Acute acetaminophen ingestion improves performance and muscle activation during maximal intermittent knee extensor exercise

Resistance training increases myofibrillar protein synthesis in middle-to-older aged adults consuming a typical diet with no influence of protein source: a randomized controlled trial

BACKGROUND

The primary protein source of a diet may impact skeletal muscle maintenance with advancing age. The impact of the animal and plant protein content of a typical protein-containing diet on muscle anabolism in middle-to-older aged adults is unknown.

OBJECTIVES

To determine muscle adaptive remodelling response to a 10-day dietary intervention containing divergent protein sources, with and without resistance exercise training (RET) in middle-to-older aged adults.

METHODS

In a single-blind randomized control trial, twenty-seven 50-70-year-old participants consumed 1.0g·kg BM-1·day-1 of protein from an animal-focused whey protein-supplemented diet (AW-D) or plant-focused pea protein-supplemented diet (PP-D). Throughout the 10-day diet intervention, unilateral knee extensor RET was performed every other day. Deuterated water ingestion and skeletal muscle biopsies enabled measurement of daily integrated myofibrillar protein synthesis (iMyoPS) rates in the trained, and untrained legs. Changes in metabolic rate, body composition, lipid profiles, renal function, whole-body nitrogen balance (WBNB), strength and muscle architecture were also determined.

RESULTS

Daily iMyoPS rates were significantly greater (P<0.001) in the trained compared to the untrained leg for AW-D (1.44 ± 0.26 vs 1.29 ± 0.27 %⋅day-1) and PP-D (1.50 ± 0.17 vs 1.34 ± 0.21 %⋅day-1) with no differences between groups, within leg. Training and diet did not affect intracellular anabolic signalling, muscle architecture, strength, metabolic rate, renal function or WBNB. Serum non-HDL cholesterol was significantly (P=0.014) lower following the intervention for PP-D only (pre: 3.89 ± 0.84, post 3.37 ± 0.78 mmol⋅L) with no other changes in lipid profiles.

CONCLUSIONS

The 10-day provision of 1.0g·kg BM-1·day-1 from predominantly plant-derived or animal-derived protein does not influence daily iMyoPS rates in middle-to-older aged adults and has little impact on metabolic and renal health parameters. RET enhances rates of daily iMyoPS in middle-to-older aged adults consuming a typical protein-containing diet, with no influence of protein source.

CLINICAL TRIAL REGISTRY NUMBER

ClinicalTrials.gov NCT05574205 https://clinicaltrials.gov/study/NCT05574205.

Acute acetaminophen ingestion improves the recovery of neuromuscular fatigue following simulated soccer match-play

OBJECTIVES

This study aimed to investigate the impact of acute acetaminophen ingestion on the responses of neuromuscular function, biomarkers of muscle damage, and physical performance during the 72-hour recovery period following simulated soccer match-play.

DESIGN

The study followed a crossover randomized, double-blind, placebo-controlled trial design.

METHODS

During the two experimental sessions, thirteen semi-professional male soccer players completed a 90-minute simulated soccer match, 60 min after oral ingestion of 1 g acetaminophen or placebo. Maximal voluntary contraction and twitch responses of the knee extensor muscles, elicited through electrical femoral nerve stimulation, were utilized to evaluate both peripheral fatigue (potentiated twitch force, Qtw,pot) and central fatigue (voluntary activation). Performance was assessed through countermovement jump and 20 m sprint tests. Creatine kinase and lactate dehydrogenase were also measured.

RESULTS

Smaller reductions were observed in maximal voluntary contraction (-13.3 ± 7.5 % vs. -24.7 ± 11.1 %) and voluntary activation (-3.8 ± 4.4 % vs. -12.9 ± 5.4 %) in the acetaminophen compared to the placebo condition immediately after simulated soccer match-play (p < 0.05). Afterward, these parameters were recovered 24 h earlier in the acetaminophen session compared to the placebo session. Furthermore, the 20 m sprint performance was significantly better throughout the recovery period in the acetaminophen session compared to the placebo session.

CONCLUSIONS

The findings of this study showed that acute ingestion of 1 g of acetaminophen (1 h before exercise) attenuated the decrease in maximal voluntary contraction and voluntary activation levels after exercise, as well as improved 20 m sprint performance.

Caffeine, but not paracetamol (acetaminophen), enhances muscular endurance, strength, and power

BACKGROUND

Caffeine is one of the most popular ergogenic aids consumed by athletes. Caffeine's ergogenic effect has been generally explained by its ability to bind to adenosine receptors, thus modulating pain and reducing perceived exertion. Another pharmacological agent that may improve performance due to its analgesic proprieties is paracetamol. This study aimed to explore the effects of caffeine, paracetamol, and caffeine + paracetamol consumption on muscular endurance, strength, power, anaerobic endurance, and jumping performance.

