[ad_1]
Approach to the problem
The overall goal of this study was to compare the acute physiological effects after a single session of muscle damaging exercise, carried out under HYP and CON in healthy females, and to compare the effects on subjective and objective recovery characteristics during a 72-hrs period.
The muscle damaging exercise protocol comprised a plyometric task, where all participants conducted 5 × 20 drop-jumps with a 2-min break between the sets. The participants conducted this task either under hypoxia (FiO2: 12%) or normoxia (FiO2: 21%).
To investigate the acute physiological responses, capillary oxygenation, muscle oxygenation of the m. quadriceps femoris, heart rate, core- and skin temperature were assessed directly after each exercise set.
To observe the effects between exercising in hypoxia and normoxia on recovery characteristics, subjective (delayed onset of muscle soreness), and objective (pro-inflammatory cytokines, muscle swelling of the m. quadriceps femoris, countermovement-jump, and maximum voluntary isometric contraction of the knee extensors) parameters were assessed. These recovery characteristics were assessed at 24 h, 48 and 72 h after the muscle damaging exercise task.
Participants
Female participants were eligible for the study, if they were healthy, between the age of 18 to 35 years, recreationally active (non-competitive physical endurance training, 2 to 3 times per week, 30 to 60 min per session) without previous injuries and surgeries. Participants were excluded from the study if they were smokers, pregnant, had acute injuries or painful situations, were exposed to altitude over 1000 m (including commercial flights) for at least one month, or were taking medication. They were instructed to maintain their normal daily habits, but 72 h before the experimental trial, participants were instructed to avoid strenuous exercise, alcohol, energy drinks, or other substances that could affect their physiological performance.
The participants were assigned either to the HYP group or the CON group using block randomisation by drawing lots. Two researchers (RC, EH) were responsible for the enrolment of participants, and screening the written inclusion and exclusion criteria from the questionnaire. One researcher (EH) was responsible for the random allocation sequence and assigning participants to the groups. Written informed consent was obtained from all study participants included in the study. Data collection took place between February 2022 and May 2022 in the laboratory (RESlab, University of Applied Sciences and Arts of Southern Switzerland, Landquart, Switzerland).
This study was approved by the local Ethical Committee of Zurich (2021 − 00546). The study is registered in the clinicaltrials.gov registry (NCT04902924; 26/05/2021) https://clinicaltrials.gov/ct2/show/NCT04902924. The CONSORT guidelines 2010 on reporting randomized trials were followed [31]. The S1 CONSORT 2010 flowchart and S2 CONSORT 2010 checklist can be found in the supplementary materials.
Study design
This randomised controlled study was carried out over five experimental days using a parallel group design.
On day 1, participants filled out a screening questionnaire for eligibility (inclusion and exclusion criteria) and were familiarised with the experimental set-up (countermovement-jump on the jump mat and maximum voluntary isometric contraction on the ergometer chair).
On experimental day 2 (1 week after day 1), the anthropometric measurements were conducted, and the menstrual cycle data (using the calendar method) were recorded, to ensure that the hormonal levels in both groups are comparable. Then all baseline measurements were performed before assigning the participants randomly either to the HYP group or the CON group (block randomisation). After randomisation, the participants performed the muscle damaging exercise protocol, to induce moderate muscle damage (explained later). To evaluate the different physiological responses and the effects on muscle recovery between the conditions, the HYP group performed the exercise protocol at a PiO2 of 80 mmHg, while the CON group performed the same exercise task at a PiO2 of 140 mmHg.
The physiological parameters, capillary oxygenation (SpO2), muscle oxygenation (SmO2), heart rate, core temperature (Tcore) and skin temperature (Tskin) were measured at baseline, and immediately after each set (in total 5 sets) of the exercise protocol (ES1 to ES5), with the participant always in a standing position. Additionally, ratings of perceived exertion (RPE) and dyspnea (DYS) were also recorded at the end of each set of the protocol (ES1 to ES5).
Markers of muscle recovery were assessed at baseline (day 2), 24- (day 3), 48- (day 4) and 72-hrs (day 5) after the muscle damaging exercise task, always in the following order: venous blood collection, anterior thigh muscle swelling, ratings of delayed onset of muscle soreness (DOMS), two-leg countermovement-jump (CMJ) performance and single-leg maximum voluntary isometric contraction (MVIC) of the right knee extensor muscles. A schematic representation of the test protocol is presented in Fig. 1.
