Applied Physiology

Effect of external compression on femoral retrograde shear and microvascular oxygenation in exercise trained and recreationally active young men Abstract Introduction Retrograde shear causes endothelial damage and is pro-atherogenic. The purpose of our study was to examine the impact of vascular remodeling from habitual exercise training on acute changes in retrograde shear and microvascular oxygenation (SMO2) induced via 30 min of external compression. Methods Participants included 11 exercise trained (ET) men (Division I track athletes; age 20 ± 3 years) and 18 recreationally active (RA) men (age 23 ± 5 years). Near-infrared spectroscopy (NIRS) was used to measure vastus medialis SMO2. Doppler-ultrasound was used to assess SFA intima-media thickness, diameter and flow velocity to derive retrograde shear. Vascular measures were made at baseline (BASELINE), during a sham condition (calf compression to 5 mmHg, SHAM) and during the experimental condition (calf compression to 60 mmHg, EXP). Results Compared to RA, ET had larger SFA diameters (0.66 ± 0.06 vs 0.58 ± 0.06 cm, p < 0.05) and lower SFA IMT (0.33 ± 0.03 vs 0.36 ± 0.07 mm, p < 0.05). Retrograde shear increased similarly in both groups during EXP (p < 0.05) but ET men had lower overall retrograde shear during the conditions (BASELINE 75.8 ± 26.8 vs EXP 88.2 ± 16.9 s−1) compared to RA men (BASELINE 84.4 ± 23.3 vs EXP 106.4 ± 19.6 s−1p < 0.05). There was a similar increase in SMO2 from BASELINE to SHAM (ET + 8.1 ± 4.8 vs RA + 6.4 ± 9.7%) and BASELINE to EXP (ET + 8.7 ± 6.4 vs RA + 7.1 ± 9.0%) in both groups. Conclusion Beneficial vascular remodeling in ET men is associated with lower retrograde shear during external compression. Acute increases in retrograde shear with external compression do not detrimentally impact microvascular oxygenation.

Quantification of aerobic determinants of performance in post-pubertal adolescent middle-distance runners Abstract Purpose The use of oxygen cost ( \(\dot{O}\) aero) parameters to predict endurance performance has recently been criticized. Instead, it is suggested that aerobic energy cost ( \(\dot{E}_{\text{aero}}\) ) provides greater validity; however, a comparison of these quantification methods has not previously been made. Methods Fifty-six male (n = 34) and female (n = 22) competitive adolescent (17 ± 1 years) middle-distance runners participated in a sub-maximal and maximal incremental treadmill test. Running economy (RE) was measured at the speed corresponding to lactate turnpoint, and the three speeds prior. Maximal oxygen uptake ( \(\dot{V}\) O2max), speed at \(\dot{V}\) O2max and fraction of \(\dot{V}\) O2max utilized across a range of intensities, and speeds from 0.8, 1.5 and 3 km races were also quantified. RE and fractional utilization were calculated in units of \(\dot{O}\) aero and \(\dot{E}\) aero. Results Multiple linear regression models demonstrated no discernible difference in the predictive capability of RE, fractional utilization and \(\dot{V}\) O2max when expressed as \(\dot{O}\) aero or \(\dot{E}\) aero in both sexes. When plotted as a function of running speed, \(\dot{O}\) aero displayed a stepwise decrease (F = 11.59, p < 0.001) whereas \(\dot{E}\) aero exhibited a curvilinear response (F = 4.74, p = 0.015). Differences were also evident in the slopes plotted for % \(\dot{V}\) O2max and % \(\dot{E}\) aeromax against running speed (F = 5.38, p = 0.021). Conclusions Quantifying aerobic determinants of performance in units of \(\dot{E}\) aero provides no greater validity compared to \(\dot{O}\) aero-based measurement. Although both \(\dot{E}\) aero and \(\dot{O}\) aero are sensitive to changes in speed, \(\dot{E}\) aero provides the more valid reflection of the underlying metabolic cost of running. Physiologists should also be aware of the potential differences between expression of aerobic running intensity based upon % \(\dot{V}\) O2max compared to % \(\dot{E}\) aeromax.