METHODS

In this randomized, crossover, double-blind study, 29 resistance-trained participants (11 men and 18 women) ingested either a placebo, caffeine (3 mg/kg), paracetamol (1500 mg) or caffeine + paracetamol 45 min before the testing sessions. The testing sessions included performing the bench press exercise with 75% of one-repetition maximum to momentary muscular failure, isokinetic knee extension and flexion at angular velocities of 60°/sec and 180°/sec, Wingate, and countermovement jump (CMJ) tests.

RESULTS

Compared to placebo, isolated caffeine ingestion increased the number of repetitions performed in the bench press (p = 0.005; d = 0.42). Compared to placebo, isolated caffeine ingestion and/or caffeine + paracetamol consumption was ergogenic for strength (torque), muscular endurance (total work), or power in the isokinetic assessment, particularly at slower angular velocities (p = 0.027 to 0.002; d = 0.16 to 0.26). No significant differences between the conditions were observed for outcomes related to the Wingate and CMJ tests.

CONCLUSION

This study provided novel evidence into the effectiveness of caffeine, paracetamol, and their combination on exercise performance. We found improvements in muscular endurance, strength, or power only when caffeine was consumed in isolation, or in combination with paracetamol. Isolated paracetamol consumption did not improve performance for any of the analyzed outcomes, thus calling into question its ergogenic potential.

Acute ingestion of acetaminophen improves cognitive and repeated high intensity short-term maximal performance in well-trained female athletes: a randomized placebo-controlled trial

This study examined the effect of acute acetaminophen (ACTP) ingestion on physical performance during the 5 m shuttle run test (5mSRT), attention, mood states, and the perception of perceived exertion (RPE), pain (PP), recovery (PRS), and delayed onset of muscle soreness (DOMS) in well-trained female athletes. In a randomized, placebo-controlled, double-blind, crossover trial, fifteen well-trained female athletes (age 21 ± 2 years, height 165 ± 6 cm, body mass 62 ± 5 kg) swallowed either 1.5 g of ACTP or 1.5 g of placebo. The profile of mood states (POMS) and digit cancellation (DCT) were assessed 45 min postingestion, and 5mSRT was performed 60 min postingestion. The RPE and PP were determined immediately after each 30-s repetition of the 5mSRT, and the PRS and DOMS were recorded at 5 min and 24 h post-5mSRT. For the 5mSRT, ACTP ingestion improved the greatest distance (+ 10.88%, p < 0.001), total distance (+ 11.33%, p = 0.0007) and fatigue index (+ 21.43%, p = 0.0003) compared to PLA. Likewise, the DCT score was better on the ACTP (p = 0.0007) than on the PLA. RPE, PP, PRS, and DOMS scores were improved after ACTP ingestion (p < 0.01 for all comparisons) compared to PLA. POMS scores were enhanced with ACTP ingestion compared to PLA (p < 0.01). In conclusion, this study indicates that acute acetaminophen ingestion can improve repeated high intensity short-term maximal performance, attention, mood states, and perceptions of exertion, pain, recovery, and muscle soreness in well-trained female athletes, suggesting potential benefits for their overall athletic performance and mood state.

Greater myofibrillar protein synthesis following weight-bearing activity in obese old compared with non-obese old and young individuals

The mechanisms through which obesity impacts age-related muscle mass regulation are unclear. In the present study, rates of integrated myofibrillar protein synthesis (iMyoPS) were measured over 48-h prior-to and following a 45-min treadmill walk in 10 older-obese (O-OB, body fat[%]: 33 ± 3%), 10 older-non-obese (O-NO, 20 ± 3%), and 15 younger-non-obese (Y-NO, 13 ± 5%) individuals. Surface electromyography was used to determine thigh muscle "activation". Quadriceps cross-sectional area (CSA), volume, and intramuscular thigh fat fraction (ITFF) were measured by magnetic resonance imaging. Quadriceps maximal voluntary contraction (MVC) was measured by dynamometry. Quadriceps CSA and volume were greater (muscle volume, Y-NO: 1182 ± 232 cm3; O-NO: 869 ± 155 cm3; O-OB: 881 ± 212 cm3, P < 0.01) and ITFF significantly lower (m. vastus lateralis, Y-NO: 3.0 ± 1.0%; O-NO: 4.0 ± 0.9%; O-OB: 9.1 ± 2.6%, P ≤ 0.03) in Y-NO compared with O-NO and O-OB, with no difference between O-NO and O-OB in quadriceps CSA and volume. ITFF was significantly higher in O-OB compared with O-NO. Relative MVC was lower in O-OB compared with Y-NO and O-NO (Y-NO: 5.5 ± 1.6 n·m/kg-1; O-NO: 3.9 ± 1.0 n·m/kg-1; O-OB: 2.9 ± 1.1 n·m/kg-1, P < 0.0001). Thigh muscle "activation" during the treadmill walk was greater in O-OB compared with Y-NO and O-NO (Y-NO: 30.5 ± 13.5%; O-NO: 35.8 ± 19.7%; O-OB: 68.3 ± 32.3%, P < 0.01). Habitual iMyoPS did not differ between groups, whereas iMyoPS was significantly elevated over 48-h post-walk in O-OB (+ 38.6 ± 1.2%·day-1, P < 0.01) but not Y-NO or O-NO (+ 11.4 ± 1.1%·day-1 and + 17.1 ± 1.1%·day-1, respectively, both P > 0.271). Equivalent muscle mass in O-OB may be explained by the muscle anabolic response to weight-bearing activity, whereas the age-related decline in indices of muscle quality appears to be exacerbated in O-OB and warrants further exploration.

