Aivaras Ratkevicius

Effect of training on contractile and metabolic properties of wrist extensors in spinal cord-injured individuals.

Paretic human muscle rapidly loses strength and oxidative endurance, and electrical stimulation training may partly reverse this. We evaluated the effects of two training protocols on the contractile and metabolic properties of the wrist extensor in 12 C‐5/6 tetraplegic individuals. The wrist extensor muscles were stimulated for 30 min/day, 5 days/week, for 12 weeks, using either a high‐resistance (Hr) or a low‐resistance (Lr) protocol. Total work output was similar in both protocols. The nontrained arm was used as a control. Maximum voluntary torque increased in the Hr (P < 0.05) but not the Lr group. Electrically stimulated peak tetanic torque at 15 HZ, 30 HZ, and 50 HZ were unchanged in the Lr group and tended to increase only at 15 HZ (P < 0.1) in the Hr group. Resistance to fatigue, however, increased (P < 0.05) in both Hr (42%) and Lr (41%) groups. Muscle metabolism was evaluated by 31P nuclear magnetic resonance spectroscopy (31P‐NMRS) during and following a continuous 40‐s 10‐HZ contraction. In the Hr group the cost of contraction decreased by 38% (P < 0.05) and the half‐time of phosphocreatine (PCr) recovery was shortened by 52% (P < 0.05). Thus, long‐term electrically induced stimulation of the wrist extensor muscles in spinal cord injury (SCI) increases fatigue resistance independent of training pattern. However, only the Hr protocol increased muscle strength and was shown to improve muscle aerobic metabolism after training. Muscle Nerve 27: 72–80, 2003

Energy metabolism of the gastrocnemius and soleus muscles during isometric voluntary and electrically induced contractions in man

1 Phosphocreatine (PCr) and intracellular pH detected by 31P NMR in the gastrocnemius and soleus muscles were evaluated in order to compare the anaerobic ATP costs of voluntary and electrically induced exercise. Continuous isometric contraction at 40 % of maximum force and repeated isometric contractions at approximately 75 % of maximum force (contraction plus relaxation period of 0.5 s plus 2 s) were studied. 2 Anaerobic ATP turnover in soleus and gastrocnemius muscles was slower during continuous voluntary contraction than during continuous electrically induced contraction (0.36 ± 0.04 versus 0.63 ± 0.05 mmol (kg wet wt)−1 s−1, P < 0.05, in soleus; 0.19 ± 0.03 versus 1.04 ± 0.04 mmol (kg wet wt)−1 s−1, P < 0.001, in gastrocnemius). 3 There was no significant difference in anaerobic ATP turnover between voluntary and electrically induced exercise when repeated brief contractions were performed (0.22 ± 0.05 and 0.30 ± 0.04 mmol (kg wet wt)−1 s−1, respectively, for the soleus muscle and 0.57 ± 0.03 and 0.66 ± 0.07 mmol (kg wet wt)−1 s−1, respectively, for the gastrocnemius muscle). 4 During continuous voluntary contraction, in contrast to continuous stimulated contraction, anaerobic ATP turnover was slower (P < 0.05) in the gastrocnemius than in the soleus muscle, which also showed a higher electromyogram amplitude (41.1 ± 1.1 % of maximum) than the medial gastrocnemius muscle (21.4 ± 3.6 % of maximum, P < 0.001). 5 Anaerobic ATP turnover was faster (P < 0.05) in the gastrocnemius than in the soleus muscle during brief voluntary and brief electrically induced contractions. 6 The results show that the anaerobic ATP costs were higher for electrically induced exercise than for voluntary exercise when continuous submaximal contraction was performed but not when brief high‐intensity contractions were performed. The gastrocnemius muscle contributes to total force production relatively less than the soleus muscle during continuous voluntary plantar flexion at 40 % of the maximum voluntary contraction.

Blockades of mitogen-activated protein kinase and calcineurin both change fibre-type markers in skeletal muscle culture

Abstract. Activation of either the calcineurin or the extracellular signal-regulated kinase (ERK1/2) pathway increases the percentage of slow fibres in vivo suggesting that both pathways can regulate fibre phenotypes in skeletal muscle. We investigated the effect of calcineurin blockade with cyclosporin A and mitogen-activated protein kinase kinase (MEK1/2) blockade with U0126 upon myosin heavy chain (MHC) isoform mRNA levels and activities of metabolic enzymes after 1xa0day, 3xa0days and 7xa0days of treatment in primary cultures of spontaneously twitching rat skeletal muscle. U0126 treatment significantly decreased MHC Iβ mRNA levels and significantly increased MHC IIX, MHC IIB, embryonal MHC and perinatal MHC mRNA levels when compared to control. In addition, U0126 treatment significantly increased lactate dehydrogenase, creatine kinase, hexokinase, malate dehydrogenase and β-hydroxyacyl-CoA dehydrogenase activities above control values while a significant reduction in the percentage of pyruvate dehydrogenase in the active form was also observed. Calcineurin blockade significantly decreased both MHC Iβ and embryonal mRNA levels below control and significantly increased MHC IIX mRNA levels. Significant increases in the activities of both lactate dehydrogenase and creatine kinase above control values were also seen following cyclosporin A treatment. In conclusion, the results suggest that calcineurin upregulates slow-fibre genes and suppresses fast-fibre genes. Similarly, the ERK1/2 pathway upregulates slow-fibre MHC and suppresses fast-fibre MHC isoforms. However, the effect on enzyme activities is not fibre-type specific. The effect of U0126 on the percentage of pyruvate dehydrogenase in the active form suggests that the ERK1/2 pathway may also be involved in regulation of the phosphorylation state of this enzyme.

