The use of lower-body elastic compression garments such as tights and stockings has gained huge popularity among athletes of all levels. Previous studies have shown that the use of compression garments covering the calf (e.g., long tights and stockings) during exercise improves running economy (7), tissue oxygenation (2), peripheral circulation such as venous return (13), and peripheral muscle fatigue (reduction in forge-generating capacity) (22). However, this effect is not evident when wearing compression short tights, which covers only both thighs (5,19). It is assumed that the reasons for the lack of positive effect in the use of compression short-tights may include inadequate pressure intensity applied by the garments because most sporting compression garments covering the limbs are designed to provide higher pressure distally with gradually decreasing pressure proximally (19,22,24). Thus, in this situation, the pressure intensity may not be sufficient at the midthigh where most muscles have the largest portions of mass. Until now, however, no study has ever examined the effect of the pressure intensity of compression garments at the midthigh on physiological parameters reflecting a metabolic state and/or muscle fatigue.
One approach to monitor the metabolic state of individual muscles of the thigh is the use of magnetic resonance (MR) imaging, which possesses excellent spatial resolution regardless of the depth of the muscle of interest relative to the skin surface. It is well established that muscle contractions result in increases in skeletal muscle proton transverse relaxation times (T2) immediately after the exercise (1,3,8,11,27). Moreover, the T2 value of a muscle is inversely related to intramuscular pH level and positively related to inorganic phosphate (Pi)-to-phosphocreatine ratio of the muscle (8,25). Taken together, it can be assumed that a T2-weighted MR image reflects individual muscle’s metabolic state and the degree of muscle fatigue. Using this technique, we ascertained the effect of different pressure intensities of elastic compression short-tights on the metabolic state of the thigh muscles during running exercise to find the optimal pressure intensity that can hamper muscle fatigue development.
Two experiments were conducted to fulfill the goal of this study. In experiment 1, three wear conditions were tested: two kinds of compression short-tights (approximately 8 mm Hg (LOW) and 15 mm Hg (MID) pressure intensities, respectively) and noncompression short as a control (CON1). In experiment 2, on the basis of the results of experiment 1, the effects of higher pressure intensities were investigated in three wear conditions: compression short-tights with a compression intensity at the thigh of approximately 20 mm Hg (MID-HIGH) and 25 mm Hg (HIGH) and control shorts (CON2). Except for the difference in compression of short-tights and their pressure intensities, the protocols and variables for analyses were the same between experiments 1 and 2 (see succeeding sections).
Eleven healthy young male subjects with no history of orthopedic and neuromuscular disorders participated in experiment 1 (173.3 ± 4.5 cm, 67.3 ± 5.9 kg, 25.6 ± 3.7 yr (mean ± SD)) and experiment 2 (172.4 ± 5.6 cm, 66.8 ± 6.2 kg, 27.0 ± 1.8 yr). Of the 11 subjects in experiment 1, six subjects also participated in experiment 2. Before participation, the subjects were fully informed of the procedures, possible risks, purpose, and their right and gave their written consent to participate. The hypothesis of the present study was not explained to the subjects until termination of the measurements to exclude any potential bias that might affect the results of psychological parameters such as RPE (12). They were requested to continue with their normal dietary practices during the study period, to refrain from strenuous exercising for 24 h before the testing sessions, and to drink as they normally would before a running session to standardize their hydration status. This study was approved by the local ethics committee on human research and performed in accordance with the Declaration of Helsinki.
Subjects participated in three separate sessions in both experiments 1 and 2. In each session, the subjects initially rested in a lying position for 20 min without compression garments. Then, pre-exercise MR-T2 images were obtained from the right thigh (see succeeding section). After the scanning, subjects came out of the scanner and wore one of three testing garments: in experiment 1, a commercially available sporting compression short-tight (C3fit 3F09121; Goldwin, Japan) (LOW), a specially made compression short-tight (MID), and a control garment, which consisted of loose-fitting conventional running short (CON1), whereas in experiment 2, two specially-made compression short-tights (MID-HIGH and HIGH) and control short (CON2). The compression short-tight for each subject was sized according to the manufacturer’s sizing chart. We carefully adjusted the fit of the short-tight and visually and manually confirmed that the fit was proper. Each subject used the same socks, running clothing without compression, and running shoes throughout three sessions in each experiment. They then performed the required running exercise on a treadmill (L7; Landice) set at 0° inclination for 34.5 min including 4.5-min warm-up running, 1.5 min at 6 km·h−1, 1.5 min at 8 km·h−1, 1.5 min at 10 km·h−1, and 30 min at 12 km·h−1 (Fig. 1). The subjects’ RPE using a Borg 6–20 scale was recorded at the initiation, 10th minute, and 20th minute points of 12 km·h−1 of running and immediately before the completion of the running test. Immediately after the completion of the running test, they took off the testing garments and then moved quietly but quickly back into the bore of the MR scanner for the postexercise MR-T2 scanning of the thigh. All running tests were performed next to an MR scan room. Three sessions were interspersed by more than 6 d to allow sufficient rest and performed at the same time of the day to minimize any influence of circadian rhythm.