Peripheral fatigue regulation during knee extensor exercise in type 1 diabetes and consequences on the force-duration relationship

PURPOSE

This study aimed to examine if peripheral fatigue is adjusted during knee extensor (KE) exercise in order not to surpass a critical threshold patient with type 1 diabetes (T1D) and the consequences of this mechanism on the force-duration relationship.

METHODS

Eleven T1D individuals randomly performed two different sessions in which they performed 60 maximum voluntary contractions (MVC; 3 s contraction, 2 s relaxation). One trial was performed in the non-fatigued state (CTRL) and another after fatiguing neuromuscular stimulation of the KE (FNMES). Peripheral and central fatigue were quantified by the difference between pre and post exercise in quadriceps voluntary activation (ΔVA) and potentiated twitch (ΔPtw). Critical torque (CT) was determined as the average force of the last 12 contractions, whereas W' was calculated as the area above the CT.

RESULTS

Although FNMES led to a significant decrease in potentiated twitch (Ptw) before performing the 60-MVCs protocol (p < 0.05), ΔVA (∼ -7.5%), ΔPtw (∼ -39%), and CT (∼816 N) post-MVCs were similar between the two conditions. The difference in W' between CTRL and FNMES was correlated with the level of pre-fatigue induced in FNMES (r2 = 0.60). In addition, W' was correlated with ΔPtw (r2 = 0.62) in the CTRL session.

CONCLUSION

Correlative results in the present study indicate that regulating peripheral fatigue mechanisms at a critical threshold limit W'. Additionally, peripheral fatigue during KE exercise is limited to an individual threshold in T1D patients.

Tramadol is a performance-enhancing drug in highly trained cyclists: a randomized controlled trial

Tramadol is a potent narcotic analgesic reportedly used in multiple sports to reduce exertional pain and confer a performance advantage. This study sought to identify whether tramadol enhances performance in time trial cycling. Twenty-seven highly trained cyclists were screened for tramadol sensitivity and then attended the laboratory across three visits. Visit 1 identified maximal oxygen uptake, peak power output, and gas exchange threshold through a ramp incremental test. Participants returned to the laboratory on two further occasions to undertake cycling performance tests following the ingestion of either 100 mg of soluble tramadol or a taste-matched placebo control in a double-blind, randomized, and crossover design. In the performance tests, participants completed a 30 min non-exhaustive fixed intensity cycling task at a heavy exercise intensity (272 ± 42 W), immediately followed by a competitive self-paced 25-mile time trial (TT). Following removal of two outlier data sets, analysis was completed on n = 25. Participants completed the TT significantly faster (d = 0.54, P = 0.012) in the tramadol condition (3758 s ± 232 s) compared with the placebo condition (3808 s ± 248 s) and maintained a significantly higher mean power output (+9 W) throughout the TT (ηp2 = 0.262, P = 0.009). Tramadol reduced perception of effort during the fixed intensity trial (P = 0.026). The 1.3% faster time in the tramadol condition would be sufficient to change the outcomes of a race and is highly meaningful and pervasive in this cohort of highly trained cyclists. The data from this study suggests that tramadol is a performance-enhancing drug.NEW & NOTEWORTHY In the current study, when cycling with tramadol participants completed a time trial on average 50 s faster and at a 9 W higher power output than the placebo control. The study used both a fixed intensity and self-paced time trial exercise tasks to reflect the demands of a stage race. The outcomes from this study were used by the World Anti-Doping Agency to inform their addition of tramadol to the Prohibited List in 2024.

