Strength training improves double-poling performance after prolonged submaximal exercise in cross-country skiers.

The purpose of this study was to investigate the effects of adding strength training with or without vibration to cross-country (XC) skiers' endurance training on double-poling (DP) performance, physiological, and kinematic adaptations. Twenty-one well-trained male XC-skiers combined endurance- and upper-body strength training three times per week, either with (n = 11) or without (n = 10) superimposed vibrations for 8 weeks, whereas eight skiers performed endurance training only (CON). Testing included 1RM in upper-body exercises, work economy, neural activation, oxygen saturation in muscle, and DP kinematics during a prolonged submaximal DP roller ski test which was directly followed by a time to exhaustion (TTE) test. TTE was also performed in rested state, and the difference between the two TTE tests (TTEdiff ) determined the ability to maintain DP performance after prolonged exercise. Vibration induced no additional effect on strength or endurance gains. Therefore, the two strength training groups were pooled (STR, n = 21). 1RM in STR increased more than in CON (P < .05), and there were no differences in changes between STR and CON in any measurements during prolonged submaximal DP. STR improved TTE following prolonged DP (20 ± 16%, P < .001) and revealed a moderate effect size compared to CON (ES = 0.80; P = .07). Furthermore, STR improved TTEdiff more than CON (P = .049). In conclusion, STR superiorly improved 1RM strength, DP performance following prolonged submaximal DP and TTEdiff , indicating a specific effect of improved strength on the ability to maintain performance after long-lasting exercise.

Measurement of regional forearm muscle haemodynamics via the near-infrared spectroscopy venous occlusion technique: the impact of hand circulatory occlusion.

The purpose of this study was to examine whether circulatory occlusion of the hand impacts on regional forearm muscle haemodynamics as determined by the near-infrared spectroscopy (NIRS) venous occlusion technique (NIRSVOT). Twenty-five young, healthy participants (18 males and 7 females; 28 ± 4 years; 71 ± 7 kg) completed two experimental protocols that were performed on the dominant arm: (1) a series of five venous occlusion trials with a suprasystolic cuff (>260 mmHg) applied to the wrist and (2) five venous occlusion trials without hand-occlusion. Both protocols were performed twice in a counterbalanced manner. NIRS data were obtained from the flexor digitorum superficialis (FDS) muscle using a dual wavelength, continuous-wave spectrophotometer. FDS muscle blood flow (Q(FDS)), vascular conductance (C(FDS)), O2 consumption (Vo(2FDS)), and venous O2 saturation (SvO2) were calculated from NIRS data during the initial 5 s of venous occlusion. Circulatory occlusion of the hand via wrist cuffing significantly (P < 0.05) reduced Q(FDS) (-36 ± 23%), CFDS (-37 ± 23%), Vo2(FDS) (-14 ± 31%) and SvO2 (-14 ± 12%). These findings indicate that hand-occlusion, via wrist cuffing, adversely impacts on regional forearm haemodynamics as determined by the NIRS-VOT. Consequently, it is recommended that future investigators avoid hand-occlusion when using the NIRS-VOT to quantify spontaneous haemodynamics of regional forearm muscle.

Effects of two weeks of daily apnea training on diving response, spleen contraction, and erythropoiesis in novel subjects.

Three potentially protective responses to hypoxia have been reported to be enhanced in divers: (1) the diving response, (2) the blood-boosting spleen contraction, and (3) a long-term enhancement of hemoglobin concentration (Hb). Longitudinal studies, however, have been lacking except concerning the diving response. Ten untrained subjects followed a 2-week training program with 10 maximal effort apneas per day, with pre- and posttraining measurements during three maximal duration apneas, and an additional post-training series when the apneic duration was kept identical to that before training. Cardiorespiratory parameters and venous blood samples were collected across tests, and spleen diameters were measured via ultrasound imaging. Maximal apneic duration increased by 44 s (P < 0.05). Diving bradycardia developed 3 s earlier and was more pronounced after training (P < 0.05). Spleen contraction during apneas was similar during all tests. The arterial hemoglobin desaturation (SaO2) nadir after apnea was 84% pretraining and 89% after the duration-mimicked apneas post-training (P < 0.05), while it was 72% (P < 0.05) after maximal apneas post-training. Baseline Hb remained unchanged after training, but reticulocyte count increased by 15% (P < 0.05). We concluded that the attenuated SaO2 decrease during mimic apneas was due mainly to the earlier and more pronounced diving bradycardia, as no enhancement of spleen contraction or Hb had occurred. Increased reticulocyte count suggests augmented erythropoiesis.

L-carnitine and creatine in Friedreich's ataxia. A randomized, placebo-controlled crossover trial.

Impaired oxidative phosphorylation is a crucial factor in the pathogenesis of Friedreich's ataxia (FA). L-carnitine and creatine are natural compounds that can enhance cellular energy transduction. We performed a placebo-controlled triple-phase crossover trial of L-carnitine (3 g/d) and creatine (6.75 g/d) in 16 patients with genetically confirmed FA. Primary outcome measures were mitochondrial ATP production measured as phosphocreatine recovery by 31Phosphorus magnetic resonance spectroscopy, neurological deficits assessed by the international co-operative ataxia rating scale and cardiac hypertrophy in echocardiography. After 4 months on L-carnitine phosphocreatine recovery was improved compared to baseline (p<0.03, t-test) but comparison to placebo and creatine effects did not reach significance (p=0.06, F-test). Ataxia rating scale and echocardiographic parameters remained unchanged. Creatine had no effect in FA patients. L-carnitine is a promising substance for the treatment of FA patients, and larger trials are warranted.

Adipose tissue thickness affects in vivo quantitative near-IR spectroscopy in human skeletal muscle.