Vibration as an adjunct to exercise: its impact on shoulder muscle activation Abstract Purpose There is an interest within elite sport in understanding the impact of a vibrating platform as an adjunct to exercise in the training and rehabilitation of throwing athletes. However, there has been no comprehensive evaluation of its impact on the rotator cuff muscles or its effect on the timing of shoulder muscle recruitment more globally. Methods Twenty healthy participants were recruited with EMG recorded from 15 shoulder girdle muscles. Isometric shoulder flexion at 25% maximal voluntary contraction was performed in three testing scenarios [no vibration; whole body vibration (WBV); and arm vibration (AV)]. A press up and triceps dips with and without vibration were also performed. Muscular recruitment was assessed pre- and post-vibration exposure as participants initiated forward flexion. Results Activation of the anterior deltoid (p = 0.002), serratus anterior (p = 0.004), and rotator cuff muscles (p = 0.004–0.022) occurred significantly earlier following exposure to vibration. Significantly greater activation was seen in the anterior, middle and posterior deltoid, upper, middle and lower trapezius, serratus anterior, teres major, latissimus dorsi, supraspinatus, and infraspinatus when the isometric contraction was performed with either WBV and/or AV (p =  < 0.001–0.040). Similarly, increased activation was also demonstrated during the press up and triceps dips when performed with vibration. Conclusion The use of vibration as an adjunct to exercise provokes a near global increase in shoulder muscle activation level. Furthermore, exposure to vibration alters muscular recruitment improving readiness for movement. This has potential implications within elite sport for both training and game preparation; however, further longitudinal work is required.

The effects of 6 weeks of constant-angle muscle stretching training on flexibility and muscle function in men with limited hamstrings’ flexibility Abstract Purpose The aim of the present study was to evaluate the effects of 6 weeks of a constant-angle hamstring muscle flexibility training on muscle–tendon stiffness and the range of motion (ROM) in young men with limited hamstring ROM. Methods 13 participants performed unilateral stretching training (EL), while the contralateral limb acted as control (CL). ROM, relative and peak passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle were assessed before and after the last training session. In addition, participants were tested during the first and last training sessions for first stretch sensation during the stretching procedure only in the EL. Results Straight-leg raise and isokinetic knee ROM tests (both p < 0.0001; from 59.4 ± 8.1 to 70.3 ± 9.8, from 28.3 ± 7.6 to 18.5 ± 5.2, respectively) and peak passive torque (p = 0.001; from 53.1 ± 11.7 to 64.9 ± 12.3) increased only in EL and no changes in relative passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle (p > 0.05) were observed. At the point of first stretch sensation, significant increases in passive torque (p = 0.004) and angle (p < 0.001) were found from pre- to post-training. Conclusion The flexibility training induced significant increases in ROM alongside increases in peak passive torque (stretch tolerance) and the ROM at which stretch was first perceived. However, this occurred without changes in muscle–tendon mechanical properties or transfer to the untrained limb (CL). These results suggest that limb-specific ROM increases were underpinned by neural adaptations.

The ergogenic potency of carbohydrate mouth rinse on endurance running performance of dehydrated athletes Abstract Purpose To examine the effect of carbohydrate (CHO) mouth rinsing on endurance running responses and performance in dehydrated individuals. Methods In a double blind, randomised crossover design, 12 well-trained male runners completed 4 running time to exhaustion (TTE) trials at a speed equivalent to 70% of VO2peak in a thermoneutral condition. Throughout each run, participants mouth rinsed and expectorated every 15 min either 25 mL of 6% CHO or a placebo (PLA) solution for 10 s. The four TTEs consisted of two trials in the euhydrated (EU-CHO and EU-PLA) and two trials in the dehydrated (DY-CHO and DY-PLA) state. Prior to each TTE run, participants were dehydrated via exercise and allowed a passive rest period during which they were fed and either rehydrated equivalent to their body mass deficit (i.e., EU trials) or ingested only 50 mL of water (DY trials). Results CHO mouth rinsing significantly improved TTE performance in the DY compared to the EU trials (78.2 ± 4.3 vs. 76.9 ± 3.8 min, P = 0.02). The arousal level of the runners was significantly higher in the DY compared to the EU trials (P = 0.02). There was no significant difference among trials in heart rate, plasma glucose and lactate, and psychological measures. Conclusions CHO mouth rinsing enhanced running performance significantly more when participants were dehydrated vs. euhydrated due to the greater sensitivity of oral receptors related to thirst and central mediated activation. These results show that level of dehydration alters the effect of brain perception with presence of CHO.

