Significance of skin temperature changes in surface electromyography

Summary Differing results have been reported concerning the direction and quantity of the electromyogram (EMG) amplitude response to changes in tissue temperature. The EMG signals from the soleus muscle of six healthy human subjects were therefore recorded during dynamic exercise (concentric contractions) at ambient temperatures of 30°C and 14°C. The mean skin temperature above the muscle investigated was 32.9° C and 21.7° C, respectively. The core temperature, estimated by rectal temperature, was unchanged. The cooling of the superficial tissues caused approximately a doubling of the EMG amplitude. For the probability level 0.9 in the amplitude probability distribution function, the average signal level increased from 73 V to 135 V (P=0.02). The average mean power frequency of the EMG signal was reduced from 142 Hz to 83 Hz (P=0.004). The amplitude increase was not due to shivering but other possible explanations are presented. As the changes in T _sk investigated were within the range which may occur normally during the working hours, it was concluded that T _sk should be carefully controlled in vocational EMG studies.     

Increase in the ratio of serum levels of apolipoproteins A-I and A-II during prolonged physical strain and calorie deficiency

Summary Effects of four days of intense physical activity on serum concentrations of total triglycerides, total cholesterol and apolipoproteins A-I, A-II, and B were studied in 35 well-trained young men. Serum total triglyceride levels decreased to 70% of baseline levels after 24 h, and fell further to 50% of baseline levels after 4 days. Serum levels of total cholesterol fell steadily to about 80% of baseline levels on the 4th day. Apo-B levels fell to 85% of baseline levels after 24 h, and remained at that level. Apo A-I fell to about 90%, and apo A-II to about 80% of baseline levels, causing a significant increase in the ratio of apo A-I to apo A-II. The intraindividual changes in apo B were positively correlated to changes in cholesterol during the first day (r=0.60). The changes in apo A-I and apo A-II had no significant correlation with changes in total cholesterol or triglycerides, or with one another, suggesting that apo A-I and apo A-II are metabolized independently during conditions of hard physical exercise.     

The effect on immunity of long-term intensive training in elite swimmers

The impact of long-term training on systemic and mucosal immunity was assessed prospectively in a cohort of elite swimmers over a 7-month training season in preparation for national championships. The results indicated significant suppression (P < 0.05) of serum IgA. IgG and IgM and salivary IgA concentration in athletes associated with long-term training at an intensive level. There was also a trend towards lower IgG2 subclass levels in serum in athletes compared with controls (P= 0.07). There were no significant changes in numbers or percentages of B or T cell subsets, but there was a significant fall in natural killer (NK) cell numbers and percentages in athletes over the training season (P < 0.05). After individual training sessions there was a significant decrease in salivary IgA levels for athletes compared with controls (P= 0.02). In athletes there was a downward trend in salivary IgA levels over the 7-month training period in both the pre-exercise (P= 0.06) and post-exercise samples (P= 0.04). There were no significant trends in salivary IgG levels over the study period in either athletes or controls. The only significant change in salivary IgM levels was an increase in detection rate in the pre-competition phase in athletes (P= 0.03). The study suggests that training of elite athletes at an intensive level over both short- and long-time frames suppresses both systemic and mucosal immunity. Protracted immune suppression linked with prolonged training may determine susceptibility to infection, particularly at times of major competitions.     

Beta-adrenergic blockade and training in healthy men—effects on central circulation

The effect of chronic β-adrenergic blockade on central circulatory adaptations to physical training was investigated. 16 healthy sedentary males (20–31 yrs) trained on cycle ergometers 40 min/day, 4 days a week for 8 weeks at a work load that during the last 5 weeks corresponded to 75% of the pretraining VO₂ max. In a single blind way, 8 subjects were during the training period treated with the β-adrenergic receptor blocker propranolol (160 mg/day), while the remaining 8 received placebo tablets. Pretraining tests were performed before the start of medication and posttraining tests were performed 6 days after the last day of training and medication. The training program resulted in a similar increase (8%) in VO₂ max in both groups (p<0.01). The resting heart rate (-4 beats/min; p<0.05) as well as the exercise heart rate at a moderate work load (120 W: -11 beats/min; p<0.01) decreased with training, and no significant difference was seen between the 2 groups. At a high work load (180 W), however, the heart rate decreased significantly more with training in the placebo group as compared with the β-blockade group (-19 vs.-7 beats/min; p<0.05). The oxygen pulse (VO₂/HR) increased in both groups at 120 W (+6%; p<0.01). At 180 W the oxygen pulse increased only in the placebo group (+8%; p<0.05). The estimated stroke volume at 120 and 180 W, as determined by impedance cardiography, did not change significantly with training although there was a tendency towards an increase in the placebo group only. The resting left ventricular wall thickness and diameter, as determined by echocardiography, did not change significantly with training in either group.—In conclusion, the present study indicates that a moderate degree of β-adrenergic blockade does not prevent or impair the training-induced increase in the maximal oxygen uptake. During submaximal work, however, the circulatory adaptation may be less apparent if training has been performed during partial blockade of the sympathoadrenal system.     

