus (Eppendorf AG, Hamburg, Germany) and of arterial oxygen saturation [SaO2] with AVL OMNI 3 (Roche, Basel, Switzerland). All of these samples were analysed in duplicate and the mean used for statistical analysis.
Statistical analyses The cardiac output and index, stroke volume, arterio-venous difference in oxygen saturation and oxygen uptake of 15 participants were determined on two separate days prior to the study. All of these data were compared with a paired t-test. In addition, the technical error measurement [%TEM] was assessed. The paired t-test indicated no differences between the two days for any of these variables. The %TEMs for cardiac output and index, stroke volume, and arterio-venous difference in oxygen saturation and oxygen uptake were 4.8, 4.8, 4.2, 4.0 and 3.8%, respectively. Under our laboratory conditions, the coefficient of variation for repeated measurements of blood lactate measurements is routinely 1.2% at a concentration of 12 mmol/L. 104
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All data were subjected to conventional calculations and are presented as mean values (mean) + standard deviations (SD). The normal distribution of all sorts of data was also confirmed, so that no further transformation was necessary. Repeated-measures analysis of variance was employed to compare each variable at the five different time points. When an overall difference over time was indicated, Bonferroni post hoc analysis was used to identify where the changes occurred. An alpha value of P , 0.05 was considered to be statistically significant. The effect size Cohen’s d (defined as [difference between the means]/standard deviation [10]) was calculated for all of the variables and the comparison between 0 and 10, 20, 30, 40 mmHg. The thresholds for small, moderate and large effects were defined as 0.20, 0.50 and 0.80, respectively,10 and the highest effect sizes are documented in Table 1. All statistical tests were carried out with the Statistica (version 7.1, StatSoft Inc., Tulsa, OK, USA) software package for Windowsw.
Results All of the values obtained are presented in Table 1. The submaximal cardiac output (P ¼ 0.29 – 1.00), cardiac index (P ¼ 0.27 –1.00) and stroke volume (P ¼ 0.50– 1.00) were similar in the different test situations (effect sizes ¼ 0.00 and 0.52). Moreover, the compression socks had no influence on the arterio-venous difference in oxygen saturation
0.36 0.42 0.36 20.65 20.26 0.00 0.04 20.25 0.14 0.15 0.15 20.30 20.16 0.12 0.01 20.07 0.00 0.00 0.18 20.17 0.04 0.32 0.06 20.03 22.0 + 2.8 11.1 + 1.2 139 + 18.7 63.1 + 6.4 41.7 + 3.6 95.6 + 0.9 159 + 7.0 1.35 + 0.5 Cardiac output (L/minute) Cardiac index (L/kg/m2) Stroke volume (mL) avDO2 (%) Oxygen uptake (mL/minute/kg) Oxygen saturation (%) Heart rate (s/minute) Blood lactate (mmol/L)
20.9 + 2.5 10.5 + 1.1 132 + 16.1 66.2 + 10.9 41.1 + 5.0 95.6 + 0.9 158 + 6.9 1.26 + 0.5
22.0 + 2.7 11.1 + 1.2 139 + 15.4 64.3 + 7.3 41.5 + 5.9 95.3 + 1.0 158 + 7.5 1.37 + 0.7
21.6 + 3.0 10.9 + 1.5 136 + 17.8 65.1 + 7.0 42.3 + 4.1 95.5 + 0.8 159 + 9.6 1.39 + 0.6
21.0 + 2.7 10.6 + 1.2 133 + 15.1 67.7 + 7.6 42.7 + 4.1 95.6 + 0.8 158 + 11.8 1.52 + 0.8
0.29 0.27 0.50 0.75 1.00 1.00 1.00 1.00
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.56 0.57 0.75 0.11 1.00 1.00 1.00 1.00
0.41 0.52 0.39 20.35 0.14 0.00 0.10 0.18
0– 30 0– 20 0– 10 0 Parameter
10
20
30
40
0– 10
0 –20
0 –30
0 – 40
Effect size (Cohen’s d ) P values Compression (mmHg)
Table 1 Responses of different physiological values when wearing different grades of compression socks during submaximal running (70% peak oxygen uptake, n ¼ 15, mean + SD)
0 –40
B Sperlich et al. Compression and exercise
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(P ¼ 0.11 – 1.00), oxygen uptake (P ¼ 1.00), oxygen saturation (P ¼ 1.00) or heart rate (P ¼ 1.00) during submaximal exercise (effect sizes ¼ 20.65 – 0.31). Nor was the lactate concentration in arterial blood affected by the different levels of compression (P ¼ 1.00; effect sizes ¼ 20.25 – 0.18).
