Compression garments are widely used in the treatment or prevention of clinical, occupational, and travel-related ailments for their beneficial effect on venous hemodynamics. The extrinsic mechanical pressure they provide to the underlying soft tissues increases cutaneous and subcutaneous interstitial pressure, thereby reducing peripheral blood pooling, leg swelling, and improving venous return (Partsch et al., 2008). Compression garments are also used in healthy populations for post-exercise recovery purposes, although there is no definitive consensus about their effects (MacRae et al., 2011; Born et al., 2013; Hill et al., 2014). Overall, it has been largely demonstrated that compression garments improve perfusion and increase local muscle oxygenation at rest (Bochmann et al., 2005; Bringard et al., 2006), so that many of its expected ergogenic effects are dependent on the subsequent compensation of local oxygen deficit contracted during exercise and fastening of energy stocks reconstitution (Di Prampero et al., 1983).

During the last decade, wearing compression garments during exercise has also become increasingly popular in sports such as running and cycling. Similar to the literature specific to post-exercise recovery, various outcomes have been reported, with no or small beneficial effects in physiological, psychological, or biomechanical parameters (Engel et al., 2016). Wearing compression garments during running exercise was associated with improvements in muscle oxygenation during intermittent high intensity running (Sear et al., 2010), leg volume (Bovenschen et al., 2013), muscle damage using magnetic resonance imaging and histochemical techniques (Valle et al., 2013), delayed onset of muscle soreness (DOMS, see Duffield and Portus, 2007), and heart rate (Varela-Sanz et al., 2011). Positive effects in performance have also been noted in incremental tests (Kemmler et al., 2009; Sear et al., 2010), repeated sprinting (Higgins et al., 2009; Born et al., 2014), and jumping height following submaximal exercise (Rugg and Sternlicht, 2013; Bieuzen et al., 2014) or after a 10 km run (Ali et al., 2011). Conversely, other studies have reported no measurable effect on limb volume (Areces et al., 2015), fractional oxygen utilization (Kemmler et al., 2009; Wahl et al., 2011; Born et al., 2014; Priego Quesada et al., 2015; Stickford et al., 2015), muscle oxygenation or blood flow (Vercruyssen et al., 2012; Born et al., 2014), heart rate or indicators of central cardiovascular adaptations (Ali et al., 2007; Sperlich et al., 2011; Wahl et al., 2011; Vercruyssen et al., 2012; Born et al., 2014; Priego Quesada et al., 2015), lactate or exercise metabolite removal (Kemmler et al., 2009; Ali et al., 2010; Sperlich et al., 2011; Wahl et al., 2011; Vercruyssen et al., 2012; Areces et al., 2015), ratings of perceived exertion (RPE) or DOMS (Ali et al., 2007, 2010; Bovenschen et al., 2013; Areces et al., 2015; Priego Quesada et al., 2015), running economy and gait kinematics (Varela-Sanz et al., 2011; Stickford et al., 2015; Vercruyssen et al., 2016), maximal voluntary and evoked contractions (Vercruyssen et al., 2016), as well as performance in repeated sprinting (Duffield et al., 2008), or in running performed at maximal (Ali et al., 2007; Priego Quesada et al., 2015) and at sub-maximal exercise intensities (Ali et al., 2007, 2011; Wahl et al., 2011; Vercruyssen et al., 2012; Priego Quesada et al., 2015). This abundant but heterogeneous literature may underline probable task-dependent ergogenic effects of the compression when used during exercise.

Recent studies have indicated that the mechanical support provided by compression garments may contribute to reduce the transmission of oscillations or vibrations (Doan et al., 2003; MacRae et al., 2011; Bovenschen et al., 2013), which may in turn reduce fatigue (Miyamoto et al., 2011), and increase performance (Kraemer et al., 1998). Because minimizing musculo-skeletal damage and fatigue is considered paramount for performance in trail running (Millet, 2011), and since prolonged running on trails has been shown to alter footstrike patterns and gait biomechanics (Morin et al., 2011b; Vernillo et al., 2014; Giandolini et al., 2016), it is possible that compression garments have beneficial effects in situations maximizing the exposure to fatigue, shocks and vibrations, such as prolonged running exercise performed on trails with pronounced elevation gain and loss. Despite the increased popularity of trail running over short and long distances, there is only limited evidence available on the effects of compression garments worn during running on trails with uphill and downhill sections (Vercruyssen et al., 2012, 2016; Bieuzen et al., 2014), or for road running for durations longer than ~90 min (Areces et al., 2015). These studies indicate that while compression garments worn during trail running may reduce muscle soreness post-run and the recovery of lower limb power capacity (Bieuzen et al., 2014), there has currently been no evidence of the ergogenic effect of compression garments on the running pace and performance (Vercruyssen et al., 2012; Bieuzen et al., 2014; Vercruyssen et al., 2016). However, all previously cited studies have performed measurements before and after running, and no study on prolonged running >90 min has been designed to measure physiological and biomechanical adaptations of running with compression garments during prolonged trail running.

