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This systematic review investigated the effects of wearing below-knee compression stockings (CS) on exercise performance (or sports activity) and associated physiological and perceived indicators. We searched articles on PubMed using the following terms: “graduated compression stockings”; “compression stockings”; “graduated compression socks”; “compression socks” combined with “performance”, “athletes”, “exercise”, “exercise performance”, “fatigue”, “sports” and “recovery”, resulting in 1067 papers. After checking for inclusion criteria (e.g., original studies, healthy subjects, performance analysis), 21 studies were selected and analyzed. We conclude that wearing CS during exercise improved performance in a small number of studies. However, wearing CS could benefit muscle function indicators and perceived muscle soreness during the recovery period. Future research should investigate the chronic effect of CS on Sports Medicine and athletic performance.
The prevention of deep venous thrombosis is one of the first evidence-based benefits of wearing compression sleeve, demonstrated by a clinical experiment in which CS improved the venous return by increasing femoral vein blood flow velocity in hospitalized patients.1 Over time, the interest from the basic medical area has expanded to other fields like Sports Medicine.2 Nowadays, recreational and professional athletes have used CS as a tool for improving performance or accelerate recovery from training or competitions, and also to reduce lower limb volume,3,4 relieve symptoms of muscle soreness, and fatigue.3–6 Such popularity is probably boosted by the possibility to obtain potential ergogenic benefits with a simple and low-cost aid.
There are different types (e.g., shorts for thighs, full-leg) and application modes (e.g., using only after the exercise) for compression garments. However, using CS (bellow-knee) “only during” the exercise are probably more practical (than during recovery, after-exercise) for a significant number of sports/activities. For example, uniform issues would limit whole-body garments in some sports. Also, athletes living in tropical locations could be unmotivated to wear compression garments after training sessions once those garments usually promote higher skin temperatures.7,8 Additionally, there is limited evidence regarding the effects of wearing CS (only) during exercise/training/competition, which could be relevant for Sports Medicine professionals. Therefore, the purpose of this systematic review was to investigate the effect of wearing below-knee CS during exercise (or sports activity) on performance and associated physiological and perceptual indicators.
A systematic literature search was performed by two independent reviewers in PubMed. The following terms: (i) “graduated soccer cotton basketball compression sock”; (ii) “compression stockings”; (iii) “graduated compression socks”; (iv) “compression socks” were combined with “performance”, “athletes”, “exercise”, “exercise performance”, “fatigue”, “sports” and “recovery” (Figure 1).
The studies included in this review met the following inclusion criteria: 1) original studies; 2) comprised samples of adults (≥ 18 yr); 3) participants were healthy; 4) investigated the effects of wearing foot-to-knee (below knee) CS (during exercise) on exercise performance and physiological and perceptual indicators (e.g., muscle fatigue, muscle recovery, musle soreness); 5) trampoline sublimation weed white sock worn during the exercise/test/match; and 6) study protocol included exercise or effort tests and performance analysis.
The literature search occurred between January 01, 1900, until June 30, 2019. We excluded the following type of articles: conference abstracts, case reports, short communications, systematic reviews, meta-analyses, theses, letters to the editor, and protocol papers. Also, we excluded studies involving unhealthy participants: e.g., patients with morbid conditions such as obesity, chronic venous insufficiency, diabetes, hypertension (but not limited to).
The heterogeneity of the selected studies was considerable: e.g., exercise protocols, fitness level of the participants, variables measured. Thus, we have decided not to evaluate the studies chosen from a statistical point of view. Instead, we performed a qualitative analysis, conducted by two authors focusing on the effects reported by the authors and potential practical implications. All other authors read this qualitative analysis carefully, and edits have been incorporated.
Figure 1 shows the search, selection, and inclusion process. The search displayed a total of 1067 papers, which were reduced to 370 after exclusion of duplicate publications. Then, we discarded 39 articles written in non-English languages.9 From the remaining 331 items, we excluded 261 by examining the title. Finally, from the remaining 70 articles, we selected 21 studies for this review according to our inclusion criteria (Figure 1).
Table 1 presents a summary of the studies examining the effects of wearing below-knee CS during exercise on performance and associated indicators. Running was the most common type of exercise in the selected studies (76%, 16 out of the 21 studies), followed by soccer (two studies; 10%), triathlon, calf-rise exercise and cycle ergometer (one study each one; 5%). All studies were performed using a randomized experimental design, with the majority employing a crossover design strategy (13 studies, 62%) (Table 1).