Middle cerebral artery blood velocity depends on cardiac output during exercise with a large muscle mass

We tested the hypothesis that pharmacological reduction of the increase in cardiac output during dynamic exercise with a large muscle mass would influence the cerebral blood velocity/perfusion. We studied the relationship between changes in cerebral blood velocity (transcranial Doppler), rectus femoris blood oxygenation (near-infrared spectroscopy) and systemic blood flow (cardiac output from model flow analysis of the arterial pressure wave) as induced by dynamic exercise of large (cycling) vs. small muscle groups (rhythmic handgrip) before and after cardioselective β₁ adrenergic blockade (0.15 mg kg^?1 metoprolol i.v.). During rhythmic handgrip, the increments in systemic haemodynamic variables as in middle cerebral artery mean blood velocity were not influenced significantly by metoprolol. In contrast, during cycling (e.g. 113 W), metoprolol reduced the increase in cardiac output (222 ± 13 vs. 260 ± 16%), heart rate (114 ± 3 vs. 135 ± 7 beats min^?1) and mean arterial pressure (103 ± 3 vs.112 ± 4 mmHg), and the increase in cerebral artery mean blood velocity also became lower (from 59 ± 3 to 66 ± 3 vs. 60 ± 2 to 72 ± 3 cm s^?1; P < 0.05). Likewise, during cycling with metoprolol, oxyhaemoglobin in the rectus femoris muscle became reduced (compared to rest; ?4.8 ± 1.8 vs. 1.2 ± 1.7 μmol L^?1, P < 0.05). Neither during rhythmic handgrip nor during cycling was the arterial carbon dioxide tension affected significantly by metoprolol. The results suggest that as for the muscle blood flow, the cerebral circulation is also affected by a reduced cardiac output during exercise with a large muscle mass.     

Human temperature regulation during cycling with moderate leg ischaemia

The effect of graded ischaemia in the legs on the regulation of body temperature during steady-state exercise was investigated in seven healthy males. It was hypothesised that graded ischaemia in the working muscles increases heat storage within the muscles, which in turn potentiates sweat secretion during exercise. Blood perfusion in the working muscles was reduced by applying a supra-atmospheric pressure (+6.6 kPa) around the legs, which reduced maximal working capacity by 29%. Each subject conducted three separate test trials comprising 30 min of steady-state cycling in a supine position. Exercise with unrestricted blood flow (Control trial) was compared to ischaemic exercise conducted at an identical relative work rate (Relative trial), as well as at an identical absolute work rate (Absolute trial); the latter corresponding to a 20% increase in relative workload. The average (SD) increases in both the rectal and oesophageal temperatures during steady-state cycling was 0.3 (0.2)°C and did not significantly differ between the three trials. The increase in muscle temperature was similar in the Control (2.7 (0.3)°C) and Absolute (2.4 (0.7)°C) trials, but was substantially lower (P<0.01) in the Relative trial (1.4 (0.8)°C). Ischaemia potentiated (P<0.01) sweating on the forehead in the Absolute trial (24.2 (7.3) g m^–2 min^–1) compared to the Control trial (13.4 (6.2) g m^–2 min^–1), concomitant with an attenuated (P<0.05) vasodilatation in the skin during exercise. It is concluded that graded ischaemia in working muscles potentiates the exercise sweating response and attenuates vasodilatation in the skin initiated by increased core temperature, effects which may be attributed to an augmented muscle metaboreflex.     