Interaction of Factors Determining Critical Power

The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical settings. The asymptote of the hyperbolic relation between external power and time to task failure, critical power, represents the threshold intensity above which systemic and intramuscular metabolic homeostasis can no longer be maintained. After ~ 60 years of research into the phenomenon of critical power, a clear understanding of its physiological determinants has emerged. The purpose of the present review is to critically examine this contemporary evidence in order to explain the physiological underpinnings of critical power. Evidence demonstrating that alterations in convective and diffusive oxygen delivery can impact upon critical power is first addressed. Subsequently, evidence is considered that shows that rates of muscle oxygen utilisation, inferred via the kinetics of pulmonary oxygen consumption, can influence critical power. The data reveal a clear picture that alterations in the rates of flux along every step of the oxygen transport and utilisation pathways influence critical power. It is also clear that critical power is influenced by motor unit recruitment patterns. On this basis, it is proposed that convective and diffusive oxygen delivery act in concert with muscle oxygen utilisation rates to determine the intracellular metabolic milieu and state of fatigue within the myocytes. This interacts with exercising muscle mass and motor unit recruitment patterns to ultimately determine critical power.

Exercise-Induced Fatigue in Hamstring versus Quadriceps Muscles and Consequences on the Torque-Duration Relationship in Men

PURPOSE

The present study investigated the mechanisms of neuromuscular fatigue in quadriceps and hamstring muscles and its consequences on the torque-duration relationship.

METHODS

Twelve healthy men performed a 5-min all-out exercise (3-s contraction, 2-s relaxation) with either quadriceps or hamstring muscles on separate days. Central fatigue and peripheral fatigue were quantified via changes in pre- to postexercise voluntary activation (VA) and potentiated twitch (P Tw ) torque evoked by supramaximal electrical stimulation, respectively. Critical torque was determined as the mean torque of the last six contractions, whereas W ' was calculated as the torque impulse done above critical torque.

RESULTS

After exercise, maximal voluntary contraction (MVC) decreased to a greater magnitude ( P < 0.001) in quadriceps (-67% ± 9%) compared with hamstring (-51% ± 10%). ∆P Tw was also greater in quadriceps compared with hamstring (-69% ± 15% vs 55% ± 10%, P < 0.01), whereas central fatigue only developed in quadriceps (∆VA, -25% ± 28%). Hamstring demonstrated reduced critical torque compared with quadriceps (60 ± 12 vs 97 ± 26 N·m, P < 0.001) as well as drastically lower W ' (1001 ± 696 vs 8111 ± 2073 N·m·s, P < 0.001). No correlation was found between quadriceps and hamstring for any index of neuromuscular fatigue (∆MVC, ∆P Tw , or ∆VA).

CONCLUSIONS

These findings revealed that hamstring presented different etiology and magnitude of neuromuscular fatigue compared with quadriceps. The absence of correlation observed between quadriceps and hamstring fatigue parameters (∆MVC, ∆P Tw , or ∆VA) suggests no interrelation in fatigue etiology between these two muscle groups within individuals and, therefore, highlights the need to investigate specifically hamstring muscle fatigue.

What is the Effect of Paracetamol (Acetaminophen) Ingestion on Exercise Performance? Current Findings and Future Research Directions

In recent years, studies have explored the effects of paracetamol (acetaminophen) ingestion on exercise performance. However, due to the contrasting findings, there is still no consensus on this topic. This article provides an overview of the effects of paracetamol on endurance, sprinting, and resistance exercise performance. Studies have reported that paracetamol ingestion may be ergogenic for endurance performance. These effects occur when paracetamol is ingested 45-60 min before exercise and appear to be more pronounced in time-to-exhaustion versus time-trial tests. Besides endurance, paracetamol ingestion 30 min before exercise increases mean power during repeated cycling sprints in interval training involving repeated 30-s all-out bouts. Preliminary data on paracetamol ingestion also suggest: (a) improved endurance performance in the heat; (b) an improvement in single sprint performance, at least when paracetamol is ingested following exercise-induced fatigue; and (c) attenuation of the decline in muscular strength that occurs with repeated maximum contractions. An ergogenic effect of paracetamol is most commonly observed when a dose of 1500 mg is ingested 30-60 min before exercise. Despite these performance-enhancing effects, the aim of this article is not to promote paracetamol use, as side effects associated with its consumption and ethical aspects need to be considered before utilizing paracetamol as an ergogenic aid. Future research on this topic is still needed, particularly related to paracetamol dosing, timing of ingestion, and the effects of paracetamol in females and elite athletes.

Paracetamol: unconventional uses of a well-known drug

OBJECTIVES

To describe and map what is known about unconventional uses of paracetamol through a scoping review of published literature by adopting adopted a PRISMA systematic approach methodology.

