vendex and Ischemia

Ischemic conditioning (IC) on the arm or leg has emerged as an intervention to improve strength and performance in healthy populations, but the effects on neurological populations are unknown. The purpose of this study was to quantify the effects of a single session of IC on knee extensor strength and muscle activation in chronic stroke survivors. Maximal knee extensor torque measurements and surface EMG were quantified in 10 chronic stroke survivors (>1 yr poststroke) with hemiparesis before and after a single session of IC or sham on the paretic leg. IC consisted of 5 min of compression with a proximal thigh cuff (inflation pressure = 225 mmHg for IC or 25 mmHg for sham) followed by 5 min of rest. This was repeated five times. Maximal knee extensor strength, EMG magnitude, and motor unit firing behavior were measured before and immediately after IC or sham. IC increased paretic leg strength by 10.6 ± 8.5 Nm, whereas no difference was observed in the sham group (change in sham = 1.3 ± 2.9 Nm, P = 0.001 IC vs. sham). IC-induced increases in strength were accompanied by a 31 ± 15% increase in the magnitude of muscle EMG during maximal contractions and a 5% decrease in motor unit recruitment thresholds during submaximal contractions. Individuals who had the most asymmetry in strength between their paretic and nonparetic legs had the largest increases in strength ( r

Topics: Electromyography; Female; Humans; Ischemia; Knee; Knee Joint; Male; Middle Aged; Muscle Strength; Muscle, Skeletal; Paresis; Pilot Projects; Prospective Studies; Recruitment, Neurophysiological; Single-Blind Method; Stroke; Torque

We sought to determine if blood flow restriction (BFR) by itself or in combination with exercise would result in prolonged decrements in torque when using restriction pressures relative to the participants' limb size. Sixteen participants were randomized into Experiment A (n = 9) or Experiment B (n = 7). Experiment A participants performed unilateral knee extensions at 30 % of their one repetition maximum (1RM) with moderate blood flow restriction on one leg (BFR + Exercise) and exercised the other leg without BFR (CON + Exercise). Experiment B participants rested for 4 min with BFR applied to one leg and rested for 4 min without any treatment on the other leg (CON). Maximal voluntary isometric torque (MVC) was measured before and immediately after the exercise or 4 min of rest, 1 h post, and 24 h post. Ratings of perceived exertion (RPE) and discomfort were taken before and after each set. MVC was significantly reduced following both exercise conditions with BFR + Exercise having the largest reduction in torque. However, torque quickly recovered by 1 h post exercise and was back to baseline by 24 h. No changes in torque were observed in Experiment B. RPE and discomfort were rated consistently higher for those in the BFR + Exercise and BFR conditions compared to control. In conclusion, BFR + Exercise does not result in prolonged decrements in torque. The acute changes in torque are due to fatigue and quickly recover back to baseline within 24 h of exercise. In addition, BFR in the absence of exercise has no effect on torque at any time point.

Topics: Adult; Analysis of Variance; Biomechanical Phenomena; Exercise; Female; Humans; Ischemia; Isometric Contraction; Lower Extremity; Male; Muscle, Skeletal; Perception; Recovery of Function; Regional Blood Flow; Time Factors; Torque; Young Adult

In this investigation we aimed to determine whether: (1) physical activity protects rat skeletal muscle from ischemia/reperfusion (I/R) injury; and (2) continued activity after I/R improves the rate of healing.. Rats were divided into sedentary or active (voluntary wheel running) groups. Active rats ran for 4 weeks before I/R or 4 weeks before plus 4 weeks after I/R.. Activity before I/R resulted in 73.2% less muscle damage (Evans blue dye inclusion). Sedentary and active rats had a similar decline in neural-evoked (∼ 99%) and directly stimulated (∼ 70%) in vivo muscle torque, and a similar reduction in junctophilin 1. Active rats produced 19% and 15% greater neural-evoked torque compared with sedentary rats at 14 and 28 days postinjury, respectively, although the rate of recovery appeared similar.. Activity protects against long-term muscle damage, but not short-term neural injury or excitation-contraction uncoupling. Continued activity neither accelerates nor hinders the rate of functional recovery.

