Let’s all play with the same rules

Poor statistical reporting and spin in neuromuscular fatigue research

Physiological adaptations to repeated sprint training in hypoxia induced by voluntary hypoventilation at low lung volume Abstract Purpose This study investigated the effects of repeated-sprint (RS) training in hypoxia induced by voluntary hypoventilation at low lung volume (RSH-VHL) on physiological adaptations, RS ability (RSA) and anaerobic performance. Methods Over a 3-week period, eighteen well-trained cyclists completed six RS sessions in cycling either with RSH-VHL or with normal conditions (RSN). Before (Pre) and after (Post) the training period, the subjects performed an RSA test (10 × 6-s all-out cycling sprints) during which oxygen uptake \(\left( {{\dot{\text{V}}\text{O}}_{2} } \right)\) and the change in both muscle deoxyhaemoglobin (Δ[HHb]) and total haemoglobin (Δ[THb]) were measured. A 30-s Wingate test was also performed and maximal blood lactate concentration ([La]max) was assessed. Results At Post compared to Pre, the mean power output during both the RSA and the Wingate tests was improved in RSH-VHL (846 ± 98 vs 911 ± 117 W and 723 ± 112 vs 768 ± 123 W, p < 0.05) but not in RSN (834 ± 52 vs 852 ± 69 W, p = 0.2; 710 ± 63 vs 713 ± 72 W, p = 0.68). The average \({\dot{{\text{V}}}{{\text{O}}}}_{2}\) recorded during the RSA test was significantly higher in RSH-VHL at Post but did not change in RSN. No change occurred for Δ[THb] whereas Δ[HHb] increased to the same extent in both groups. [Lamax] after the Wingate test was higher in RSH-VHL at Post (13.9 ± 2.8 vs 16.1 ± 3.2 mmol L−1, p < 0.01) and tended to decrease in RSN (p = 0.1). Conclusions This study showed that RSH-VHL could bring benefits to both RSA and anaerobic performance through increases in oxygen delivery and glycolytic contribution. On the other hand, no additional effect was observed for the indices of muscle blood volume and O2extraction.

Impact of 3-day high and low dietary sodium intake on sodium status in response to exertional-heat stress: a double-blind randomized control trial Abstract Purpose To determine the impact of altering dietary sodium intake for 3 days preceding exercise on sweat sodium concentration [Na+], and cardiovascular and thermoregulatory variables. Methods Fifteen male endurance athletes (runners n = 8, cyclists n = 7) consumed a low (LNa, 15 mg kg−1 day−1) or high (HNa, 100 mg kg−1 day−1) sodium diet, or their usual free-living diet [UDiet, 46 (37–56) mg kg−1 day−1] for 3 days in a double-blind, randomized cross-over design, collecting excreted urine (UNa) and refraining from exercise. On day 4, they completed 2 h running at 55% \(\dot{V}\) O2max or cycling at 55% maximum aerobic power in Tamb 35 °C. Pre- and post-exercise blood samples were collected, and sweat from five sites using absorbent patches along the exercise protocol. Results UNa on days 2–3 pre-exercise [mean (95% CI) LNa 16 (12–19) mg kg−1 day−1, UDiet 46 (37–56) mg kg−1 day−1, HNa 79 (72–85) mg kg−1 day−1; p < 0.001] and pre-exercise aldosterone [LNa 240 (193–286) mg kg−1 day−1, UDiet 170 (116–224) mg kg−1 day−1, HNa 141 (111–171) mg kg−1 day−1; p = 0.001] reflected sodium intake as expected. Pre-exercise total body water was greater following HNa compared to LNa (p < 0.05), but not UDiet. Estimated whole-body sweat [Na+] following UDiet was 10–11% higher than LNa and 10–12% lower than HNa (p < 0.001), and correlated with pre-exercise aldosterone (1st h r =  − 0.568, 2nd h r =  − 0.675; p < 0.01). Rectal temperature rose more quickly in LNa vs HNa (40–70 min; p < 0.05), but was similar at the conclusion of exercise, and no significant differences in heart rate or perceived exertion were observed. Conclusions Three day altered sodium intake influenced urinary sodium excretion and sweat [Na+], and the rise in rectal temperature, but had no effect on perceived exertion during moderate-intensity exercise in hot ambient conditions.

