Muscle pain induced by hypertonic saline in the knee extensors decreases single-limb isometric time to task failure

Purpose: Increased nociceptive activity and the experience of exercise-induced pain (EIP) may contribute to fatigue during endurance exercise. To investigate this, a pain model that produces pain similar to EIP and decouples its’ relationship to exercise intensity is required. This study 1) compared the quality of pain caused by a hypertonic saline injection into the vastus lateralis in resting and exercise conditions, and 2) investigated whether this pain contributes to changes in time to task failure. Methods: On separate days, eighteen participants completed a time to task failure at 20% maximal voluntary torque (MVT), a resting hypertonic saline intramuscular injection, and in a further three visits a time to task failure at 10% MVT following injection of isotonic saline, hypertonic saline or a control (no injection). Results: In a subset of eligible participants (n = 12), the hypertonic saline combined with 10% MVT produced a qualitative experience of pain (assessed by the McGill Pain Questionnaire) that felt similar to EIP. 10% MVT with hypertonic saline significantly elevated pain intensity in the first 20% of the time to task failure and caused a significantly (P < 0.05) shorter time to task failure (448 ± 240 s) compared with the isotonic saline (605 ± 285 s) and control (514 ± 197 s) conditions. Conclusion: These findings demonstrate that hypertonic saline increases the intensity of pain during exercise, which results in a faster occurrence of exercise-induced fatigue. These results provide important evidence supporting pain as a limiting factor in endurance performance

Neuromuscular and perceptual mechanisms of fatigue accompanying task failure in response to moderate-, heavy-, severe-, and extreme-intensity cycling

A comprehensive characterization of neuromuscular and perceptual mechanisms of fatigue at task failure following exercise across the entire intensity spectrum is lacking. This study evaluated the extent of peripheral and central fatigue, and corresponding perceptual attributes, at task failure following cycling within the moderate-(MOD), heavy-(HVY), severe-(SVR), and extreme-(EXT) intensity domains. After a ramp-incremental test, 11 young males performed four constant-power output trials to the limit of tolerance (Tlim) at 4 distinct domain-specific workloads. These trials were preceded and followed by 5-s knee-extension maximal voluntary contractions (MVCs) and femoral nerve electrical stimuli to quantify peripheral and central fatigue. In addition, perceptual measures including ratings of global fatigue, legs pain, dyspnea, and perceived effort (RPE) were also collected. At Tlim, reductions in MVC were independent of intensity (P > 0.05). However, peripheral fatigue was greater following EXT and SVR and progressively, but distinctively, lower following HVY and MOD (P < 0.05). Central fatigue was similar after SVR, HVY, and MOD, but absent after EXT (P < 0.05). At Tlim, subjective ratings of global fatigue were progressively higher with lower exercise intensities, whereas ratings of legs pain and dyspnea were progressively higher with higher exercise intensities. On the other hand, RPE was maximal following HVY, SVR, and EXT, but not MOD. The findings demonstrate that at Tlim, the extent of peripheral fatigue is highly domain-specific, whereas the extent of central fatigue is not. Sensations such as fatigue, pain, and dyspnea may integrate with mechanisms of sense of effort to determine task failure in a manner specific to each intensity domain

Exercising muscle mass influences neuromuscular, cardiorespiratory, and perceptual responses during and following ramp-incremental cycling to task failure

Neuromuscular (NM), cardiorespiratory, and perceptual responses to maximal-graded exercise using different amounts of active muscle mass remain unclear. We hypothesized that during dynamic exercise, peripheral NM fatigue (declined twitch force) and muscle pain would be greater using smaller muscle mass, whereas central fatigue (declined voluntary activation) and ventilatory variables would be greater using larger muscle mass. Twelve males (29.8 ± 4.7 years) performed two ramp-incremental cycling tests until task failure: 1) single-leg (SL) with 10 W·min−1 ramp and 2) double-leg (DL) with 20 W·min−1 ramp. NM fatigue was assessed at baseline, task failure (post), and after 1, 4, and 8 min of recovery. Cardiorespiratory and perceptual variables [i.e., ratings of perceived exertion (RPE), pain, and dyspnea] were measured throughout cycling. Exercise duration was similar between sessions (SL: 857.7 ± 263.6 s; DL: 855.0 ± 218.8 s; P = 0.923), and higher absolute peak power output was attained in DL (SL: 163.2 ± 43.8 W; DL: 307.0 ± 72.0 W; P < 0.001). Although central fatigue did not differ between conditions (SL: −6.6 ± 6.5%; DL: −3.5 ± 4.8%; P = 0.091), maximal voluntary contraction (SL: −41.6 ± 10.9%; DL: −33.7 ± 8.5%; P = 0.032) and single twitch forces (SL: −59.4 ± 18.8%; DL: −46.2 ± 16.2%; P = 0.003) declined more following SL. DL elicited higher peak oxygen uptake (SL: 42.1 ± 10.0 mL·kg−1·min−1; DL: 50.3 ± 9.3 mL·kg−1·min−1; P < 0.001), ventilation (SL: 137.1 ± 38.1 L·min−1; DL: 171.5 ± 33.2 L·min−1; P < 0.001), and heart rate (SL: 167 ± 21 bpm; DL: 187 ± 8 bpm; P = 0.005). Dyspnea (P = 0.025) was higher in DL; however, RPE (P = 0.005) and pain (P < 0.001) were higher in SL. These results suggest that interplay between NM, cardiorespiratory, and perceptual determinants of exercise performance during ramp-incremental cycling to task failure is muscle mass dependent