Subjects lay supine with their legs relaxed and knee joint at 180° on a 1.5-T MR scanner (Signa Excite 1.5T; GE Healthcare). The T2-weighted MR images of the right thigh were recorded from the 50% level of the thigh length between the greater trochanter and the lateral condyle of the femur for each subject using an 8-channel body array coil (echo times: 25, 50, 75, and 100 ms; repetition time: 2000 ms; matrix: 256 × 256; field of view: 240 mm; slice thickness: 10 mm; gap: 20 mm) before and immediately after each running test (Fig. 2). Ink marks on the skin of the thigh aligned with cross hairs of the scanner allowed similar positioning for the repeated scans. The time that elapsed from the completion of the running to the initiation of the scanning was 69 ± 5 s and 70 ± 5 s in experiments 1 and 2, respectively, which were comparable with those in previous studies (14,26). The times A representative T2 value of each muscle of the knee extensors (vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris), hamstring (long head of the biceps femoris, semitendinosus, and semimembranosus), and hip adductors (adductor magnus, adductor longus, and gracilis) was calculated using a software (ImageJ; National Institutes of Health). Care was taken to exclude noncontractile tissues such as intramuscular fat, aponeurosis, and blood vessels from the analysis. The same person performed all analyses.
On another day, the pressure exerted on the right thigh by the compression short-tights was measured at five sites of the 50% level of the thigh length for each subject. The five sites were above the muscle bellies of the vastus lateralis, rectus femoris, gracilis, semimembranosus, and biceps femoris muscles. During the measurement, each subject stood on a wooden box only with the left leg and relaxed his right leg away from the ground contact because muscle contractions for standing can affect the pressure intensity. The pressure sensors of a contact pressure monitor (AMI3037-2B; AMI Techno, Japan) were inserted from the top of the compression short-tights. This measure was performed once for each subject. The average pressure intensity at each site was calculated for a 1-s period with a steady output.
For the parameters of RPE and T2, separate two-way ANOVA (time–wear) with repeated measures were performed. When a significant interaction was observed, additional one-way ANOVA with Dunnett, Tukey, and paired t-tests were performed to determine whether significant differences existed between pre- and postexercise and between conditions. For the data of pressure intensity, a two-way ANOVA (site–wear) with repeated measures was used. When a significant interaction was observed, additional one-way ANOVA with Tukey and paired t-tests were performed. The significance level for all comparisons was set at P ≤ 0.05. The statistical analyses were performed by a statistical software (SPSS Statistics 20; IBM Japan, Japan). All data are expressed as mean and SD.
Table 1 shows the contact pressure intensities of compression short-tights at five sites. Two-way ANOVA revealed a significant site–wear interaction (P < 0.05). Follow-up analyses demonstrated that, in LOW, the pressures at the vastus lateralis and rectus femoris sites were significantly smaller than those at the gracilis, semimembranosus, and biceps femoris sites (P < 0.05), whereas no significant difference was observed among the sites in MID.
According to two-way ANOVA, a significant interaction was found in experiment 1. Further analyses revealed that RPE was significantly higher in CON1 compared with that in MID at the 20-min point and in LOW and MID immediately before the completion of the running exercise (P < 0.05) (Fig. 3).
Figure 4 shows the T2 of each muscle before and after the running exercise. For the quadriceps femoris, there was no significant main effect and interaction in the vastus medialis and rectus femoris (Fig. 4, upper panels). In the vastus lateralis, there was a significant interaction. Further analyses demonstrated that a significant increase in T2 after the running was observed only in CON1 and that after the running, T2 was significantly smaller in MID than that in CON1. Regarding the vastus intermedius, a significant interaction was found and there was a significant difference in T2 between before and after the running in CON1 and LOW but not in MID.
For the hamstring, there was a significant time–wear interaction in the biceps femoris and semimembranosus. In the biceps femoris, although T2 was significantly increased after the running in all conditions, T2 elevation was significantly smaller in CON1 than that in MID. For the semimembranosus, a significant increase in T2 was found only in CON1 and there was a significant difference in T2 after the running between CON1 and MID. Regarding the semitendinosus, two-way ANOVA demonstrated a significant main effect of time with no interaction (Fig. 4, middle panels).