Unilateral hamstrings static stretching can impair the affected and contralateral knee extension force but improve unilateral drop jump height Abstract Purpose Prolonged static stretching (SS) in isolation (no dynamic warm-up) can impair muscle performance. There are conflicting reports whether impairments are present in antagonist and contralateral muscles. The objective of this study was to assess the effect of unilateral hamstrings SS on ipsilateral stretched and contralateral limbs’ strength and jump power. Methods The SS (four repetitions of 30-s) and control sessions involved unilateral testing of the stretched leg and contralateral leg for knee extension (KE) maximum voluntary isometric contraction (MVIC) force and electromyography (EMG), drop jump (DJ) height and contact time at 1-min post-stretching. Results There were significant KE MVIC force impairments for both the SS (p = 0.006, d = 0.3, − 8.1%) and contralateral (p = 0.02, d = 0.20, − 4.2%) leg. With normalized data, there was a near-significant (p = 0.1), small magnitude (d = 0.29), greater force impairment with the ipsilateral (93.0 ± 12.8% of pre-test) versus the contralateral (96.2 ± 9.1% of pre-test) KE MVIC force. DJ height significantly improved for the stretched leg (p = 0.03, d = 0.18, + 9.2%) with near-significant, improvements for the contralateral leg (p = 0.06, d = 0.22, + 12.1%). For the stretched leg, DJ contact time was significantly (p = 0.04, d = 0.18, + 3.4%) prolonged, but there was no significant change with the contralateral leg. Conclusions Unilateral hamstrings SS induced strength deficits in the ipsilateral and contralateral knee extension MVIC and a prolongation of the stretched leg DJ contact period. In anticipation of maximal force outputs, prolonged SS in isolation (no dynamic warm-up included) can have negative consequences on antagonist and contralateral muscle performance.

The effect of an ultra-endurance running race on heart rate variability Abstract Purpose The aim of this study was to investigate the effect of an ultra-marathon on heart rate variability (HRV) and psychometric indices in endurance runners. In addition, we aimed to determine the magnitude of change and subsequent recovery for 7 days following the race. Methods Recreationally trained runners (n = 13 (8M); age = 36.6 ± 7.6 years; height = 174 ± 9 cm; weight = 70.5 ± 9.3 kg) completed measures of HRV upon waking in the morning for 1 week prior to and 1 week following a 64-km running race. Profile of mood states, wellbeing, and muscular soreness were also measured throughout the study period to further contextualise recovery. Results An increase in heart rate accompanied by decreased LnSDNN, LnRMSSD, LnLF, LnHF, and LnLF/HF from baseline were observed 1 day post-race (p < 0.05). Indices of HRV had returned to baseline on day 2 of recovery. Perceptual fatigue and muscle soreness increased post-race (immediately following and on day 1 of recovery) (p < 0.05) and took until day 5 of recovery to return to baseline. Conclusion The results indicate that cardiac autonomic control is significantly altered in response to a 64 km ultra-marathon. Specifically, parasympathetic activity is suppressed. The change in autonomic control was relatively short-lived, and parasympathetic-related indices had returned to baseline 2 days after the event. Subjective measures of fatigue and wellbeing suggest that athletes were not completely recovered until day 5 post-event, with muscular soreness remaining prominent during this period. A combination of physiological and psychological parameters is important to contextualise recovery in ultra-endurance runners.

Treadmill running using an RPE-clamp model: mediators of perception and implications for exercise prescription Abstract Purpose The mediators of the perception of effort during exercise are still unclear. The aim of the present study was to examine physiological responses during runs using a rating of perceived exertion (RPE)-clamp model at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above GET (RPEGET+15%) to identify potential mediators and performance applications for RPE during treadmill running. Methods Twenty-one runners ( \({\dot{V}\mathrm{O}}_{2}\) max = 51.7 ± 8.3 ml kg−1 min−1) performed a graded exercise test to determine maximal oxygen consumption and the RPE associated with GET and GET + 15% followed by randomized 60 min RPE-clamp runs at RPEGET and RPEGET+15%. Mean differences for \({\dot{V}\mathrm{O}}_{2}\) , heart rate (HR), minute ventilation ( \({\dot{V}}_{E}\) ), respiratory frequency ( \({\mathcal{F}}_{R})\) , respiratory exchange ratio (RER), and velocity were compared across each run. Results After minute 14, \({\dot{V}\mathrm{O}}_{2}\) , RER and velocity did not differ across conditions, but decreased across time (p < 0.05). There was a significant (p < 0.05) condition × time interaction for \({\dot{V}}_{E}\) , where values were significantly higher during RPE-clamp runs at RPEGET+15% and decreased across time in both conditions. There were no differences across condition or time for HR, and only small difference between conditions for \({\mathcal{F}}_{R}\) . Conclusions HR and \({\mathcal{F}}_{R}\) may play a role in mediating the perception of effort, while \({\dot{V}\mathrm{O}}_{2}\) , RER, and \({\dot{V}}_{E}\) may not. Although HR and \({\mathcal{F}}_{R}\) may mediate the maintenance of a perceptual intensity, they may not be sensitive to differentiate perceptual intensities at GET and GET + 15%. Thus, prescribing exercise using an RPE-clamp model may only reflect a sustainable \({\dot{V}\mathrm{O}}_{2}\) within the moderate intensity domain.