Therefore, the aim of this study was to determine if wearing calf compression sleeves (CS, compression garments covering the lower limb between the ankle and knee joints) during a prolonged running exercise (~150 min) performed on trails with marked elevation gain and loss, had a measurable effect on local muscle tissue oxygenation, running pattern, muscle power capability, performance, and subjective perception of muscle fatigue, pain and soreness. Because of the various changes in contraction modes and intensities characteristic of trail running with marked elevation gain and loss (changes in gradient, directions, and surfaces), we hypothesized that wearing CS may benefit from improved perfusion and local muscle oxygenation. We also hypothesized that wearing CS would reduce the deleterious effects of fatigue on running biomechanics, muscle power capability and subjective perception, thereby improving performance.

All 14 participants successfully completed the two sessions. There were no significant differences between conditions (CON vs. CS) in standardization parameters weight, ambient and skin temperatures, in the subjective sensations of fatigue or pain prior to running, in the time to complete the small laps, and in the recovery durations between MFT and THT (Table 1).

Baseline measures performed prior to running revealed significant differences between conditions in local mBF (0.12 ± 0.05 vs. 0.17 ± 0.12 mL·min·100 mL⁻¹ in CON and CS, respectively; 95% CI = −0.02, 0.09; p = 0.011; d = 0.54), but not in mV˙O2 (5.08 ± 2.07 vs. 5.35 ± 1.68 mL·min·100 g⁻¹ in CON and CS, respectively; 95% CI = −0.26, 0.80; p = 0.280; d = 0.14). Significant differences were measured in TSI at baseline and after the warm-up for condition (p = 0.035, η²_p = 0.41) and time (p = 0.001, η²_p = 0.72) but not for interaction (p = 0.950, η²_p < 0.001; see Figure 2).

This randomized, cross-over controlled study aimed to measure the effects of wearing calf compression sleeves compared to control garments during prolonged trail running on physiological and biomechanical parameters, exercise performance, and subjective perception of muscle fatigue, pain and soreness. The main findings of this study were that wearing CS compared to CON during trail running (i) improved muscle oxygenation before and after exercise (in a stationary position), but did not differentially affect local muscle oxygenation or heart rate during running on moderately flat or technical and hilly terrain, including during sustained uphill or downhill running, (ii) modified running pattern and muscle mechanical capabilities during hopping via increased leg stiffness, (iii) improved the perception of pain in the Achilles' tendon, and (iv) did not affect performance in all-out trail running with marked elevation gain and loss, which confirms findings of previous studies in shorter duration exercise (Vercruyssen et al., 2012, 2016; Bieuzen et al., 2014).

As expected, HR increased as a function of time (cardiac drift) but we did not find any difference across garment conditions. This result is similar to those of previous studies during (Ali et al., 2007; Duffield and Portus, 2007; Sperlich et al., 2011; Wahl et al., 2011; Vercruyssen et al., 2012; Born et al., 2014; Priego Quesada et al., 2015) or after exercise (Duffield et al., 2010; Ménétrier et al., 2011). On the contrary, a beneficial effect of wearing CS was found in muscle oxygenation during all resting situations, including after the test, which was likely due to an increased perfusion and reduced venous pooling in CS, as previously shown (Bochmann et al., 2005; Bringard et al., 2006; Ménétrier et al., 2011). Changes in skin temperature and skin blood flow have also been pointed to explain part of the improved tissue saturation previously reported with the application of external compression, but these mechanisms are unlikely to play a prominent role in the current study as the control condition we used induced similar calf skin temperature during running compared to CS (cf. Table 1). This result is also in agreement with previous studies having reported improvements in muscle oxygenation before and after running (Bringard et al., 2006; Sear et al., 2010; Ménétrier et al., 2011) and cycling exercises (Scanlan et al., 2008), as we also measured a beneficial effect of wearing CS in all resting situations (muscle oxygenation improved after donning the CS, after warming up, and after the test). However, our study is the first to report findings of muscle oxygenation during prolonged trail running, for which we measured no effect of exercise duration (fatigue) or condition (compression), including during sustained uphill and downhill running. Therefore, it is likely that the pressure in the muscular compartment during running exercises performed on various gradients exceeds the pressure exerted by CS, which could blunt its potential beneficial effects. Previous studies have indicated that increasing the mechanical pressure exerted by compression garments to approximately 40 mmHg had no effects during running at submaximal and maximal intensities in laboratory conditions (Wahl et al., 2011) and could even have detrimental effects on blood flow during cycling exercise (Sperlich et al., 2013). However, by the same mechanism, CS could potentially have ergogenic effects during repeated exercise/recovery phases where the recovery rate in muscle oxygenation is beneficial, such as intermittent exercise (Sear et al., 2010), but also possibly for exercise performed on multiple days. The two sessions were conducted in similar conditions, as no statistical differences were observed in factors that may impact parameters of interest (i.e., ambient and skin temperatures, perceived fatigue and pain before the test, the time separating MFT and THT bouts, and the time to complete the MHT bout).