Topics: Animals; Body Weight; Disease Models, Animal; Ischemia; Isometric Contraction; Male; Muscle Fibers, Skeletal; Muscular Diseases; Physical Conditioning, Animal; Rats; Rats, Inbred Lew; Regeneration; Reperfusion Injury; Running; Statistics, Nonparametric; Torque

The aim of this study is to compare values of force-velocity and functional walking capacity in elderly patients with intermittent claudication with respect to the control group.. The study involved 135 individuals: 85-peripheral arterial disease (PAD) group diagnosed with stage II chronic lower limb ischemia, according to Fontaine's classification, and 50-control group. The studies included an assessment of walking capacity using a six-minute walk test (6MWT) and measurement of force-velocity parameters (peak torque-PTQ, total work-TW, average power-AVGP) of the lower limbs obtained by means of a functional dynamometry under isokinetic conditions.. The peripheral arterial disease group is characterized by significantly lower values of force-velocity parameters compared to the control group (p<0.005). Walking capacity in this group is significantly reduced due to significant differences in the distance covered (p<0.0001), walking speed (p<0.01), and its intensity (p<0.01). Further, a positive correlation was found between the maximum distance specified in the six-minute walk test and lower limb muscle strength in the isokinetic test.. Mean values of all force-velocity parameters and walk distance were significantly higher in the control group than in the peripheral arterial disease group. In the PAD group, in both men and women, the value of the agonist/antagonist ratio of both lower limbs are lower in men and women comparing to the control group. A rehabilitation program for patients with intermittent claudication must consider exercises improving strength, exercise capacity, and endurance in patients with PAD.

Topics: Aged; Exercise Test; Female; Humans; Intermittent Claudication; Ischemia; Lower Extremity; Male; Middle Aged; Muscle Strength; Muscle, Skeletal; Peripheral Arterial Disease; Torque; Walking

During muscle fatigue, firing of small-diameter muscle afferents can decrease voluntary activation of the fatigued muscle. However, these afferents may have a more widespread effect on other muscles in the exercising limb. We examined if the firing of fatigue-sensitive afferents from elbow extensor muscles in the same arm reduces torque production and voluntary activation of elbow flexors. In nine subjects we examined voluntary activation of elbow flexors by measuring changes in superimposed twitches evoked by transcranial magnetic stimulation of the motor cortex during brief (2-3 s) maximal voluntary contractions (MVC). Inflation of a blood pressure cuff following a 2-min sustained MVC blocked blood flow to the fatigued muscle and maintained firing of small-diameter afferents. After a fatiguing elbow flexion contraction, maximal flexion torque was lower (26.0 ± 4.4% versus 67.9 ± 5.2% of initial maximal torque; means ± s.d.; P < 0.001) and superimposed twitches were larger (4.1 ± 1.1% versus 1.8 ± 0.2% ongoing MVC, P = 0.01) with than without ischaemia. After a fatiguing elbow extensor contraction, maximal flexion torque was also reduced (82.2 ± 4.9% versus 91.4 ± 2.3% of initial maximal torque; P = 0.007), superimposed twitches were larger (2.7 ± 0.7% versus 1.3 ± 0.2% ongoing MVC; P = 0.02) and voluntary activation lower (81.6 ± 8.2% versus 95.5 ± 6.9%; P = 0.04) with than without ischaemia. After a fatiguing contraction, voluntary drive to the fatigued muscles is reduced with continued input from small-diameter muscle afferents. Furthermore, fatigue of the elbow extensor muscles decreases voluntary drive to unfatigued elbow flexors of the same arm. Therefore, firing of small-diameter muscle afferents from one muscle can affect voluntary activation and hence torque generation of another muscle in the same limb.

Topics: Adult; Elbow; Electric Stimulation; Female; Humans; Ischemia; Male; Middle Aged; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Torque; Transcranial Magnetic Stimulation; Young Adult

The aim of this study was to investigate the relative contribution of human muscle reoxygenation on force recovery following a maximal voluntary contraction (MVC). Ten athletes (22·9 ± 4·0 years) executed a plantar-flexion sequence including two repeated MVCs [i.e. a 30-s MVC (MVC(30)) followed by a 10-s MVC (MVC(10))] separated by 10, 30, 60, 120 or 300 s of passive recovery. A 10-min passive recovery period was allowed between each MVC sequence. This procedure was randomly repeated with two different recovery conditions: without (CON) or with (OCC) arterial occlusion of the medial gastrocnemius. During OCC, the occlusion was maintained from the end of MVC(30) to the end of MVC(10). Muscle oxygenation (Near-infrared spectroscopy, NIRS, [Hb(diff) ]) was continuously measured during all MVC sequences and expressed as a percentage of the maximal changes in optical density observed during MVC(30). Maximal Torque was analysed at the start of each contraction. Torque during each MVC(10) was expressed as a percentage of the Torque during the previous MVC(30). Torque recovery was complete within 300 s after MVC(30) during CON (MVC(10) = 101·8 ± 5·0%); 88·6 ± 8·9% of the Torque was recovered during OCC (P = 0·005). There was also a moderate correlation between absolute level of muscle oxygenation and Torque (r = 0·32 (90% CI, 0·09;0·52), P = 0·02). Present findings confirm the role of human muscle oxygenation in muscular force recovery during repeated-maximal efforts. However, the correlation between absolute muscle oxygenation and force level during recovery is only moderate, suggesting that other mechanisms are likely involved in the force recovery process.