Low-frequency ventilatory oscillations in hypoxia are a major contributor to the low-frequency component of heart rate variability Abstract Purpose Heart rate variability (HRV) may be influenced by several factors, such as environment (hypoxia, hyperoxia, hypercapnia) or physiological demand (exercise). In this retrospective study, we tested the hypothesis that inter-beat (RR) intervals in healthy subjects exercising under various environmental stresses exhibit oscillations at the same frequency than ventilatory oscillations. Methods Spectra from RR intervals and ventilation ( \(\dot{V}\) E) were collected from 37 healthy young male subjects who participated in 5 previous studies focused on ventilatory oscillations (or periodic breathing) during exercise in hypoxia, hyperoxia and hypercapnia. Bland and Altman test and multivariate regressions were then performed to compare respective frequencies and changes in peak powers of the two signals. Results Fast Fourier analysis of RR and \(\dot{V}\) E signals showed that RR was oscillating at the same frequency than periodic breathing, i.e., ~ 0.09 Hz (11 s). During exercise, in these various conditions, the difference between minimum and maximum HRV peak power was positively correlated to the same change in ventilation peak power (P < 0.05). Low-frequency (LF) peak power was correlated to tidal volume (P < 0.01) and breathing frequency (P < 0.001). Conclusions This study suggests that low-frequency ventilatory oscillations in hypoxia are a major contributor to the LF band power of heart rate variability. Clinical Trial Reg. no. NCT02201875.

Independent or simultaneous lowering of core and skin temperature has no impact on self-paced intermittent running performance in hot conditions Abstract Purpose To investigate the effects of lowering core (Tgi) and mean skin temperature (Tsk) concomitantly and independently on self-paced intermittent running in the heat. Methods 10 males (30.5 ± 5.8 years, 73.2 ± 14.5 kg, 176.9 ± 8.0 cm, 56.2 ± 6.6 ml/kg/min) completed four randomised 46-min self-paced intermittent protocols on a non-motorised treadmill in 34.4 ± 1.4 °C, 36.3 ± 4.6% relative humidity. 30-min prior to exercise, participants were cooled via either ice slurry ingestion (INT); a cooling garment (EXT); mixed-cooling (ice slurry and cooling garment concurrently) (MIX); or no-cooling (CON). Results At the end of pre-cooling and the start of exercise Tgi were lower during MIX (36.11 ± 1.3 °C) compared to CON (37.6 ± 0.5 °C) and EXT (36.9 ± 0.5 °C, p < 0.05). Throughout pre-cooling Tsk and thermal sensation were lower in MIX compared to CON and INT, but not EXT (p < 0.05). The reductions in thermophysiological responses diminished within 10–20 min of exercise. Despite lowering Tgi, Tsk, body temperature (Tb), and thermal sensation prior to exercise, the distances covered were similar (CON: 6.69 ± 1.08 km, INT: 6.96 ± 0.81 km, EXT: 6.76 ± 0.65 km, MIX 6.87 ± 0.70 km) (p > 0.05). Peak sprint speeds were also similar between conditions (CON: 25.6 ± 4.48 km/h, INT: 25.4 ± 3.6 km/h, EXT: 26.0 ± 4.94 km/h, MIX: 25.6 ± 3.58 km/h) (p > 0.05). Blood lactate, heart rate and RPE were similar between conditions (p > 0.05). Conclusion Lowering Tgi and Tsk prior to self-paced intermittent exercise did not improve sprint, or submaximal running performance.

Cold-water immersion blunts and delays increases in circulating testosterone and cytokines post-resistance exercise Abstract Introduction Cold-water immersion (CWI) is often used to promote recovery by reducing exercise-induced muscle damage, soreness, and inflammation. However, recent reports have cautioned that CWI may attenuate the adaptive response to resistance training. Purpose To determine the effect of post resistance-exercise CWI on circulating free testosterone (T) and cytokine (IL-6 and TNF-α) response. Methods Using a randomized and counterbalanced repeated-measures design, 11 resistance-trained men completed two workouts (6 sets of 10 repetitions of back squats at 80% of maximum load) a week apart after which they took part in either 15 min of CWI (15 °C) or passive recovery. T, IL-6, and TNFα were measured in blood samples taken before (PRE) and 5 (5POST), 15 (15POST), 30 (30POST), and 60 (60POST) min post-exercise and compared between treatments and over time. Results For T, a significant interaction effect of condition over time (p = 0.030) as well as greater relative concentrations of T in CON (Δ9.2%) than CWI (Δ-0.5%, p = 0.049) at 30POST were observed. In addition, at 60POST, T dropped below PRE values in CWI (Δ-10.4%, p = 0.028) but not in CON (Δ-1.6%, p = 0.850). A suppressed cytokine response was observed after CWI in IL-6 at 30POST (CWI: Δ4.9%, CON: Δ47.5%, p = 0.041) and TNFα at 15POST (CWI: Δ5.3%, CON: Δ17.0%, p = 0.022). Conclusions CWI blunted the T and cytokine response after a bout of resistance exercise. These results indicate that CWI results in an altered anabolic response and may help to explain the previous observation of attenuated hypertrophy when CWI is used after resistance exercise.