KEY FINDINGS

Four themes for unconventional uses of paracetamol emerged: (a) use of paracetamol in sleep (a-1) positive effect of paracetamol on sleep (n = 9) or (a-2) neutral or negative effect of paracetamol on sleep (n = 9); (b) use of paracetamol in sport (n = 13); (c) mixing paracetamol with drinks, waterpipe and illicit drugs (n = 5); and (d) miscellaneous uses (n = 4). Forty records were reviewed and charted. Available literature supports concern around the potential of harmful or non-medical use of paracetamol, especially among patients with a history of substance use, parents of young children or athletes.

SUMMARY

Paracetamol (acetaminophen) is one of the most popular and widely used drugs for the treatment of pain and fever. It is considered remarkably safe if used within instructions. However, there is growing evidence that paracetamol, is sometimes used outside approved indications or abused (i.e. used for non-medical reasons). This review highlights the need for enhanced pharmacovigilance and surveillance of non-medical paracetamol use and raising general public awareness of its potential dangers especially in higher than recommended doses.

Effects of Paracetamol (Acetaminophen) Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis

Several studies explored the effects of paracetamol (acetaminophen) ingestion on endurance performance, but their findings are conflicting. Therefore, this review aimed to conduct a meta-analysis examining the effects of paracetamol ingestion on endurance performance. Five databases were searched to find relevant studies. The PEDro checklist was used to assess the methodological quality of the included studies. Data reported in the included studies were pooled in a random-effects meta-analysis. A total of ten studies with good or excellent methodological quality were included in the meta-analysis (pooled n = 141). All included studies had a randomized, double-blind, crossover design. In the main meta-analysis, there was no significant difference between the effects of placebo and paracetamol on endurance performance (Cohen's d = 0.09; 95% confidence interval (CI): -0.04, 0.22; p = 0.172). However, an ergogenic effect was found when we considered only the studies that provided paracetamol 45 to 60 min before exercise (Cohen's d = 0.14; 95% CI: 0.07, 0.21; p < 0.001). In a subgroup analysis that focused on time-to-exhaustion tests, there was a significant ergogenic effect of paracetamol ingestion (Cohen's d = 0.19; 95% CI: 0.06, 0.33; p = 0.006). There was no significant difference between placebo and paracetamol in a subgroup analysis that focused on time trial tests (Cohen's d = 0.05; 95% CI: -0.12, 0.21; p = 0.561). In conclusion, paracetamol ingestion appears to enhance performance (a) in time-to-exhaustion endurance tests and (b) when consumed 45 to 60 min before exercise.

Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance

Exercise causes major shifts in multiple ions (e.g., K⁺ , Na⁺ , H⁺ , lactate^- , Ca²⁺ , and Cl^- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K⁺ , Na⁺ , and Ca²⁺ during fatiguing exercise, while changes in gradients for Cl^- and Cl^- conductance may exert either protective or detrimental effects on fatigue. Myocellular H⁺ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca²⁺ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na⁺ /K⁺ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K⁺ and Cl^- , respectively via metabolic regulation of the ATP-sensitive K⁺ channel (K_ATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.

No additive effect of acetaminophen when co-ingested with caffeine on cycling performance in well-trained young men

We investigated the effect of caffeine and acetaminophen on power output during a 6-min performance test, peripheral fatigue, and muscle protein kinase A (PKA) substrate phosphorylation. Fourteen men [age (means ± SD): 26 ± 6 yr; V̇o_2max: 63.9 ± 5.0 mL·min^-1·kg^-1] completed four randomized trials with acetaminophen (1,500 mg), caffeine (5 mg·kg body wt^-1), combined caffeine and acetaminophen (caffeine + acetaminophen), or placebo. Mean power output during the 6-min performance test (placebo mean: 312 ± 41 W) was higher with caffeine (+5 W; 95% CI: 1 to 9; P = 0.017) and caffeine + acetaminophen (+6 W; 95% CI: 0 to 12; P = 0.049) than placebo, but not with acetaminophen (+1 W; 95% CI: -4 to 7; P = 0.529). Decline in quadriceps maximal isometric voluntary torque immediately after the performance test was lower (treatment × time; P = 0.035) with acetaminophen (-40 N·m; 95% CI: -53 to -30; P < 0.001) and caffeine + acetaminophen (-44 N·m; 95% CI: -58 to -30; P < 0.001) than placebo (-53 N·m; 95% CI: -71 to -39; P < 0.001) but was similar with caffeine (-54 N·m; 95% CI: -69 to -38; P < 0.001). Muscle phosphocreatine content decreased more during the performance test (treatment × time; P = 0.036) with caffeine + acetaminophen (-55 mmol·kg dry wt^-1; 95% CI: -65 to -46; P < 0.001) than placebo (-40 mmol·kg dry wt^-1; 95% CI: -52 to -24; P < 0.001). Muscle net lactate accumulation was not different from placebo (+85 mmol·kg dry wt^-1; 95% CI: 60 to 110; P < 0.001) for any treatment (treatment × time; P = 0.066), being +75 mmol·kg dry wt^-1 (95% CI: 51 to 99; P < 0.001) with caffeine, +76 mmol·kg dry wt^-1 (95% CI: 58 to 96; P < 0.001) with acetaminophen, and +103 mmol·kg dry wt^-1 (95% CI: 89 to 115; P < 0.001) with caffeine + acetaminophen. Decline in muscle ATP and glycogen content and increase in PKA substrate phosphorylation was not different between treatments (treatment × time; P > 0.1). Thus, acetaminophen provides no additive performance enhancing effect to caffeine during 6-min maximal cycling. In addition, change in PKA activity is likely not a major mechanism of performance improvement with caffeine.NEW & NOTEWORTHY Here, we show that acetaminophen does not provide additive performance improvement to caffeine during a 6-min cycling ergometer performance test, and that acetaminophen does not improve performance on its own. Neither substance affects peripheral fatigue, muscle glycolytic energy production, or phosphorylation of muscle proteins of importance for ion handling. In contrast to previous suggestions, increased epinephrine action on muscle cells does not appear to be a major contributor to the performance enhancement with caffeine.