Regarding T2 of the hip adductors, two-way ANOVA revealed significant interactions for the adductor magnus and longus but not for the gracilis. Follow-up analyses showed that, in the adductor magnus, a significant T2 elevation was observed only in CON1 and that, after the running, T2 was significantly greater in CON1 than that in LOW and MID. For the adductor longus, although T2 was significantly increased in all conditions, T2 elevation was significantly smaller in MID than that in CON1 after the running. For the gracilis, a significant main effect of time with no interaction was found (Fig. 4, lower panels).
Two-way ANOVA showed significant main effects of site and wear (P < 0.05), with no significant site–wear interaction. Follow-up analyses demonstrated that the pressures at the vastus lateralis and rectus femoris were significantly smaller than those at the gracilis and semimembranosus sites (P < 0.05) (Table 1).
Two-way ANOVA demonstrated that there was a significant main effect of only time (P < 0.05), without a significant interaction of time–wear (Fig. 3).
Figure 5 demonstrates the T2 of each muscle before and after the running exercise in experiment 2. For the quadriceps femoris, there was no significant main effect and interaction in the vastus medialis and rectus femoris, whereas a significant main effect of time without a significant time–wear interaction was found (Fig. 5, upper panels).
For the hamstring, there was a significant time–wear interaction in the biceps femoris and semitendinosus (P < 0.05). In the biceps femoris, although T2 was significantly increased after the running in all conditions (P < 0.05), T2 elevation was significantly smaller in MID-HIGH than that in HIGH condition after the running (P < 0.05). For the semitendinosus, T2 was significantly smaller in MID-HIGH than that in CON2 and HIGH after the running (P < 0.05). For the semitendinosus, two-way ANOVA revealed a significant main effect of time with no interaction (P < 0.05) (Fig. 5, middle panels).
Regarding T2 of the hip adductors, two-way ANOVA revealed a significant main effect of time with no time–wear interaction in the adductor magnus and gracilis. For the adductor longus, there was a significant time–wear interaction (P < 0.05). Further analyses demonstrated that although T2 was significantly increased in all conditions, T2 was significantly smaller in MID-HIGH than that in CON2 and HIGH after the running (P < 0.05) (Fig. 5, lower panels).
The main findings of this study were 1) T2 were significantly increased after a 30-min treadmill running at 12 km·h−1 in all conditions in the hamstring and hip adductors, 2) after the running, T2 was significantly smaller in MID (approximately 15 mm Hg) than that in CON1 for the biceps femoris, semimembranosus, adductor longus, and adductor magnus muscles, 3) after the running, T2 was significantly smaller in MID-HIGH (approximately 20 mm Hg) than that in CON2 and HIGH for the biceps femoris, semimembranosus, and adductor longus. Although the physiological mechanism(s) for the exercise-induced T2 increase in the MR image has not been fully understood, it is well established that muscle contractions result in increases in T2 immediately after the exercise (1,3,8,11,27). This exercise-induced increase in T2 is sensitive to as few as two muscle contractions (29). Moreover, patients experiencing the McArdle disease (i.e., glycolytic and glycogenolytic disorders due to myophosphorylase deficiency) do not show an elevation in T2. Furthermore, the T2 value of a muscle is inversely related to intramuscular pH level and positively to Pi-to-phosphocreatine ratio of the muscle (8,25). Reduction of intramuscular pH and/or accumulation of cytoplasmic Pi have been shown to impair muscle contractile properties such as maximal isometric force and shortening velocity (9,23,28). Thus, the present results strongly suggest that wearing an elastic compression short-tight with a pressure intensity of 15–20 mm Hg can reduce development of fatigue of exercising muscles during submaximal running exercise.
The effectiveness of compression garments has been a topic of great interest over several years, although it remains unclear whether wearing compression garments can have positive effects on some physiological parameters during submaximal running exercise. Information about the pressure intensity is essential to compare findings across studies. However, pressure intensities of compression garments are too often unreported in previous studies on compression garments. Among only a limited number of studies, which reported the pressure intensity, Bringard et al. (6,7) have shown a lower aerobic energy cost during running when wearing a compression long-tight (approximately 20 mm Hg at the calf) compared with that when wearing a conventional noncompression running garment. In contrast, Goh et al. (12) have failed to find a positive effect of wearing a compression long-tight (13.6 and 8.6 mm Hg at the calf and thigh, respectively) on oxygen consumption during running. In addition, a study with compression stockings reported that wearing compression stockings with high pressure intensity (21–25 mm Hg at the calf) could reduce development of the peripheral muscle fatigue of the triceps surae induced by repetitive calf raise exercise, whereas control (7–8 mm Hg) and compression stockings with low pressure intensity (12–14 mm Hg at the calf) did not (22). Taken together, whether a compression garment, which covers the calf, has positive physiological effects may depend on its pressure intensity. This notion was confirmed for the thigh, especially the hamstring and hip adductors, by the present study. In our experiment, however, the pressure intensity by a garment was not uniform among sites at the same thigh length level. The nonuniformity of contact pressure might be attributed to the differences in muscle and/or percutaneous adipose thickness. Thus, it may be difficult to apply the optimal pressure intensity of a segment to other segments.