Effect of prolonged physical exercise on the fibrinolytic system

Summary The effect of a test marathon race on plasma fibrinolytic activity (FA) was studied in 16 endurance athletes before, immediately after, 3 h, and 31 h after the run. Tissue plasminogen activator (t-PA) activity increased about 31-fold immediately after the run. Similar increases were found in t-PA antigen concentration. Plasminogen activator inhibitor (PAI) was not detectable immediately after the race and was significantly decreased 3 h (P < 0.05) and 31 h (P < 0.01) later. B_15–42 peptide increased by 0.63 pmol · ml^–1 (P<0.001),d-dimer by 68.3 ng · ml^–1 (P< 0.05). Euglobulin lysis time (ELT) was reduced from 109 to 18 min (P<0.001). The increased t-PA activity and t-PA antigen concentration disappeared in the course of the first 3 h after exertion. ELT also reached its pre-exercise levels at this time. Thirty-one hours after the race ELT and t-PA antigen levels were slightly but significantly reduced (P<0.05), whereas B_15–42 peptide remained increased (P<0.05). t-PA activity was unchanged compared with pre-exercise values. It seems that the exercise-induced FA is mainly caused by the marked increase of t-PA antigen and t-PA activity.     

静息时或运动后Q—Tc延长诊断冠心病价值的探讨

用自行设计的踏车多指标心血管功能评价系统(E系统),对正常人,冠心病患者、心肌梗塞患者三组进行踏车运动前后Q—Tc变化及运动前后心血管功能评定。对静息时或运动后Q—Tc延长诊断冠心病价值及运动前后心血管功能变化规律的敏感性、特殊性分别进行对照和探讨。     

Nocturnal hormonal responses to resistance exercise

The effects of resistance exercise on the nocturnal responses of cortisol (CO), testosterone (TEST), human growth hormone (hGH), and thyroid hormones (T₃, T₄) were examined in eight trained weight lifters. Each subject completed two trials using a counterbalanced design: a control, no exercise trial (CON) and a heavy resistance exercise session of three sets of six exercises to exhaustion (RE). The exercise session took place between 1900 and 2000 hours. Blood was sampled prior to and at 20-min intervals after RE. For both trials blood was sampled at hourly intervals from 2100 hours until 0700 hours. The hGH and CO concentrations were increased up to 40-min post-exercise (P < 0.05), but returned to resting levels 1 h post-exercise. Nocturnal hGH concentration was not affected by RE (P > 0.26) and peaked at 0200 hours and declined until 0700 hours. Similarly, the CO responses were similar between the trails (P > 0.14). This CO concentrations declined from 2200 hours until 0100 hours, then increased steadily until 0700 hours. The TEST concentrations during both trials rose steadily from 2200 hours until 0700 hours; however, the rise in TEST from 0500–0700 hours during RE was greater than during the CON trails (P = 0.059). The T₃ concentrations were unchanged by exercise and were similar at all times between trails. The T₄ concentrations were elevated for 20 min after RE; however nocturnal T₄ concentrations were lower after RE than during CON. These results would suggest that bGH and CO may have limited nocturnal reactivity to resistance exercise. However, the nocturnal alterations of TEST and T4 after resistance exercise, although small, may have implications for muscle anabolism.     

Power and peak blood lactate at 5050 m with 10 and 30 s ‘all out’ cycling

Anecdotal observations suggest that the reduction in peak lactate accumulation in blood ([La]_{b peak}) after exhausting exercise, in chronic hypoxia vs. normoxia, may be related to the duration of the exercise protocol, being less pronounced after short supramaximal exercise than after incremental exercise (IE) lasting several minutes. To test this hypothesis, six healthy male Caucasians (age 36.8 ± 7.3, x¯ ± SD) underwent three exercise protocols on a cycle ergometer, at sea level (SL) and after 21 ± 10 days at 5050 m altitude (ALT): (1) 10 s, (2) 30 s ‘all out’ exercise and (3) IE leading to exhaustion in ～20–25 min. ‘Average’ power output (p¯) was calculated for 10 or 30 s ‘all out’; maximal power output (P_max) was determined for IE. Lactate concentration in arterialized capillary blood ([La]_b) was measured at rest and at different times during recovery; the highest [La]_b during recovery was taken as [La]_{b peak}. No significant differences in p¯ were observed between SL and ALT, for either 10 or 30 s ‘all out’ exercise; P_max during IE was significantly lower at ALT than at SL. [La]_{b peak} after 10 s ‘all out’ was unaffected by chronic hypoxia (7.0 ± 0.9 at ALT vs. 6.3 ± 1.8 mmol L^–1 at SL). After 30 s ‘all out’ the [La]_{b peak} decrease, at ALT (10.6 ± 0.6 mmol L^–1) vs. SL (12.9 ± 1.4 mmol L^–1), was only ～50% of that observed for IE (6.7 ± 1.6 mmol L^–1 vs. 11.3 ± 2.8 mmol L^–1). Muscle power output and blood lactate accumulation during short supramaximal exercise are substantially unaffected by chronic hypoxia.