Effects of Ibuprofen during Exertional Heat Stroke in Mice

Intestinal injury is one of the most prominent features of organ damage in exertional heat stroke (EHS). However, whether damage to the intestine in this setting is exacerbated by ibuprofen (IBU), the most commonly used nonsteroidal anti-inflammatory drug in exercising populations, is not well understood.

PURPOSE

We hypothesized that IBU would exacerbate intestinal injury, reduce exercise performance, and increase susceptibility to heat stroke.

METHODS

To test this hypothesis, we administered IBU via diet to male and female C57/BL6J mice, over 48 h before EHS. Susceptibility to EHS was determined by assessing exercise response using a forced running wheel, housed inside an environmental chamber at 37.5°C. Core temperature (Tc) was monitored by telemetry. Mice were allocated into four groups: exercise only (EXC); EHS + IBU; EXC + IBU; and EHS only. Exercise performance and Tc profiles were evaluated and stomachs, intestines and plasma were collected at 3 h post-EHS.

RESULTS

The EHS + IBU males ran approximately 87% longer when Tc was above 41°C (P < 0.03) and attained significantly higher peak Tc (P < 0.01) than EHS-only mice. Histological analyses showed decreased villi surface area throughout the small intestine for both sexes in the EXC + IBU group versus EXC only. Interestingly, though EHS in both sexes caused intestinal injury, in neither sex were there any additional effects of IBU.

CONCLUSIONS

Our results suggest that in a preclinical mouse model of EHS, oral IBU at pharmacologically effective doses does not pose additional risks of heat stroke, does not reduce exercise performance, and does not contribute further to intestinal injury, though this could have been masked by significant gut injury induced by EHS alone.

Acute effects of acetaminophen on the developmental, swimming performance and cardiovascular activities of the African catfish embryos/larvae (Clarias gariepinus)

Acetaminophen is a widely used analgesic that has been detected in many water bodies with few reports concerning its potential toxicity to fish. This study sought to assess the developmental, swimming performance and cardiovascular activities of embryo/larvae catfish (Clarias gariepinus) exposed to acetaminophen. The Organization for Economic Development (OECD) Fish Embryo Acute Toxicity Test (OECD 236) was employed. Fertilized embryo were exposed to different concentrations of acetaminophen (0, 0.5, 1, 10 µg/L) for 96 h. Hatching rates of the embryo were observed to decrease with increasing concentrations of acetaminophen. Fish embryo exposed to acetaminophen displayed varying levels of teratogenic effects at different levels of development in a dose-dependent manner. The results also showed a significant (p < 0.05) dose-dependent increase in swimming speed and movement patterns in fish larvae exposed to acetaminophen, with distance travelled in larvae exposed to the highest concentration of acetaminophen (10 µg/L) about eight (8) times the distance travelled by the control larvae, indicating that acetaminophen-induced erratic swimming behaviour in the catfish species. Cardiotoxicity was evident, with a significant reduction in heartbeat rate with increasing concentrations of acetaminophen. The results showed that exposure to acetaminophen resulted in teratogenic, neurotoxic and cardiotoxic effects in embryo/larvae of Clarias gariepinus. The findings suggest that acetaminophen which has recently been detected in many water bodies could potentially impact on survival of aquatic life, especially catfish.

