Paraspinal muscle oxygenation and mechanical efficiency are reduced in individuals with chronic low back pain.

This study aimed to compare the systemic and local metabolic responses during a 5-min trunk extension exercise in individuals with chronic low back pain (CLBP) and in healthy individuals. Thirteen active participants with CLBP paired with 13 healthy participants performed a standardised 5-min trunk extension exercise on an isokinetic dynamometer set in continuous passive motion mode. During exercise, we used near-infrared spectroscopy to measure tissue oxygenation (TOI) and total haemoglobin-myoglobin (THb). We used a gas exchange analyser to measure breath-by-breath oxygen consumption (V̇O2) and carbon dioxide produced (V̇CO2). We also calculated mechanical efficiency. We assessed the intensity of low back pain sensation before and after exercise by using a visual analogue scale. In participants with CLBP, low back pain increased following exercise (+ 1.5 units; p < 0.001) and THb decreased during exercise (- 4.0 units; p = 0.043). Paraspinal muscle oxygenation (65.0 and 71.0%, respectively; p = 0.009) and mechanical efficiency (4.7 and 5.3%, respectively; p = 0.034) were both lower in participants with CLBP compared with healthy participants. The increase in pain sensation was related to the decrease in tissue oxygenation (R2 = - 0.420; p = 0.036). Decreases in total haemoglobin-myoglobin and mechanical efficiency could involve fatigability in exercise-soliciting paraspinal muscles and, therefore, exacerbate inabilities in daily life. Given the positive correlation between tissue oxygenation and exercise-induced pain exacerbation, muscle oxygenation may be related to persisting and crippling low back pain.

Neural Drive Impairment in Chronic Kidney Disease Patients Is Associated with Neuromuscular Fatigability and Fatigue.

INTRODUCTION: Chronic kidney disease (CKD) patients have a high degree of fatigue relating to neuromuscular symptoms. There is a lack of evidence regarding the etiology of neuromuscular fatigability in elderly CKD patients. METHODS: Inclusion criteria are as follows: age ≥60 yr, glomerular filtration rate (GFR) <45 mL·min -1 per 1.73 m 2 in CKD patients, and GFR >60 mL·min -1 ·1.73 m -2 in controls. The fatigability protocol consisted in a submaximal handgrip task at 40% peak force. Fatigue was assessed using the Multidimensional Fatigue Inventory-20 items (MFI-20) and the Functional Assessment of Chronic Illness Therapy-Fatigue questionnaires. Peak rate of force development (RFD peak , normalized: NRFD peak ) and rate of EMG rise (RER) were measured during explosive contractions; peak force and mean surface EMG were measured during maximum voluntary contractions. Multilevel models tested neuromuscular parameters adjusted for clinical and Multidimensional Fatigue Inventory-20 items subscales. Neuromuscular fatigability contribution to fatigue description was tested using model comparison. RESULTS: The study included 102 participants; 45 CKD patients and 57 controls. CKD mainly affected the mental and the reduced motivation subscales of fatigue. CKD was associated with greater neuromuscular fatigability assessed using NRFD peak (group-time interaction, -16.7 % MVF·s -1 , P = 0.024), which increased with fatigue severity ( P = 0.018) and with a higher rate of decrement in RER compared with controls (RER at 50 ms: ß = -121.2 µV·s -1 , P = 0.016, and ß = -48.5 µV·s -1 , P = 0.196, respectively). Furthermore, these patients show an association between the reduced motivation subscale and the RER (e.g., 30 ms: ß = -59.8% EMG peak ·s -1 , P < 0.001). Only peak force fatigability contributed to fatigue variance, whereas RFD peak did not. CONCLUSIONS: In CKD patients, the neuromuscular fatigability assessed using RFD peak is related to an impairment in motor-unit recruitment or discharge rates, whereas only peak force fatigability was related to fatigue. This suggests that targeting exercise interventions might lessen fatigue and improve quality of life in CKD patients.

Benefits of a four-week functional restoration program in chronic low back pain patients and three-month follow-up: focus on paraspinal muscle aerobic metabolism responses to exercise.