Leg- vs arm-cycling repeated sprints with blood flow restriction and systemic hypoxia Abstract Purpose The aim was to compare changes in peripheral and cerebral oxygenation, as well as metabolic and performance responses during conditions of blood flow restriction (BFR, bilateral vascular occlusion at 0% vs. 45% of resting pulse elimination pressure) and systemic hypoxia (~ 400 m, FIO2 20.9% vs. ~ 3800 m normobaric hypoxia, FIO2 13.1 ± 0.1%) during repeated sprint tests to exhaustion (RST) between leg- and arm-cycling exercises. Methods Seven participants (26.6 ± 2.9 years old; 74.0 ± 13.1 kg; 1.76 ± 0.09 m) performed four sessions of RST (10-s maximal sprints with 20-s recovery until exhaustion) during both leg and arm cycling to measure power output and metabolic equivalents as well as oxygenation (near-infrared spectroscopy) of the muscle tissue and prefrontal cortex. Results Mean power output was lower in arms than legs (316 ± 118 vs. 543 ± 127 W; p < 0.001) and there were no differences between conditions for a given limb. Arms demonstrated greater changes in concentration of deoxyhemoglobin (∆[HHb], − 9.1 ± 6.1 vs. − 6.5 ± 5.6 μm) and total hemoglobin concentration (∆[tHb], 15.0 ± 10.8 vs. 11.9 ± 7.9 μm), as well as the absolute maximum tissue saturation index (TSI, 62.0 ± 8.3 vs. 59.3 ± 8.1%) than legs, respectively (p < 0.001), demonstrating a greater capacity for oxygen extraction. Further, there were greater changes in tissue blood volume [tHb] during BFR only compared to all other conditions (p < 0.01 for all). Conclusions The combination of BFR and/or hypoxia led to increased changes in [HHb] and [tHb] likely due to greater vascular resistance, to which arms were more responsive than legs.

Bone mineral density, energy availability, and dietary restraint in collegiate cross-country runners and non-running controls Abstract Purpose Weight-bearing activities such as running have been shown to be osteogenic. However, investigations have also shown that running may lead to site-specific deficiencies in bone mineral density (BMD) as well as overall low BMD. The purpose of this investigation was to evaluate and compare the BMD of female and male collegiate cross-country runners with non-running controls. In addition, energy availability and disordered eating attitudes and behaviors were assessed. Methods BMD of 60 collegiate cross-country runners and 47 BMI and age-matched non-running controls were measured via DXA scans. Participants completed a Block 2014 Food Frequency Questionnaire and Eating Disorder Examination Questionnaire. Results Controlling for fat-free mass (FFM), male runners showed greater BMD at the femoral neck (0.934 ± 0.029 vs. 0.866 ± 0.028 g cm2, p < 0.05), total hip (1.119 ± 0.023 vs. 1.038 ± 0.021 g cm2, p < 0.05), and whole body (1.119 ± 0.023 vs. 1.038 ± 0.021 g cm2, p < 0.05) than male controls. The female runners had greater whole-body BMD than female controls (1.143 ± 0.018 vs. 1.087 ± 0.022 g cm2, p < 0.05). Runners scored significantly higher than controls in dietary restraint (1.134 ± 1.24 vs. 0.451 ± 0.75, p < 0.05), male runners were significantly higher than male controls in eating concern (1.344 ± 1.08 vs. 0.113 ± 0.27, p < 0.05) and female runners were significantly higher than male runners in shape concern (1.056 ± 1.27 vs. 0.242 ± 0.31, p < 0.05). Forty-two percent of the male runners and 29% of female runners had an energy availability of less than 30 kcals kg−1FFM. Conclusion It appears that distance running has beneficial effects on whole-body BMD and site-specific areas. Further research is warranted to further clarify the health effects of eating behaviors and EA of distance runners.