Images depicting human pain increase exercise-induced pain and impair endurance cycling performance

The current study investigated whether viewing images of others in pain influences exercise-induced pain (EIP) and cycling performance. Twenty-one recreational cyclists attended five laboratory visits. The first two visits involved measuring participants' maximal aerobic capacity and familiarized participants to the fixed power (FP) and 16.1 km cycling time trial (TT) tasks. The FP task required participants to cycle at 70% of their maximal aerobic power for 10-minutes. In the subsequent three visits, participants performed the FP and TT tasks after viewing pleasant, ‎painful or neutral images. Participants rated the subset of painful images as more painful than the pleasant and neutral images; with no difference in the pain ratings of the pleasant and neutral images. In the FP task, EIP ratings were higher following painful compared to pleasant images, while no differences in EIP were observed between any other condition . In the TT, performance did not differ between the pleasant and neutral conditions. However, TT performance was reduced after viewing painful images compared to neutral or pleasant images. HR, B[La], perceived exertion and EIP did not differ between the three conditions. These results suggest that viewing painful images decreases TT performance and increases pain during fixed intensity cycling.‎ Abbreviations: EIP: Exercise Induced Pain; FP: Fixed Power; TT: Time Trial; HR:Heart Rate; B[La]: Blood Lactate; RPE: Rating of Perceived Exertion; IAPS: International Affective Picture System; PO: Power Output.

Centrally-mediated regulation of peripheral fatigue during knee extensor exercise and consequences on the force-duration relationship in older men

The aim of the present study was to investigate the existence of a critical threshold beyond which peripheral fatigue would not further decrease during knee extensor (KE) exercise in older men, and the consequences of this mechanism on the force-duration relationship. Twelve old men (59 ± 2 years) randomly performed two different sessions, in which they performed 60 maximum voluntary contractions (MVC; 3s contraction, 2s relaxation). One trial was performed in the unfatigued state (CTRL) and one other following fatiguing neuromuscular electrical stimulation of the KE (F_NMES). Peripheral and central fatigue were quantified via pre/post-exercise decreases in quadriceps twitch-force (Δ P_tw) and voluntary activation (ΔVA). Critical torque (CT) was determined as the mean force of the last 12 contractions while W' was calculated as the area above CT. Compared with CTRL, pre-fatigue (Δ P_tw= -10.3 ± 6.2%) resulted in a significant (p < 0.05) reduction in W' (-18.2 ± 1.6%) in F_NMES. However, CT (∼964 N), ΔVA (∼15%) and Δ P_tw (∼25%) post-MVCs were similar between both conditions. In CTRL, W' was correlated with Δ P_tw (r ² = 0.78). Moreover, the difference in W' between CTRL and F_NMES was correlated with the level of pre-fatigue induced in F_NMES (r ² = 0.76). These findings document that peripheral fatigue is confined to an individual threshold during KE exercise in older men. Furthermore, correlative results suggest that mechanisms regulating peripheral fatigue to a critical threshold also restrict W', and therefore play a role in exercise capacity in older men.

Contralateral fatigue during severe-intensity single-leg exercise: influence of acute acetaminophen ingestion

Exhaustive single-leg exercise has been suggested to reduce time to task failure (T_lim) during subsequent exercise in the contralateral leg by exacerbating central fatigue development. We investigated the influence of acetaminophen (ACT), an analgesic that may blunt central fatigue development, on T_lim during single-leg exercise completed with and without prior fatiguing exercise of the contralateral leg. Fourteen recreationally active men performed single-leg severe-intensity knee-extensor exercise to T_lim on the left (Leg₁) and right (Leg₂) legs without prior contralateral fatigue and on Leg₂ immediately following Leg₁ (Leg_2-CONTRA). The tests were completed following ingestion of 1-g ACT or maltodextrin [placebo (PL)] capsules. Intramuscular phosphorus-containing metabolites and substrates and muscle activation were assessed using ³¹P-MRS and electromyography, respectively. T_lim was not different between Leg_1ACT and Leg_1PL conditions (402 ± 101 vs. 390 ± 106 s, P = 0.11). There was also no difference in T_lim between Leg_2ACT-CONTRA and Leg_2PL-CONTRA (324 ± 85 vs. 311 ± 92 s, P = 0.10), but T_lim was shorter in Leg_2ACT-CONTRA and Leg_2PL-CONTRA than in Leg_2CON (385 ± 104 s, both P < 0.05). There were no differences in intramuscular phosphorus-containing metabolites and substrates or muscle activation between Leg_1ACT and Leg_1PL and between Leg_2ACT-CONTRA and Leg_2PL-CONTRA (all P > 0.05). These findings suggest that levels of metabolic perturbation and muscle activation at T_lim are not different during single-leg severe-intensity knee-extensor exercise completed with or without prior fatiguing exercise of the contralateral leg. Despite contralateral fatigue, ACT ingestion did not alter neuromuscular responses, muscle metabolites, or exercise performance.