The influence of adipose tissue thickness (ATT) on near-IR spectroscopy (NIRS) measurements in vivo was studied in the human flexor digitorum superficialis muscle at rest and during sustained isometric handgrip exercise. NIRS was used for the quantitative measurement of muscle O(2) consumption (mV.O(2)) and forearm blood flow (FBF) in 78 healthy subjects. Skinfold thickness ranged from 1.4 to 8.9 mm within the group. Resting mV.O(2) was 0.11+/-0.04 ml of O(2).min(-1).100 g(-1), and FBF was 1.28+/-0.82 ml.min(-1).100 ml(-1). There was a negative correlation (r=-0.70, P< or =0.01), indicating a decrease in mV.O(2) with increasing ATT. mV.O(2) in the 10 leanest subjects appeared to be twice as high as that in the 10 subjects with the highest ATT. A poor correlation (r=0.29, P< or =0.01) was found between ATT and FBF. The gender difference that we found for mV.O(2) was due to the difference in ATT between female and male subjects. No correlation was found between maximum voluntary contraction and mV.O(2), nor between maximum voluntary contraction and ATT, indicating that the contraction force did not confound our results. These results show that ATT has a substantial confounding influence on in vivo NIRS measurements, and that it is essential to incorporate this factor into future NIRS muscle studies in order to justify comparisons between different groups. To facilitate such comparisons, upper and lower boundaries for normal values of mV.O(2) and FBF in relation to ATT are presented.

Blood flow and muscle oxygen uptake at the onset and end of moderate and heavy dynamic forearm exercise.

We hypothesized that forearm blood flow (FBF) during moderate intensity dynamic exercise would meet the demands of the exercise and that postexercise FBF would quickly recover. In contrast, during heavy exercise, FBF would be inadequate causing a marked postexercise hyperemia and sustained increase in muscle oxygen uptake (VO(2musc)). Six subjects did forearm exercise (1-s contraction/relaxation, 1-s pause) for 5 min at 25 and 75% of peak workload. FBF was determined by Doppler ultrasound, and O(2) extraction was estimated from venous blood samples. In moderate exercise, FBF and VO(2musc) increased within 2 min to steady state. Rapid recovery to baseline suggested adequate O(2) supply during moderate exercise. In contrast, FBF was not adequate during heavy dynamic exercise. Immediately postexercise, there was an approximately 50% increase in FBF. Furthermore, we observed for the first time in the recovery period an increase in VO(2musc) above end-exercise values. During moderate exercise, O(2) supply met requirements, but with heavy forearm exercise, inadequate O(2) supply during exercise caused accumulation of a large O(2) deficit that was repaid during recovery.

Performance of near-infrared spectroscopy in measuring local O(2) consumption and blood flow in skeletal muscle.

The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV(O(2(Fick)))]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV(O(2)) increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV(O(2(Fick))) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV(O(2)) and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.

The effect of electrical stimulation on leg muscle pump activity in spinal cord-injured and able-bodied individuals.

The purpose of this study was to examine the difference in: (1) effective muscle pump activity (MPA) between voluntary and electrically (ES) induced contractions in able-bodied subjects (ABS); and (2) ES-induced MPA between spinal cord-injured (SCI) individuals and ABS. MPA was measured as relative volume changes in the calf using strain-gauge plethysmography during repeated muscle contractions in the supine position while venous outflow was impeded by a thigh cuff inflated to a range of pressures. Ten SCI individuals and ten ABS participated in this study. ABS showed no significant difference between voluntary and electrically induced MPA [58.1 (18.4)% versus 67.7 (8.7)%, respectively]. SCI individuals showed a significantly lower ES-induced MPA than ABS [21.5 (15.9)% versus 67.7 (8.7)%, respectively]. The low MPA in SCI individuals may be explained by: (1) extensive leg muscle atrophy and/or (2) an "atrophic" vascular system in the legs. The electrical current level seemed to influence MPA (43 mA, 21.5% versus 60 mA, 30.8%) for SCI individuals, whereas no influence of muscle contraction rate on MPA was observed in ABS. The results of this study demonstrate that although ES-induced leg muscle contractions result in adequate MPA in ABS, it leads to significantly less effective MPA in SCI individuals.

Quantitative near-infrared spectroscopy discriminates between mitochondrial myopathies and normal muscle.

Five patients with chronic progressive external ophthalmoplegia (CPEO) and 27 healthy controls were examined by near-infrared spectroscopy (NIRS) for the noninvasive and direct quantitative measurement of muscle oxygen consumption and forearm blood flow. NIRS measurements were obtained in rest and during static isometric handgrip exercise at 10% of the maximum voluntary contraction (MVC) force. A significantly decreased oxygen consumption at rest as well as during exercise was found in patients with CPEO. Our results suggest that NIRS is able to discriminate between CPEO patients and healthy controls, which makes NIRS a valuable tool in the diagnostic workup of patients suspected to have a mitochondrial myopathy.

Quantitative measurement of oxygen consumption and forearm blood flow in patients with mitochondrial myopathies.

Five patients with chronic progressive external ophthalmoplegia (CPEO) and 27 healthy controls were examined by near-infrared spectroscopy (NIRS) for the non-invasive and direct quantitative measurement of muscle oxygen consumption during rest as well as during static isometric handgrip exercise at 10% of their maximum voluntary contraction. In patients with CPEO, we found a significantly decreased oxygen consumption during exercise, but more remarkably already during rest. Our results suggest that NIRS is able to discriminate between CPEO patients and healthy controls, which makes NIRS a promising tool in the diagnostic work-up of patients suspected of a mitochondrial myopathy.