Metabolic costs of force generation for constant-frequency and catchlike-inducing electrical stimulation in human tibialis anterior muscle.

Metabolic costs of force generation were compared for constant‐frequency and catchlike‐inducing electrical stimulation. Repetitive catchlike‐inducing trains consisted of 2 interpulse intervals (IPIs) at 12.5 ms, 1 IPI at 25 ms, and 5 IPIs at 50 ms. Constant‐frequency trains consisted of 8 IPIs at 37.5 ms. One train was delivered to the peroneal nerve every 2.5 s for 36 times under ischemic conditions. Anaerobic adenosine triphosphate (ATP) turnover was determined using 31‐phosphorus magnetic resonance spectroscopy (P‐MRS) of the human tibialis anterior muscle. Compared with constant‐frequency trains, catchlike‐inducing trains produced a faster force generation and were more effective in maintaining the force–time integral as well as peak force. However, ATP costs of force generation were similar for the catchlike‐inducing and constant‐frequency stimulation (6.7 ± 1.1 and 6.6 ± 1.0 μmol ATP/kg wet weight/N·s, respectively, P = 0.601). This suggests that the positive effects of catchlike‐inducing stimulation on force maintenance are mediated by potentiated Ca2+ release from the sarcoplasmic reticulum rather than by lower metabolic costs of muscle force generation. Our findings also suggest that catchlike‐inducing stimulation produces larger forces in fatigued muscle than constant‐frequency trains and thus may be beneficial for muscle training or rehabilitation when muscle loading needs to be maintained in repetitive contractions.

No Effect of Antioxidant Supplementation in Triathletes on Maximal Oxygen Uptake, 31P-NMRS Detected Muscle Energy Metabolism and Muscle Fatigue

A double-blind placebo-controlled cross-over trial was undertaken to evaluate the effect of antioxidant supplementation on maximal oxygen uptake during bicycling, 31-phosphorus nuclear magnetic response spectroscopy (31P-NMRS) detected muscle energy metabolism during plantar flexion and muscle fatigue evaluated by 1-s electrical stimulation at low (10 Hz) and high (50 Hz) frequency. Seven male triathletes received daily oral antioxidant supplementation in capsule form including 100 mg coenzyme Q10 (CoQ10), 600 mg ascorbic acid and 270 mg alpha-tocopherol or placebo over a 6-week interval. Serum concentration of CoQ10 was significantly higher in the antioxidant phase (1.80+/-1 microg x ml(-1), mean +/- SD) than control (0.9+/-0.21 microg ml(-1)) or placebo phase (0.9+/-0.3 microg x ml(-1)) (P<0.01). Maximal oxygen uptake was 63.8+/-3.0 ml x min(-1) x kg(-1) in the control phase, and did not change significantly in the antioxidant (67.6+/-10.8 ml x min(-1) x kg(-1)) or the placebo phase (61.9+/-4.5 ml x min(-1) x kg(-1)). The combined 31P-NMRS/low frequency fatigue test (plantar flexion of the foot) did not show differences in the gastrocnemius muscle pH (6.77+/-0.14), phosphocreatine reduction at the end of exercise (23+/-14% of rest) and half-time for recovery of phosphocreatine (33+/-12 sec) between the placebo and the antioxidant trial. No difference in muscle fatigue at 10 Hz electrical stimulation was found between the three phases. In conclusion, the results demonstrate no effect of antioxidative vitamin supplementation on maximal oxygen uptake, muscle energy metabolism or muscle fatigue in triathletes.

High expression of MHC I in the tibialis anterior muscle of a paraplegic patient.

A long‐term paraplegic man presented exclusively (>99%) myosin heavy chain I (MHC I) in the tibialis anterior muscle (TA). This was coupled to a slow speed of contraction, a high resistance to fatigue, and a rapid resynthesis of phosphocreatine after an electrically evoked fatiguing contraction when compared with the TA muscles of 9 other paraplegic individuals. In contrast, the MHC composition of his vastus lateralis, gastrocnemius, and soleus muscles was that expected of a muscle from a spinal cord injured individual. This information may be of clinical importance in terms of the expected morphological and functional adaptations of skeletal muscle to different types of electrical stimulation therapy.

Changes in oxygenation and phosphocreatine during exercise and recovery in relation to fiber types and capillary supply in human skeletal muscle

The purpose of this study was to examine the relationship between histochemical characteristics obtained from the gastrocnemius and changes in muscle energetics. Muscle oxygenation was determined by near infrared spectroscopy, and phosphocreatine (PCr) by 31-phosphorus magnetic resonance spectroscopy (31P-MRS) during a submaximal plantar flexion exercise and recovery. The relative occurrence (%) of slow-twitch fibers (ST), fast-twitch oxidative fibers (FTa), fast-twitch glycolytic fibers (FTb), and the number of capillaries per fiber (Cap/Fiber) were also determined. The sum of %ST and %FTa (%ST + %FTa) was 85.8 +/- 8.74% (mean +/- SD), while the number of Cap/Fiber was 2.52 +/- 0.63. The initial rate of deoxygenation (Ratedeoxy) at the beginning of the exercise was 2.43 +/- 0.95 %(DOT)sec-1. The time constants (Tc) for the recovery of PCr and muscle oxygenation after exercise were 22.1 +/- 6.3 sec. and 20.3 +/- 13.6 sec., respectively. The %ST + FTa, and the number of Cap/Fiber were each positively correlated to the Ratedeoxy (P < 0.05). The %ST + %FTa, and the number of Cap/Fiber were negatively correlated to the Tc for PCr recovery (P < 0.05), but not correlated to that for muscle oxygenation recovery. In conclusion, the Ratedeoxy during localized submaximal exercise, and the Tc for PCr recovery are indicators of the muscles oxidative capacity.