Acetaminophen ingestion improves muscle activation and performance during a 3-min all-out cycling test

Acute acetaminophen (ACT) ingestion has been shown to enhance cycling time-trial performance. The purpose of this study was to assess whether ACT ingestion enhances muscle activation and critical power (CP) during maximal cycling exercise. Sixteen active male participants completed two 3-min all-out tests against a fixed resistance on an electronically braked cycle ergometer 60 min after ingestion of 1 g of ACT or placebo (maltodextrin, PL). CP was estimated as the mean power output over the final 30 s of the test and W′ (the curvature constant of the power–duration relationship) was estimated as the work done above CP. The femoral nerve was stimulated every 30 s to measure membrane excitability (M-wave) and surface electromyography (EMGRMS) was recorded continuously to infer muscle activation. Compared with PL, ACT ingestion increased CP (ACT: 297 ± 32 W vs. PL: 288 ± 31 W, P < 0.001) and total work done (ACT: 66.4 ± 6.5 kJ vs. PL: 65.4 ± 6.4 kJ, P = 0.03) without impacting W′ (ACT: 13.1 ± 2.9 kJ vs. PL: 13.6 ± 2.4 kJ, P = 0.19) or the M-wave amplitude (P = 0.66) during the 3-min all-out cycling test. Normalised EMGRMS amplitude declined throughout the 3-min protocol in both PL and ACT conditions; however, the decline in EMGRMS amplitude was attenuated in the ACT condition, such that the EMGRMS amplitude was greater in ACT compared with PL over the last 60 s of the test (P = 0.04). These findings indicate that acute ACT ingestion might increase performance and CP during maximal cycling exercise by enhancing muscle activation.

Acute ibuprofen ingestion does not attenuate fatigue during maximal intermittent knee extensor or all-out cycling exercise

Recent research suggests that acute consumption of pharmacological analgesics can improve exercise performance, but the ergogenic potential of ibuprofen (IBP) administration is poorly understood. This study tested the hypothesis that IBP administration would enhance maximal exercise performance. In one study, 13 physically active males completed 60 × 3-s maximal voluntary contractions (MVCs) of the knee extensors interspersed with 2-s passive recovery periods, on 2 occasions, with the critical torque (CT) estimated as the mean torque over the last 12 contractions (part A). In another study, 16 active males completed two 3-min all-out tests against a fixed resistance on an electronically braked cycle ergometer, with the critical power estimated from the mean power output over the final 30 s of the test (part B). All tests were completed 60 min after ingestion of maltodextrin (placebo, PL) or 400 mg of IBP. Peripheral nerve stimulation was administered at regular intervals and electromyography was measured throughout. For part A, mean torque (IBP: 60% ± 13% of pre-exercise MVC; PL: 58% ± 14% of pre-exercise MVC) and CT (IBP: 41% ± 16% of pre-exercise MVC; PL: 40% ± 15% of pre-exercise MVC) were not different between conditions (P > 0.05). For part B, end-test power output (IBP: 292 ± 28 W; PL: 288 ± 31 W) and work done (IBP: 65.9 ± 5.9 kJ; PL: 65.4 ± 6.4 kJ) during the 3-min all-out cycling tests were not different between conditions (all P > 0.05). For both studies, neuromuscular fatigue declined at a similar rate in both conditions (P > 0.05). In conclusion, acute ingestion of 400 mg of IBP does not improve single-leg or maximal cycling performance in healthy humans.

Analgesic and anti-inflammatory drugs in sports: Implications for exercise performance and training adaptations

Over-the-counter analgesics, such as anti-inflammatory drugs (NSAIDs) and paracetamol, are widely consumed by athletes worldwide to increase pain tolerance, or dampen pain and reduce inflammation from injuries. Given that these drugs also can modulate tissue protein turnover, it is important to scrutinize the implications of acute and chronic use of these drugs in relation to exercise performance and the development of long-term training adaptations. In this review, we aim to provide an overview of the studies investigating the effects of analgesic drugs on exercise performance and training adaptations relevant for athletic development. There is emerging evidence that paracetamol might acutely improve important endurance parameters as well as aspects of neuromuscular performance, possibly through increased pain tolerance. Both NSAIDs and paracetamol have been demonstrated to inhibit cyclooxygenase (COX) activity, which might explain the reduced anabolic response to acute exercise bouts. Consistent with this, NSAIDs have been reported to interfere with muscle hypertrophy and strength gains in response to chronic resistance training in young individuals. Although it remains to be established whether any of these observations also translate into detriments in sport-specific performance or reduced training adaptations in elite athletes, the extensive use of these drugs certainly raises practical, ethical, and important safety concerns that need to be addressed. Overall, we encourage greater awareness among athletes, coaches, and support staff on the potential adverse effects of these drugs. A risk-benefit analysis and professional guidance are strongly advised before the athlete considers analgesic medicine for training or competition.