Twenty healthy runners were investigated: ten men and ten women; median age 27 (range 22‒35) years; median body weight 71 (51‒88) kg; median height 176 (161‒192) cm; and median body mass index 22 (17‒26) kg/m2. The inclusion criteria were as follows: able to run 10 km in 50‒60 min; good health; age 20‒60 years; and no injury to the lower legs. The subjects were involved in running activities on a regular basis, and the study was approved by the Regional Ethical Review Board. After oral and written information had been given to them, all the subjects signed an informed consent document.
Each subject performed two identical 10-km running sessions on a treadmill (Energetics Power Run 9.0 HRC), one session wearing CS and one session without wearing CS. The order in which the running sessions were performed was decided using a randomized crossover design. Each subject acted as his/her own control. In the running sessions without CS, the subject wore their normal ankle-high socks.
Before the first running session, the circumference of the calf was measured at the widest point of both legs for each subject, to determine the correct size guided by the manufacturer’s instructions (2XU Compression Performance Run Socks, Australia). Every subject received a new unused pair of knee-high CS. According to the manufacturer, the material of the CS was 80% nylon and 20% elastane. The compression is said by the manufacturer to be about 25 mmHg at ankle level when using the size suggested.
Each subject performed a standard warm-up, running with a speed of 8 km/h for 5 min, in the first running session and then decided a running speed between 10 and 12 km/h with no inclination for the 10-km running session. The second running session was performed with the same speed and inclination.
There were 4‒21 days between the two sessions. The variation in days is explained by the availability of the subjects, fitting the sessions in with their work or studies.
Measurements started with the subjects resting in supine position. This was followed by continuous measurements during the 10-km run on the treadmill and finally during a 5-min recovery period with the subjects in supine (resting) position (Fig. 1). The room temperature was between 21 and 23 °C, and the relative humidity was 23–27%.
Blood pressure was measured during the supine and standing resting positions before and after each running session. Blood samples were collected before and directly after the run (within 10 min) in the first session. In the second session, blood samples were collected only after the run.
IMP was measured continuously with a catheter in the test leg of the subject using a micro-capillary infusion system (Hemo 4; Siemens, Erlangen, Germany) and monitor (Siemens SC 9000; Siemens, Gothenburg, Sweden), which have been used previously in studies on the same muscle compartment [17, 18]. The IMP measurements were randomized to the left or right leg before the test, and the same leg was monitored at both sessions for each subject. To minimize the motion artifacts of the IMP measurements, the subjects made a 5- to 15-s stop by jumping aside from the treadmill every 5 min during the running session. When the IMP recordings were made, the subjects went back on the treadmill at the same pace.
Before insertion of a pressure catheter with four side holes at its tip (IMPCATH; ProtomedLabs SAS, Marseille, France) into the anterior tibial muscle, the catheter was connected by a transducer line (200 cm) filled with saline to the pressure recording system and the monitor. Local anesthetic (2 mL of 1% lidocaine) was injected subcutaneously approximately 12 cm below the lateral condyle of the tibia and 2 cm lateral to the tibial tuberosity of the testing leg. Under sterile conditions, a Venflon introducer (1.8 × 45 mm) was inserted through the skin into the muscle in a distal direction, at an angle of 30° from the plane of the skin. The tip of the needle was retracted and the introducer bluntly advanced parallel to the fibers of the muscle, with the foot in a neutral position. Thereafter, the catheter was inserted 5 cm into the plastic sheath. The plastic sheath of the introducer was then removed.
The function of the pressure recording system was controlled by observing the response to externally applied compression of the muscle compartment and active muscle contraction by dorsiflexion of the ankle joint. The pressure recording system was calibrated according to procedures specified by the manufacturer before each measurement. The IMP value was displayed in real time on the monitor. A micro-capillary infusion technique (1.5 mL/h) was used during measurement to create a fluid pathway and establish the catheter patency. The position of the catheter was controlled by ultrasound. The median depth of the IMP catheter insertion was 14.3 (4.4‒18.8) mm in the subjects running with CS and 13.6 (4.4‒22.1) mm when they ran with normal ankle socks.
Muscle Tissue Oxygenation Index (TOI)
The transport of oxygen and its availability in an exercising muscle are basic factors that influence exercise performance . Oxygenation of muscle tissue is directly related to the balance between oxygen consumption and oxygen supply. Near-infrared spectroscopy (NIRS) provides continuous information about the absolute level of muscle oxygenation in an exercising muscle [17, 19]. The NIRS probe unit consists of two detector photodiodes and three laser-emitting diodes held 4 cm apart. The probe was placed and affixed using double-sided adhesive tape centrally over the anterior tibial muscle of the test leg at the same position as the IMP catheter was placed. All NIRS signals were sampled at 2 Hz. Tissue oxygenation of the anterior tibial muscle was quantified using a three-wavelength, continuous-wave NIRS system (Niromonitor NIRO-200; Hamamatsu Photonics, Hamamatsu, Japan). This system simultaneously uses the modified Beer–Lambert and spatially resolved spectroscopy methods to determine concentration changes in oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin, all in real time. The device presents the tissue oxygen saturation in terms of the tissue oxygenation index (TOI), which expresses the ratio between oxygenated hemoglobin and total hemoglobin in the tissue under observation. The TOI value observed at the initial resting period was used as the baseline value. All subsequent data were normalized by dividing their baseline values and multiplying by 100, thus giving an initial value of 100% for normalized data.
Systolic and diastolic blood pressures were measured before and after the run using a pressure manometer (NAIS; Matsushita Electronic Works, Kadoma-shi, Japan), which was applied to the left forearm.
Blood Sampling and Analysis
It is well established that unaccustomed use of strenuous exercise induces muscle damage . Both serum CK and myoglobin reflect muscle membrane disruption and have been used as biological markers to detect such damage [20, 21]. With subjects in supine position before and after the run, blood samples were collected by a nurse and sent to the routine hospital laboratory for analysis. The normal reference values for serum myoglobin are < 90 µg/L. The normal reference intervals for serum CK are 0.6‒3.5 µkat/L in women and 0.6‒6.7 µkat/L in men. Blood samples were collected from each subject before insertion of the IMP catheter and immediately after completion of the experiment (within 10 min). The modular analyzer used was Cobas 8000: module E602 for serum myoglobin and module C502 for serum CK.
The skin and subcutaneous thickness above the anterior tibial muscle fascia and the distance between the fascia and the tip of the IMP catheter were measured using ultrasound with a linear probe (L10-5, Acuson CV70; Siemens Medical Solutions USA Inc., Malvern, PA), with the subjects in supine position and with muscles relaxed .
Paired t test was used to identify statistical differences in two means for IMP and TOI values between the two running sessions (with CS vs without CS). Non-parametric Wilcoxon signed rank test was used to compare matched pairs for serum myoglobin and CK concentrations. For these parameters, the significance level was set at p < 0.05. Statistical analysis was performed with IBM SPSS Statistics 20.