Only two studies found some beneficial effect of CS on performance, and a third study improved subsequent performance (Table 2). Two studies did not find performance effects of CS for the group mean, but the authors highlighted that CS promoted benefits for some individuals. The main effects of CS are presented with compressions between 20 and 30 mmHg. The range between the anti slip wool compression sock values is 12 to 28 mmHg, while the maximum values range from 15 to 33 mmHg.
This systematic review aimed to investigate the effect of wearing below-knee CS during exercise on performance and associated indicators. The main finding is that wearing this kind of CS during exercise (or physical activity) improved performance in a minor part of the studies selected (i.e., 3 out of 21). However, a reasonable number of studies have shown evidence that wearing CS could benefit muscle function or fatigue indicators (e.g., CMJ, specific physical tests) and perceived muscle soreness just after the exercise protocol and/or hours after the exercise bout (e.g., during 1 h, 24 h recovery).
CS and Performance Improvement
One of the main reasons for wearing CS during exercise is probably the expectation of performance enhancement due to potential physiological effects.2 This includes better venous return which hasten metabolic removal from the exercising muscles31 and reduce cardiac load,26 improved proprioceptive feedback and better movement accuracy,32 reduced muscle oscillations, lower muscle damage, inflammation, and soreness.6,31 In the current review, only three studies found some CS-induced benefit on performance but did not present adirect mechanistic explanation. For example, astudy concluded that wearing CS (during two soccer matches, 72 hin-between) resulted in higher distances covered in high-intensity activities which are decisive for soccer. Also, CS promoted alower perceived muscle soreness in thesecond match.17 Although the authors did not measure any direct muscle damage marker, they suggested that CS probably protected the eccentric actions common in soccer matches,33 mechanically (i.e., smaller muscle oscillation).6 In this regard, the oscillating forces experienced by the muscle resulted in reduced muscle fatigue. Thus, the CS might offer a mechanical advantage reducing muscle oscillation and countering fatigue in high-intensity activities (e.g., intermittent acceleration, changing directions).34,35
Another study showed CS-induced ergogenic effects on performance. The authors found an improvement in running performance concomitantly with anaerobic and aerobic thresholds when participants wore CS.18 The benefits of CS-ergogenic effects on performance are attributed to enhanced biomechanical support of the muscles, leading to higher efficiency and lower metabolic costs at given workloads,18,36 reduction of muscular microtrauma,6 and enhanced the proprioception.32 During a 5 km running time-trial (Brophy-Williams et al15) the wearing CS did not affect immediate performance. However, CS generated a positive impact on subsequent 5 km running (i.e., less performance decrement from time-trial 1 to time-trial 2). Again, the underlying mechanism of such benefit is unclear but may be related to increased oxygen delivery, lower muscle oscillation, and better running mechanics.15
Despite the current results, the literature does not indicate robust evidence favoring the use of CS during exercise (i.e., only three studies found benefits on performance). Researchers should be careful in drawing conclusions. Considering that each specific study has (or had) a particular experimental design (e.g., exercise protocol, duration, intensity, variables measured, fitness level of the participants), it becomes difficult to generalize the results from the different studies. Thus, it is essential to consider the risk of bias and heterogeneity of the studies. As the same protocol does not conduct different studies, they will vary in the characteristics of the included population, interventions, diagnostic methods to access outcomes, etc. (clinical heterogeneity). Thus, these studies may be biased.37 Additionally, two studies did not find CS-induced effects on group mean performance, but the authors highlighted the individual improvements: 10 of 19 runners ran the 5 km time-trial approximately 10 s faster,25 and 10 of the 14 runners ran the 10 km time-trial10 approximately 20 s faster. Therefore, individual responses should be carefully evaluated in practical settings.