Topics: Adult; Analysis of Variance; Biomechanical Phenomena; Humans; Ischemia; Male; Muscle Contraction; Muscle Strength; Muscle, Skeletal; Oxygen; Oxygen Consumption; Qatar; Recovery of Function; Regional Blood Flow; Spectroscopy, Near-Infrared; Time Factors; Torque; Tourniquets; Young Adult

Changes in muscle excitability were investigated during fatigue and the recovery of human dorsi- and plantar-flexor isometric contractions. The indirectly evoked muscle compound action potentials [tibialis anterior (TA) and soleus (SOL) M-waves] were used as an index of excitability. Ten subjects successfully completed five experiments, spaced at least 1 week apart, in which intermittent tetanic trains at different frequencies of stimulation (0-30 Hz) were used to fatigue the ankle dorsi-flexors. Muscles were rendered ischaemic via a thigh cuff inflated above mean arterial pressure. The effects of ischaemia were examined by repeating the 20-Hz stimulation protocol under non-ischaemic conditions. Five of those subjects also participated in one further session in which the ischaemic plantar-flexors were also fatigued. It was hypothesized that muscle excitability would be preferentially retained in the SOL. Maintenance of excitability in both muscles was possible for 1 min regardless of stimulus frequency; thereafter, stimulation at the highest frequencies induced the greatest decline [30 Hz stimulation; 95.4 (0.5)%, P < 0.01) in the amplitude of the M-wave. The decline in M-wave amplitude was always greater than the decline in M-wave area and occurred at firing rates not normally associated with neuromuscular blockade, implying propagation failure along the sarcolemma. The presence of ischaemia significantly accelerated the decline in both amplitude (78% versus 12%, P<0.01) and area (45% versus no decline, P<0.01) of the M-wave. Recovery was limited when tetanic stimulation ceased but progressed rapidly after circulation was restored. Twitch and tetanic torque declines were significantly different between SOL and TA (fall between rest and fatigue -SOL: 77%, 75.2%; TA: 95.5%, 96.9%, P<0.01, respectively). M-wave changes between the two muscles were not significantly different although the onset of the decline was delayed in the SOL. It is proposed that the observed delay in fatiguing decline was due to the early potentiation in muscle excitability observed in the SOL but not in the TA.

Topics: Action Potentials; Adult; Ankle Joint; Electric Stimulation; Electromyography; Female; Humans; Ischemia; Isometric Contraction; Male; Muscle Fatigue; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Recovery of Function; Sarcolemma; Torque

Variations in the levels of muscle hemoglobin and of myoglobin oxygen saturation can be detected non-invasively with near-infrared spectroscopy. This technique could be applied to the diagnosis of chronic compartment syndrome, in which invasive testing has shown increased intramuscular pressure associated with ischemia and pain during exercise. We simulated chronic compartment syndrome in ten healthy subjects (seven men and three women) by applying external compression, through a wide inflatable cuff, to increase the intramuscular pressure in the anterior compartment of the leg. The tissue oxygenation of the tibialis anterior muscle was measured with near-infrared spectroscopy during gradual inflation of the cuff to a pressure of forty millimeters of mercury (5.33 kilopascals) during fourteen minutes of cyclic isokinetic dorsiflexion and plantar flexion of the ankle. The subjects exercised with and without external compression. The data on tissue oxygenation for each subject then were normalized to a scale of 100 per cent (the baseline value, or the value at rest) to 0 per cent (the physiological minimum, or the level of oxygenation achieved by exercise to exhaustion during arterial occlusion of the lower extremity). With external compression, tissue oxygenation declined at a rate of 1.4 +/- 0.3 per cent per minute (mean and standard error) during exercise. After an initial decrease at the onset, tissue oxygenation did not decline during exercise without compression. The recovery of tissue oxygenation after exercise was twice as slow with compression (2.5 +/- 0.6 minutes) than it was without the use of compression (1.3 +/- 0.2 minutes).

Topics: Adolescent; Adult; Chronic Disease; Compartment Syndromes; Female; Hemoglobins; Humans; Ischemia; Isometric Contraction; Leg; Male; Middle Aged; Monitoring, Physiologic; Muscle Contraction; Muscle, Skeletal; Myoglobin; Oxygen Consumption; Pain; Physical Endurance; Physical Exertion; Pressure; Spectroscopy, Near-Infrared; Torque