Schematic illustration of the experimental design
Muscle-damaging exercise protocol
A muscle damaging exercise protocol was chosen to induce muscle damage on the knee extensor muscles and comprised five sets (ES1 to ES5) of 20 drop-jumps from a 0.6 m box, as conducted previously [18]. According to the literature, this exercise task can be considered to induce moderate damage to the knee extensor muscles [32,33,34]. The participants had a 2-min break between each set, where the physiological parameters were assessed. The participants were allowed to sit down and rest after the parameters were collected. They were not allowed to drink water because of the potential influence of the ingested water on the Tcore data. The participants were verbally encouraged and instructed, if necessary (during the muscle-damaging exercise), to flex their knees at least 90° after the landing and to maintain their arms akimbo during the entire drop-jump.
Hypoxic and normoxic environment
The participants performed the muscle damaging exercise task either under HYP or in the CON environment in the laboratory. In the HYP group, a custom-made (Mile High Training, Franklin NY, USA) tent (3.0 × 3.0 × 2.4 m) was used to create the normobaric hypoxic environment (FiO2: 12% [altitude of 4400 m], PB: 712 mmHg, PiO2: 80 mmHg). The tent was inflatable and an altitude generator (Everest summit II, Hypoxico, Bickenbach, Germany) was used to create an FiO2 of 12%. The hypoxic environment was controlled using an oxygen analyser (OxiQuant S, Envitec, Wismar, Germany). The participants entered the hypoxic tent and started the muscle-damaging exercise after breathing the hypoxic air for 2 min. During CON, the participants performed the same exercise protocol in the laboratory room (7.0 × 14.0 × 2.5 m) at a FiO2 of 21%, PB of 712 mmHg and a PiO2 of 140 mmHg, respectively.
Physiological parameters during muscle damaging exercise
Capillary oxygen saturation
SpO2 from the left index finger was assessed using a pulse oximeter (Nonin 7500, Nonin medical b.v., Amsterdam, Netherlands). Pulse oximetry has been demonstrated to be a valid measurement tool until a desaturation value of 85% is reached in a hypoxic environment [35]. The values from the pulse oximeter (in %) were displayed and transmitted to a computer.
Muscle oxygen saturation
SmO2 was measured with the deep tissue oxygen monitor (moorVMS-NIRS, moor instruments, Millwey, UK), using probes that are placed on the skin [33, 36]. Each probe consists of a detector head that contains two identical photodiodes and an emitter head with two near-infrared LEDs, emitting light at approximately 750 and 850 nm. A standardised probe separation holder of 30 mm was used for reliability reasons. The probes were taped (Hypafix, BSN, Hamburg, Germany) on the muscle belly of the vastus lateralis of the right quadriceps femoris muscle, as previously described [36]. Oxygenated (OxyHb), deoxygenated (DeOxyHb) and total haemoglobin (TotHb) were collected in absolute values and expressed in arbitrary units. SmO2 was calculated (OxyHb / TotHb x 100) and expressed as a percentage value. The indirect assessment of muscle metabolism using near-infrared spectroscopy technology has been demonstrated to be a valid and reliable assessment tool [37].
Heart rate
Heart rate was recorded using a polar watch (Polar, V800, Kempele, Finland) and a Bluetooth chest belt (Polar, H10, Kempele, Finland). The Polar V800 monitor has been demonstrated to be an accurate tool for the measurement of heart rate during exercise [38]. Heart rate values were analysed using absolute beats per minute (b•min− 1).
Core temperature
Tcore was recorded using the e-Celsius ingestible capsules and the e-Viewer (Body Cap, Caen, France). The capsule was ingested from the participants when entering the laboratory (day 2) with the instruction to swallow it immediately. Data were recorded every 30 s, stored within the capsule and transmitted to a computer at the end of the experiment before the participants left the laboratory. The ingestible temperature sensor has been demonstrated to represent a valid index of Tcore and to underestimate rectal temperature by 0.2 °C during exercise [39, 40]. Absolute values (°C) were used for the analyses.
Local skin temperature
Superficial Tskin of the anterior thigh was assessed using the conductive iButton (DS1922L) system (Maxim Integrated, San Jose, USA). The temperature logger was taped (K-active Tape Classic, Europe GmBh, Hoesbach, Germany) on the right anterior thigh, 2 cm above the probes for assessing SmO2. It has been demonstrated that the iButton system is a valid and reliable instrument for measuring skin temperature in humans [41]. Absolute values (°C) were used for the analyses.
Subjective parameters during muscle damaging exercise
Ratings of perceived exertion
The participant’s RPE were assessed using a vertical BORG scale, ranging from 6 “no exertion” to 20 “maximum exertion” [42], which were used for the analyses. Before the experimental procedure, the participants were familiarized with the RPEs scale. At baseline and the end of each exercise set, the participants were asked to rate their physical exertion level by telling one number.
