1. Introduction
Trail running has become increasingly popular in the last decade throughout the world. Trail running is characterized by the succession of long uphill and downhill sections in a natural environment and a large range of distance races (under 5 to above 300 km) can be practiced by recreational or competitive trail runner (Giandolini et al. Citation2016). Factors of performance in trail running vary with the distance of the race and its fields. Performance in ultra-endurance rely on motivational, psychological, physiological, biomechanical and technical factors including equipment (Millet et al. Citation2011). Exercise-induced muscle damage (EIMD) caused by repetitive submaximal running impact seems to be an important limiting factor of performance in ultra-endurance characterized by different types of symptoms including pain, inflammation, and reduced capacity of the affected muscle to produce force post-exercise (Millet et al. Citation2011). Moreover, we know that lower limb muscle natural frequencies are close to impacts induced by running which creates resonance partially attenuated by the pre-impact activation of muscles (Boyer and Nigg Citation2004). Compression garments (CG) are increasingly used in sport and fitness. The initial goal to wear CG was for their thermogenic effect. Then, it has also been observed that CG could cause a prophylactic effect. It was suggested that limiting soft tissue vibration (STV) with the use of CG in running could reduce EIMD induced by the repetition of shocks and thus play a protective effect (Borràs et al. Citation2011). For our knowledge, a limited number of studies have investigated STV induced by impact running with the wore of CG on thigh on different speeds and slope conditions. Thus, the purpose of this investigation was to determine if short thigh CG reduces STV according to different speeds and slope condition.
2. Methods
2.1. Subjects
Twelve healthy males volunteered took part in this study (24 ± 2.5 years; 176.7 ± 5.2 cm and 72.42 ± 5.8 kg, respectively). All subjects were physically active between one to four times per week, none was specifically trained on running. They were fully informed of the study conditions before participating.
2.2. Study design
Each participant had one appointment in the laboratory to perform seven non-randomised running tests conditions twice (8,10,12 km h−1 without slope, 8 km h−1 uphill at 10% and finally 8,10,12 km h−1 downhill with slope at 10% too). Subjects wore (from waist to above knee) either thigh CG (Kalenji©) or a control garment (CON), which consisted of personal loose-fitting conventional running clothing. Each running speed sessions duration was 90 s, with 60 s of familiarisation and 30 s of data collection. Subjects’ thigh circumference was measured then short compression size were chosen based on company guidelines. Participant wore personal shoes usually used on their training session and were familiarised to speed and slope conditions before each session.
2.3. Instrumentation & data collection
Medical treadmill (Medical Developpement©, Varces Allières et Risset, France) was used for the running session. Soft tissue accelerations of vastus lateralis (VL) and impact acceleration with ground on shoe of the right leg were recorded with two triaxial accelerometers (Mega Electronics, Kuopio, Finland, ±50 g & ±100 g, 1000 Hz) on Labchart© software (LabChart7.1, ADInstruments Ltd., New Zealand). VL sensor was placed at one-third of the muscle length from the distal end of the muscle belly. Shoe sensor was located on the counter heel part of the shoe at calcaneum level. Both ‘Y’ axis sensors were aligned with the longitudinal axis of the thigh and shank respectively. Accelerometers were tapped on skin and shoe with double-sided tape then were preloaded with medical stretch adhesive bandage (Hypafix©, BSN Medical) to improve congruence of motion with the soft tissue (VL) and secure probe on the shoe.
2.5. Data treatment
In all, 10 impacts of each speed of CON and COMP conditions were extracted and processed on Matlab© software (Matlab R2018a, MathWorks MA, USA). Temporal domain was explored with the computation of the norm of the three axes. Then, peak accelerations (Accpeak) were identified as the maximal absolute value of the resultant acceleration from the three-acceleration component during each impacts of each condition. Time frequency domain was investigated with a continuous wavelet transform. Mean power signal from 10 to 130 Hz was processed according to Trama et al. (Citation2020).
2.6. Statistical analysis
Descriptive statistic was computed included mean and standard deviation of the 10 impacts for all acceleration variables. Shapiro–Wilk normality test was used to check the normality of samples. A two factors repeated measure (speed x condition) analyse of variance was performed (i.e. garment effect) for downhill and flat conditions speed. A paired sample t-test was used to compare uphill conditions. The significance level was set at p < 0.05.
3. Results and discussion
In the temporal domain, the Accpeak results showed that soft tissue vibrations were influenced by the running speed and CG (). The Accpeak increased significantly with the running speed increment. Moreover, the statistical analysis reported that the Accpeak was significantly lower (−31% in average) when subjects wore CG compared to CON.
Figure 1. Accpeak resultant for different speed and slope conditions. *, †, ¥ indicate a significant difference from CON for a similar speed and slope condition, from 8 km h−1 for a similar slope condition, from 10 km h−1 for a similar slope condition.
For the frequency analysis, mean power signal raised significantly with the increased of running speed (). In addition, the results showed that the CG condition allows to significantly decrease the mean power regardless the speed for each condition of slope (−34% in average). Muscles pre-activation intensities are adapted with the impact magnitude in order to attenuates soft tissue vibrations (Boyer and Nigg Citation2004). We observed higher value of soft tissue peak acceleration for downhill speed and lower value for uphill speed compared to flat running condition. ‘Muscle tuning’ can be accentuated or masked especially on downhill or uphill condition (Ehrström et al. Citation2018). As previously observed, in our study the wore of CG improve the protective effect of ‘muscle tuning’ by limiting STV (Ehrström et al. Citation2018). Moreover, these results regarding the temporal and frequency domain were in accordance with those of Trama et al. (Citation2020) for a running task.
Figure 2. Mean power signal for different speed and slope conditions. *, †, ¥ indicate a significant difference from CON for a similar speed and slope condition, from 8 km h−1 for a similar slope condition, from 10 km h−1 for a similar slope condition.
4. Conclusions
The present study brought new information concerning the influence of the CG on STV according to different speeds and slope condition. Particularly, regarding ergonomics, our findings indicated that CG is adapted at low and high speed but also in the different condition of slope.
Acknowledgements
The authors thank the company DECATHLON® for creating and providing the prototype compressive short.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
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