Discussion The present assessment of the influence of different levels of compression on cardio-respiratory and metabolic parameters during submaximal exercise revealed, in general, no effects at any level. Since compression appears to enhance blood flow in the venous system, resulting in improved peripheral circulation and venous return,3,4 it was reasonable to expect that increasing compression during exercise might lead to increasing stroke volume and cardiac output. However, increasing pressure on the calves achieved with compression socks had no effect on any of the cardiac parameters examined here. Application of an external pressure of 15 mmHg on an inactive muscle while lying horizontal reduces the cross-sectional area of the superficial and deep venous systems (from 2.65 to 0.53 cm2) and improves mean linear blood flow (from 0.5 to 2.5 cm/s).11 Nevertheless, in a standing position it has been shown that graduated compression does not compress the deep or superficial veins of the calf at rest.12 However, a major mechanism promoting venous return during locomotion (e.g. walking and running) is the ‘muscle pump’ system. Peripheral veins, particularly those in the legs and arms, contain unidirectional valves that promote blood flow away from the limb and towards the heart. Veins located within large muscle groups undergo compression as these muscles contract and, vice versa, become decompressed as the muscles relax. Since our present findings show that increasing compression from 0 to 40 mmHg does not affect any of the cardio-respiratory parameters examined, we conclude that our procedure does not affect venous return in a manner which leads to greater oxygen delivery to the periphery during exercise. Different types of compression clothing also showed no effects on oxygen uptake when compared with a non-compression situation. Bernhardt and Anderson13 have reported that compression shorts have no influence on oxygen uptake in connection with 20-m shuttle runs. In another investigation no effect of military antishock trousers on oxygen uptake during graded arm-cranking exercise was observed.14 In addition, Bringard and Phlebology 2011;26:102–106
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co-workers1 found no effect of compression tights on energy expenditure while running. Although several studies have recorded that compression clothing reduces the blood concentration of lactate following exercise,5,15 no such effect was observed here, where the largest effect sizes (0.18 – 0.25) were moderate at best. Berry and McMurray15 reported reduced lactate concentrations during recovery from a five-minute maximum treadmill test with compression stockings, an observation that was supported later by the findings of Chatard and co-workers.5 However, Berry and McMurray15 found no effect of compression stockings on lactate concentration following a time-to-exhaustion test at 110% maximum oxygen uptake, in agreement with other results involving shuttle-run tests16,17 or a netball-specific circuit.18 Berry and Murray15 state that the lower concentrations detected after their five-minute test were not attributable to shifts in plasma volume, but appeared to be due to an inverse gradient created by the stockings, resulting in lactate being retained in the muscular bed. In addition, our blood gas analyses revealed no differences due to compression. Similarly, Berry and McMurray15 observed no compression-induced differences in pH or oxygen saturation or partial pressure during a bicycle ergometer test at 110% of their maximum oxygen uptake. Furthermore, no effect of full-body compression garments on muscle pH assessed with 31p-MNR spectroscopy was observed during eccentric downhill walking.19
Conclusion Our assessment of the potential effects of compression socks on cardio-respiratory and metabolic values during running at a submaximal level revealed no alteration in cardiac output and index, arterio-venous difference in oxygen saturation, oxygen uptake, absolute oxygen saturation, heart rate or arterial lactate concentration at any pressure level from 0 to 40 mmHg.
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