One of the possible mechanisms for the reduced muscle fatigue during a 30-min submaximal running exercise by wearing compression short-tights with an adequate pressure intensity (i.e., approximately 15–20 mm Hg) in the present study is the removal of metabolites such as H+ and Pi from the exercising muscles because of improvement of the peripheral circulation (13,20). As mentioned previously, reduced intramuscular pH and/or accumulated Pi impair the muscle contractile properties such as maximal isometric force and shortening velocity (10,23,28). Unfortunately, until now, although there seems to be no study supporting the premise that compression short-tights covering only both of the thighs could improve peripheral circulation, it is likely that compression short-tights with an adequate pressure intensity assist muscle pump for reducing venous stasis and facilitating venous return, consequently reducing muscle fatigue (our unpublished data).
Another possible mechanism is a reduction in muscle oscillation during submaximal running exercise. Kraemer et al. (16) reported that power outputs during repetitive maximal vertical jumps were increased and muscle oscillation at the thigh was decreased when wearing compression short-tights (not available about the pressure intensity). Similarly, Doan et al. (10) have shown that wearing compression short-tights (not available about the pressure intensity) enhanced maximal vertical jump height and reduced muscle oscillation of the thigh during vertical jump landing. Furthermore, it has been recently shown that the electrically induced tetanic torque of the quadriceps femoris was significantly enhanced when the thigh was compressed at 20 mm Hg compared with that when compressed at lower or higher pressure intensities (21). These findings suggest that muscular performance can be enhanced by wearing a compression garment with a proper pressure intensity at the thigh. It is possible that this is true for continuous running, which requires propulsive power production at a short contact time. In addition, as Kraemer et al. mentioned (18), the underlying mechanisms by which compression garments mediate any beneficial effects should be carefully considered to understand if the garment characteristics match the needs of the individual. Thus, further studies are needed to reveal the precise mechanisms for the reduced muscle fatigue by wearing the compression short-tight used in the present study.
Because compression garments apply pressure to the body, it is difficult to design an experiment to blind experimental conditions. Previous knowledge of the assumed benefit of compression garments has been suggested to predispose subjects to believe that the use of a compression garment could improve their performance (12). It has been reported that 93% of subjects believed that compression garments were supportive for their physical performance (4). Thus, even CON1 and CON2 in the present study (i.e., the use of a loose-fitting garment without compression) might not serve as a control from the viewpoint of psychological effect. Moreover, compression intensity and construction of garments can create the potential for optimal skin contact, which is vital for proprioception (kinesthetic sense), which mediates many of the garments’ performance effects (15–18). In the present study, however, we confirmed that garment movement, which can affect kinesthetic sense (18), was minimal and the garment stayed in contact with the skin after the running exercise in all conditions, although RPE was smaller only in both LOW and MID than that in CON1 of experiment 1, whereas a significant difference in T2 after the running exercise was observed between CON1 and MID but not between CON1 and LOW. Thus, perceptual and psychological effect does not necessarily appear in physiological aspect.
In conclusion, this study revealed that the running exercise-induced increases in T2, which reflect the intramuscular pH and Pi level of the muscle, were significantly smaller in the biceps femoris, semimembranosus, adductor longus, and adductor magnus muscles when wearing compression short-tights with a compression intensity at the thigh of 15 mm Hg compared with that when wearing a short-tight with compression intensity of 8 mm Hg, whereas T2 after the running exercise with compression short-tights with 20 mm Hg was significantly smaller than that with compression short-tights with 25 mm Hg. The findings suggest that wearing compression short-tights with a pressure intensity of 15–20 mm Hg at the thigh can reduce development of fatigue of exercising muscles during submaximal running exercise in healthy adult males.
The authors would like to acknowledge Toray Opelontex Co., Ltd., for specially making the compression short-tight for this study. No funding was received for this work.
The authors report no conflict of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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