Effects of upper-body, lower-body, or combined resistance training on the ratio of follistatin and myostatin in middle-aged men Abstract Purpose Due to the mechanistic role of myostatin and follistatin in modulating muscle mass, shifts in the follistatin to myostatin ratio (F:M) may help explain changes in muscular size in response to resistance training (RT). The present study examined whether differential responses in follistatin and myostatin occur based on the amount of active musculature in a RT program in middle-aged men. Methods Forty middle-aged men (age = 46.5 ± 3.1 years) were randomly assigned to 1 of 4 groups, upper-body RT (UB; n = 10), lower-body RT (LB; n = 10), combined RT (UB + LB; n = 10) or control (C; n = 10). The training protocol consisted of three exercise sessions per week for 8 weeks. Blood samples were obtained at baseline and 48 h after the final session of the training program. Results Muscle mass significantly increased (p < 0.05) following UB = 0.76 ± 0.46 kg, LB = 0.90 ± 0.29 kg, UB + LB = 1.38 ± 0.70 kg, compared to no changes after control. Serum follistatin increased in the LB = 0.24 ± 0.06 ng mL−1, UB = 0.27 ± 0.17 ng mL−1, UB + LB = 0.50 ± 0.18 ng mL−1, while serum myostatin decreased in the LB = − 0.11 ± 0.08 ng mL−1 and UB + LB = − 0.34 ± 0.23 ng mL−1, but not UB = 0.07 ± 0.16 ng mL−1. Further, change in concentration following training was larger between UB + LB and either LB or UB alone for both follistatin and myostatin. Conclusions Both UB and LB increase muscle mass and alter the F: M ratio; however, the change in these endocrine markers is approximately twice as large if UB and LB is combined. The endocrine response to RT of myostatin and follistatin may depend on the volume of muscle mass activated during training.

Isometric-based test improves EMG-threshold determination in boys vs. men Abstract Background Children have been hypothesized to utilize higher-threshold (type-II) motor units (MUs) to a lesser extent than adults. Two recent studies, using a cycling-based EMG-threshold (EMGTh) protocol, supported the hypothesis, showing children’s EMGTh intensities to be higher than adults’. Conclusions, however, were hampered by children’s low EMGTh detection rates. Insufficiently high contractile forces at exhaustion were postulated as the reason for non-detection, predominantly in children. An intermittent isometric contraction test (IICT) protocol facilitates higher contractile forces prior to exhaustion and was shown effective in EMGTh testing of adults. Purpose Determine whether an IICT protocol would enhance EMGTh detection in children, and consequently increase the magnitude of the previously observed child–adult EMGTh differences. Methods 18 boys and 21 men completed one-repetition-maximum (1RM) isometric knee-extension test. The IICT protocol followed, commencing at 25%1RM and comprising five isometric contractions per load, incremented by ~ 3%1RM to exhaustion. Vastus lateralis surface EMG was recorded and EMGTh, expressed as %1RM, was defined as the onset of the EMG-response’s steeper segment. Results EMGTh was detected in 88.9% of boys and 95.2% of men, and occurred at higher relative intensities in boys (56.4 ± 9.2%1RM) than in men (46.0 ± 6.8%1RM). This 10.4% difference was 57% greater than the corresponding, previously reported cycling-based age-related difference. Conclusions With the boys’ detection rate nearly on par with the men’s, the IICT protocol appears to overcome much of the intensity limitation of cycling-based protocols and provide a more sensitive EMGTh detection tool, thus extending the previously observed boys‒men difference. This difference adds supports to the notion of children’s more limited type-II MU recruitment capacity.

Experimental knee-related pain enhances attentional interference on postural control Abstract Purpose To quantify how postural stability is modified during experimental pain while performing different cognitively demanding tasks. Methods Sixteen healthy young adults participated in the experiment. Pain was induced by intramuscular injection of hypertonic saline solution (1 mL, 6%) in both vastus medialis and vastus lateralis muscles (0.9% isotonic saline was used as control). The participants stood barefoot in tandem position for 1 min on a force plate. Center of pressure (CoP) was recorded before and immediately after injections, while performing two cognitive tasks: (i) counting forwards by adding one; (ii) counting backwards by subtracting three. CoP variables—total area of displacement, velocity in anterior–posterior (AP-velocity) and medial–lateral (ML-velocity) directions, and CoP sample entropy in anterior–posterior and medial–lateral directions were displayed as the difference between the values obtained after and before each injection and compared between tasks and injections. Results CoP total area ( − 84.5 ± 145.5 vs. 28.9 ± 78.5 cm2) and ML-velocity ( − 1.71 ± 2.61 vs. 0.98 ± 1.93 cm/s) decreased after the painful injection vs. Control injection while counting forward (P < 0.05). CoP total area (12.8 ± 53.9 vs. − 84.5 ± 145.5 cm2), ML-velocity ( − 0.34 ± 1.92 vs. − 1.71 ± 2.61 cm/s) and AP-velocity (1.07 ± 2.35 vs. − 0.39 ± 1.82 cm/s) increased while counting backwards vs. forwards after the painful injection (P < 0.05). Conclusion Pain interfered with postural stability according to the type of cognitive task performed, suggesting that pain may occupy cognitive resources, potentially resulting in poorer balance performance.