BACKGROUND: Chronic low back pain (CLBP) is a major health concern characterized by paraspinal muscle fatigability. This can be improved following a functional restoration program. Muscle fatigability can be related to impairment in aerobic metabolism responses. In this study, we investigated paraspinal muscles aerobic metabolism in CLBP patients before and after a functional restoration program, in order to determine if the enhancement in patients' condition following the program is associated to changes in metabolism responses. METHODS: Twenty-two CLBP patients (11 women, 11 men; 41.6±1.8 years; 73.7±3.1 kg; 1.74±0.02 m) were evaluated before and after a 4-week functional restoration program, with exercise therapy as the main component. Three months later, 12 patients were seen for a follow-up visit. During each testing session, patients performed a five-minute isokinetic trunk extension exercise in measuring pulmonary gas exchanges and paraspinal muscle oxygenation. Mechanical efficiency and onset V̇O2 kinetics were also calculated, in addition to usual questionnaires and exercises designed to evaluate psychosocial and physical factors. RESULTS: At the end of the program, paraspinal muscle oxygenation, mechanical efficiency, and the V̇O2 onset kinetics were improved (P<0.05). All measures remained stable during the three-month follow-up except for paraspinal muscle oxygenation, which deteriorated (P<0.05). Return-to-work was associated with the level of workday physical activities and to a decrease in fear-avoidance beliefs. CONCLUSIONS: At the end of the program, aerobic metabolism responses were improved in paraspinal muscles in patients. These improvements were not associated with return-to-work, which was primarily influenced by socio-psychological factors.

Trunk Muscle Aerobic Metabolism Responses in Endurance Athletes, Combat Athletes and Untrained Men.

This study investigated aerobic metabolism responses in trunk muscles during a prolonged trunk extension exercise in athletes and untrained young men. The aim was to analyze the adaptations induced by 2 types of sports: one involving intensive use of trunk muscles (i. e., judo), and one known to induce high aerobic capacity in the whole body (i. e., cycling). Eleven judokas, 10 cyclists and 9 healthy untrained young men performed trunk extension exercises on an isokinetic dynamometer. During the first session, muscle strength was assessed during maximal trunk extension. During a second session, a 5-min exercise was performed to investigate aerobic responses with regard to trunk muscles. The near infrared spectroscopy technique and a gas exchange analyzer were used continuously to evaluate mechanical efficiency, V̇O2 on-set kinetics, trunk muscle deoxygenation and blood volume. Judokas showed greater trunk strength and mechanical efficiency (p<0.05). Cyclists presented faster V̇O2 on-set kinetics (p<0.05) and greater muscle deoxygenation and blood volume compared to untrained men (p<0.001). These results suggest that practicing judo improves trunk extension efficiency whereas cycling accelerates aerobic pathways and enhances microvascular responses to trunk extension exercise. Sport practice improves aerobic metabolism responses in trunk extensor muscles differently, according to the training specificities.

Acute effects of repeated cycling sprints in hypoxia induced by voluntary hypoventilation.

PURPOSE: This study aimed to investigate the acute responses to repeated-sprint exercise (RSE) in hypoxia induced by voluntary hypoventilation at low lung volume (VHL). METHODS: Nine well-trained subjects performed two sets of eight 6-s sprints on a cycle ergometer followed by 24 s of inactive recovery. RSE was randomly carried out either with normal breathing (RSN) or with VHL (RSH-VHL). Peak (PPO) and mean power output (MPO) of each sprint were measured. Arterial oxygen saturation, heart rate (HR), gas exchange and muscle concentrations of oxy-([O2Hb]) and deoxyhaemoglobin/myoglobin ([HHb]) were continuously recorded throughout exercise. Blood lactate concentration ([La]) was measured at the end of the first (S1) and second set (S2). RESULTS: There was no difference in PPO and MPO between conditions in all sprints. Arterial oxygen saturation (87.7 ± 3.6 vs 96.9 ± 1.8% at the last sprint) and HR were lower in RSH-VHL than in RSN during most part of exercise. The changes in [O2Hb] and [HHb] were greater in RSH-VHL at S2. Oxygen uptake was significantly higher in RSH-VHL than in RSN during the recovery periods following sprints at S2 (3.02 ± 0.4 vs 2.67 ± 0.5 L min-1 on average) whereas [La] was lower in RSH-VHL at the end of exercise (10.3 ± 2.9 vs 13.8 ± 3.5 mmol.L-1; p < 0.01). CONCLUSIONS: This study shows that performing RSE with VHL led to larger arterial and muscle deoxygenation than with normal breathing while maintaining similar power output. This kind of exercise may be worth using for performing repeated sprint training in hypoxia.