CS, Muscle Function and Perceived Muscle Soreness
Some studies in the current review have shown that CS can induce lower muscle fatigue after an exercise protocol with the same workload than a control condition.11,14,20,21 The lower after-exercise fatigue may suggest a preserved muscle function. Overall, such studies show the maintenance (based on baseline values) of muscle function by a smaller decrement of performance (or none) in specific muscular tests performed after the exercise protocol (e.g., running time-trial, soccer match). On the same reasoning, the lower perceived muscle soreness found in the current review is also a potential beneficial outcome from CS. The smaller muscle soreness may be particularly relevant for more prolonged periods with multiples exhausting physical activities performed with a short recovery period in-between.17
In one of the studies, competitive runners (VO2max ~69 mL.kg.min) completed four 10 km time-trial wearing control CS (0 mm Hg) and CS with different pressures in a randomized, counterbalanced order.11 The runners performed CMJ tests before and after running as a muscle function indicator. The results showed that CMJ height decreased after control running. However, CMJ performance was improved after running wearing CS (low and medium pressure), suggesting a better maintainance of muscle function. The authors speculated that improvements in proprioception to jump and reduced muscle oscillations due to CS probably collaborated with lower muscle fatigue.11
In other included study, highly trained runners participated in 3 simulated trail races (15.6 km, including uphill and downhill) in a randomized crossover trial.14 Authors measured indicators of muscle function (and also muscle perceived soreness) at baseline, 1, 24, and 48 h after-run. Muscle function decreased after the race, suggesting the appearance of fatigue, which was partially counteracted by CS. More specifically, a beneficial effect from wearing CS was found for isometric peak torque at 1 h and 24 h post-run and for CMJ throughout the 48 h recovery period. Perceived muscle soreness was also lower when runners wore CS during trail running compared with the control condition (1 h and 24 h post-run). Specific muscle contractions during trail running (e.g., eccentric on the downhill portion) might result in more extensive muscle oscillation and soreness. Thus, CS probably reduced the perceived muscle soreness due to the higher preservation of muscle function.14
Miyamoto et al20 showed that CS promoted a smaller extent of reduction (- 6.4 ± 8.5% for CS vs. ?16.5 ± 9.0% for control) of the evoked triplet torque, after a fatiguing protocol (15 sets X 10 repetitions) of calf-raise exercise. The authors suggested that mitigation of muscle fatigue observed in their study could be related to increased venous flow velocity and prevention of the lowering of the intramuscular pH.20
Positive CS-induced benefits on muscle fatigue was also described after a soccer match. Female players of both teams (50% each team, randomly wore CS or control socks) performed tests (agility T, standing heel-rise, and YoYo Intermittent Endurance II) 48 h before (baseline) and immediately after the game. CS resulted in less match-induced fatigue for agility T-test performance (maintenance for CS and decrement in control players) and heel-rise test (both groups had a decrement on the number of repetitions, but higher in control).21
In the current review, some researchers found a beneficial CS-effect on the perceived muscle soreness in lower extremities after the following exercises: high-intensity continuous 10 km road-running,10 15.6 km trail in mountainous terrain,14 in the second match of soccer (72 h between the first game),17 and 24 h post 5 km time-trial.25 Overall, those studies suggested a lower perception of muscle soreness due to less extensive muscle damage (lower muscle oscillation), and better proprioception. However, we cannot rule out a potential placebo effect, once it is hard to control such bias due to the nature of compressive CS versus control socks.
CS, Other Potential Benefits, and Final Considerations
Besides performance, muscle soreness, and muscle function indicators, 15 out of the 21 studies selected in this review presented other variables influenced by CS: lower blood lactate levels,13,22,23 and fibrinolytic activity,29 higher oxygen saturation,19 after the exercise protocol (recovery). Also, lower cardiac stress during exercise has been found.26
Mitigation of exercise-induced muscle damage is a possible effect according to authors that found benefit from wearing CS in this review. However, none of them measured blood markers of muscle damage (e.g., creatine kinase - CK, lactate dehydrogenase - LDH). Curiously, only three studies measured such markers after-exercise: a marathon race,12 a 15.6 km trail-running,14 and half-ironman triathlon competition,16 and found no effect from CS. The lack of measurements of muscle damage markers on several studies herein included may be due to the experimental design and the fact of “only” wearing the CS during the exercise (i.e., more focus on performance than recovery). Longer time-points of measurement after the activity (e.g., time-course of CK for at least 24 h after-exercise) could be necessary to detect a significant change in CK,38 for example.
Finally, we highlight that in a real-world scenario, athletes probably will not use a promising ergogenic aid to improve performance (e.g., CS) only once, as the majority of studies included here. Athletes would perhaps try it in a couple of training session and one competition before to make a final decision. Also, in practical terms, athletes usually may combine different strategies to improve performance and later recovery, such as ischemic preconditioning,39,40 myofascial release, and cold water immersion.41 Currently, the effects of such strategies (isolated or combined) with CS are unknown. Therefore, the interpretation of our findings should have in mind “to see also the forest, not just the leaf”.