Effects of pre-induced fatigue vs concurrent pain on exercise tolerance, neuromuscular performance, and corticospinal responses of locomotor muscles

Individuals often need to maintain voluntary contractions during high intensity exercise in the presence of fatigue and pain. This investigation examined the effects of pre-induced fatigue and concurrent rising pain (evoked by muscle ischaemia) in one leg on motor fatigability and corticospinal excitability/inhibition of the contralateral limb. Twelve healthy males undertook four experimental protocols including unilateral cycling to task failure at 80% of peak power output with: (i) the right-leg (RL); (ii) the left-leg (LL); (iii) RL immediately preceded by LL protocol (FAT-RL); and (iv) RL when blood flow was occluded in the contralateral (left) leg (PAIN-RL). Participants performed maximal and submaximal 5 s right-leg knee extensions during which transcranial magnetic and femoral nerve electrical stimuli were delivered to elicit motor-evoked and compound muscle action potentials, respectively. The pre-induced fatigue reduced the right leg cycling time-to-task failure (mean ± SD; 332 ± 137 s) to a greater extent than concurrent pain (460 ± 158 s), compared to RL (580 ± 226 s) (P < 0.001). The maximum voluntary contraction force declined less following FAT-RL (P < 0.019) and PAIN-RL (P < 0.032) compared to RL. Voluntary activation declined and the corticospinal excitability recorded from knee extensors increased similarly after the three conditions (P < 0.05). However, the pre-induced fatigue, but not concurrent pain, reduced corticospinal inhibition compared to RL (P < 0.05). These findings suggest that regardless of the origin and/or mechanisms modulating sensory afferent feedback during single-leg cycling (e.g. pre-induced fatigue vs. concurrent rising pain), the limit of exercise tolerance remains the same, suggesting that exercise will be terminated upon achievement of sensory tolerance limit

Time course of performance fatigability during exercise below, at, and above the critical intensity in females and males

Purpose: This study aimed to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF). Methods: Ten females and 11 males were evaluated in eight visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; and 4-8) cycling to TTF at PO relative to the MLSS of (i) -15%, (ii) -10 W, (iii) at MLSS, and (iv) +10 W, and (v) +15%. Performance fatigability was characterized by femoral nerve electrical stimulation of knee extensors at baseline; minutes 5, 10, 20, and 30; and TTF. Oxygen uptake, blood lactate concentration, muscle oxygen saturation, and perceived exertion were evaluated. Results: Approximately 75% of the total performance fatigability occurred within 5 min of exercise, independently of exercise intensity, followed by a further change at minute 30. Contractile function declined more in males than females (all P < 0.05). At task failure, exercise duration declined from MLSS -15% to MLSS +15% (all P < 0.05), accompanied by a greater rate of decline after MLSS +15% and MLSS +10 compared with MLSS, MLSS -10 , and MLSS -15% for voluntary activation (-0.005 and -0.003 vs -0.002, -0.001 and -0.001%·min -1 , respectively) and contractile function (potentiated single twitch force, -0.013 and -0.009 vs -0.006, -0.004 and -0.004%·min -1 , respectively). Conclusions: Whereas the time course of performance fatigability responses was similar regardless of exercise intensity and sex, the total amplitude and rate of change were affected by the distinct metabolic disturbances around the MLSS, leading to different performance fatigability etiologies at task failure

Preventive Chair Massage With Algometry to Maintain Psychosomatic Balance in White-collar Workers

People working at computers often suffer from overload-related muscle pain, and physical and mental discomfort. The aim of the study was to evaluate the effectiveness of chair massage, conducted in the workplace among white-collar workers, in relieving symptoms of musculoskeletal strain related to prolonged sitting posture. The study was conducted in 124 white-collar workers, 55 women and 69 men, aged 33.7 +/- 7.6 years. Subjects were randomly assigned to three groups: chair massage program, relaxing music sessions, and a control group, each of four-week duration. Each group was evaluated before and after the program completion. Pain perception was assessed algometrically as a threshold for compression pain of neck muscles, measured in kg/cm(2). The relaxation level was assessed from the heart rate variability. We found that the chair massage increased both the pain threshold in all tested muscles (p \u3c 0.001) and the relaxation level from 31.9% to 41.6% (p \u3c 0.05). In the group with music sessions, muscle pain threshold remained unchanged, except for the trapezoid muscle where it decreased (p \u3c 0.05), while the relaxation level increased from 26.0% to 33.3% (p \u3c 0.05). In both massage and relaxing music groups, there was a significant decrease in muscle tension (p \u3c 0.01). Changes in the control group were inappreciable. We conclude that the chair massage performed in the workplace is an effective method for prevention of musculoskeletal overstrain related to prolonged sitting posture. The program seems worth implementing in various occupational environments