For the first time, changes in running biomechanics induced by CS were reported during exercise. Beyond the effects of exercise likely imputable to fatigue (large effect sizes for increased step frequency, decreased aerial time, significant increases in vertical stiffness and duty factor), we reported (i) a lower duty factor and greater leg stiffness during the MFT running bout in CS compared to CON (influenced mostly by increases in aerial time), and (ii) greater leg stiffness and vertical stiffness, as well as an interaction effect in duty factor during THT running in CS compared to CON (mostly influenced by decreases in contact time). For lower limb functional mechanical capabilities, while all variables were affected by exercise, we also reported a decrease in contact time and a large tendency for increases in leg stiffness with CS. Previous studies have indicated that the biomechanical adaptations induced by prolonged running were associated with similar trends, such as higher step frequency, smaller ground reaction forces contributing to increased leg and vertical stiffness after a 24-h treadmill run (Morin et al., 2011b), reduced aerial time and increased step frequency contributing to a greater vertical stiffness after a 166-km mountain ultramarathon (Morin et al., 2011a), or higher step frequency, duty factor and lower aerial time and ground reaction force after 8,500 km of running in 161 days (Millet et al., 2009). These biomechanical adaptations were suggested to be related to a smoother and safer running pattern preventing the impact of additional important mechanical constraints on the musculo-skeletal system. In the current study, a higher leg stiffness was also observed with CS compared to CON before, during and after running on level and hilly terrain, and in maximal hopping. However, in contrast with the above-mentioned previous findings associating the increase in leg stiffness with an increase in DF, the higher leg stiffness observed in the current study was associated with lower DF, either via a longer t_a and higher peak vertical force during MFT, or a shorter t_c during HFT and hopping. Therefore, the acute increases in leg stiffness associated with a lower relative time spent in contact with the ground can be interpreted as a more dynamical running pattern and leg mechanical behavior. Previous studies have suggested such biomechanical improvements may reside in the ergogenic aid of compression garments in reducing muscle oscillations (Kraemer et al., 1998; Mizuno et al., 2016), potentially through enhanced proprioceptive capability (Kraemer et al., 1998). However, there is currently no systematic study of the mechanisms underlying these acute changes in leg mechanical behavior wearing CS, and further investigations are required.

In this study, we reported that wearing CS resulted in a lower perception of fatigue in thigh muscles, and for the first time, a lower pain in the Achilles' tendon immediately after exercise. We also observed no effect of compression effect in DOMS up to 7 days after the test, which extends the findings of several other studies (Ali et al., 2011; Bovenschen et al., 2013; Driller and Halson, 2013; Areces et al., 2015; Chan et al., 2016). However, this result differs to that of Bieuzen et al. (2014), where the DOMS measured 1-h and 24-h POST trail running were likely to be lower in the compression condition. The differential alteration in the perceived sensation of fatigue, pain and soreness at the different muscle and tendon sites cannot be elucidated with the current results. Future investigations are needed to precise these discrepancies and may explore the potential beneficial implications of such sleeves, especially when used chronically, since CS could provide analgesic or prophylactic effects by enhancing proprioception and/or reducing the transmission of potentially harmful vibrations (Macefield, 2005). However, despite the improvements in the perception of pain in the Achilles' tendon, and despite the absence of deleterious effects on any other variable, we did not measure improvements in exercise performance in either running (measured using time to complete the large laps) or muscle mechanical capabilities (hopping power). Therefore, it is possible to formulate the hypothesis that (i) the exercise used in the current study may have not been sufficient in duration and/or did not generate sufficient neuromuscular alterations in order for the potential protective action of CS to be transferred in exercise performance (as evaluated from this experimental design), or that (ii) the control garments provided some level of haptic feedback despite the absence of compression, akin to a placebo effect. Finally, the current study was performed in a cohort of trained trail runners and therefore, the potential protective effect of CS during trail running may have been minimized compared to a cohort of participants unfamiliar with running, or unfamiliar with running in terrain with marked elevation gain and loss.

This study shows for the first time that wearing calf compression sleeves during prolonged (~2 h 30 min) trail running modified running biomechanics and lower limb muscle functional capabilities toward a more dynamic behavior, and reduced perception of pain in Achilles' tendon compared to a control condition without compression. In line with previous studies performed in traditional on-road running, or in shorter duration trail running, wearing calf compression sleeves did not modify exercise performance, muscle oxygenation and heart rate. Future studies are required to investigate why the selective improvement of stride biomechanics and Achilles' tendon pain had no effect on exercise performance, using either longer exercise duration or running performed in even more challenging terrain. Wearing compression sleeves during running appears to be associated with no adverse effects on the measured variables.

Conceived and designed the experiment: TR, PS, MaPa, and GM. Performed the experiment: TR, MaPi, and FD. Analyzed the data: HK, TR, PS, and MaPi. Wrote the paper: HK, TR, PS, GM, MaPa, and FD.

This study (REC'UP study) was supported using specific funds and equipment from compression garment manufacturer Thuasne (France).