Ratings of dyspnea
Acute DYS was assessed using the modified BORG scale for dyspnea, ranging from 0 “no dyspnea” to 10 “maximum dyspnea” [43]. The modified BORG scale for dyspnea has been demonstrated to be an instrument for clinical practice to measure dyspnea at exercise, with a moderate specificity [44]. Dyspnea status was assessed at baseline and the end of each exercise set.
Recovery parameters after muscle damaging exercise
Venous blood sample
A venepuncture from the antecubital fossa was performed to collect blood from the participants. For the blood sedimentation rate (BSR), a venous blood sample was collected in 5.0 ml EDTA tubes (BD Seditainer, Plymouth, UK). Samples were placed into the sedimentation measurement stand (BD Seditainer, Plymouth, UK). After the sample rested for one hour in a vertical position, the BSR was reported in mm/hr, according to the Westergren method [45]. For the assessment of CRP and CK, an additional venous blood sample was collected in 8.5 ml tubes (BD Vacutainer, Plymouth, UK), centrifuged (3000 g for 10 min; Hettich, EBA 20, Baech, Switzerland) and analysed using the turbidimetric method (CRP) [46] and using an automated ultraviolet method (Roche, Basel, Switzerland). The venous blood samples were analysed using normalised values to baseline.
Muscle swelling
Muscle swelling of the right quadriceps femoris muscle was evaluated using an ultrasound system (MyLabClass C, Esaote, Genoa, Italy) in B-mode. By using the minimal pressure technique, the distance between the femoral bone and the outer layer of the quadriceps muscle (excluding the overlying adipose tissue) was used to evaluate muscle swelling. For reliable measurements over the experimental days, the measurement position for the ultrasound probe was marked, at 60% of the distance between the greater trochanter and the lateral epicondyle, 3 cm lateral to the midline [18, 33]. Normalised values to baseline were used for the analyses.
Delayed onset of muscle soreness
Subjective anterior thigh soreness was rated using a horizontal VAS, ranging from 0 to 100 mm [47]. Participants were instructed to rate their DOMS status during a 3-second lasting 90° squatted position. The far left of the scale (0 mm) indicated no soreness at all, and the far right of the scale (100 mm) indicated severe muscle soreness. Absolute values (mm) were used for the analyses)
Countermovement jump
The maximum CMJ performance was assessed on a jump mat (Just jump, Probotics Inc, Huntsville, USA). The participants were instructed to stand on the mat, place their hands on their hips, and perform a maximum CMJ [47]. A total of three attempts were performed in a row and the highest values were used for the analyses. The participants were not verbally encouraged and remained blinded to the CMJ values throughout the experiment. Values were normalised to baseline for the analyses.
Maximum voluntary isometric contraction
The MVIC (measured in kg) of the right knee extensor muscles was assessed in a seated position on an ergometer chair (EROS-1, Landquart, Switzerland). The participant’s right leg was positioned with a knee angle of 120° and a hip angle of 100°, to obtain reliable results [33]. After positioning, the participants were instructed to perform a maximum isometric contraction for the duration of three seconds, without verbal encouragement. A total of three sets were performed with a one-minute break in between and the maximum value was taken for the analyses. The participants were blinded to the MVIC values throughout the experiment. MVIC values were normalised to baseline for the analyses.
Sample size
Using data from a study employing a similar methodological design [18] the sample size was determined using G*Power (version 3.1.9.3) [48]. The following design specifications were considered: α = 0.05; 1-β = 0.8; f = 0.4; statistical test = Repeated Measures ANOVA with within-between interaction. The total sample size estimated according to these specifications was n = 12 participants.
Statistical analyses
The statistical analyses were performed using SPSS statistics V. 28 (IBM Corp., Armonk, USA), with the significance level set at p < 0.05. Descriptive results are reported as means ± standard deviations (SD). The assumption of normality was assessed using the Shapiro-Wilk test. Mixed design repeated measures ANOVAs were used to assess the main effects of time (physiology and subjective variables: baseline, after exercise set 1, set 2, set 3, set 4, and set 5; recovery variables: baseline, 24-hrs, 48-hrs, 72-hrs) as within factor, condition (HYP, CON) as between factor, and to assess interaction effects (time*condition). Post-hoc analyses were performed using Tukey’s HSD test where appropriate. The effect sizes were expressed as partial eta-squared (η2partial) with values of 0.1 to 0.29, 0.30 to 0.49, and > 0.5 considered as small, medium, and large, respectively [49].
[ad_2]
Source link
