Neuromuscular manifestations of work-related myalgia in women specific to extensor carpi radialis brevis.

This study assessed neuromuscular function in the extensor carpi radialis brevis (ECRB) of female workers diagnosed with work-related myalgia (WRM, n = 14, age 45.2 ± 1.9 years) and the ECRB of healthy controls (CON, n = 10, age 34.6 ± 2.5 years). Groups were compared on voluntary and electrically evoked functional responses at rest (Pre), immediately following a 5 min repetitive task (Post-0) performed at 60% maximal voluntary contraction (MVC), and after 5 min of recovery (Post-5). Despite near complete motor unit activation (MUA) (CON 98% ± 1% vs. WRM 99% ± 1%), at Pre, WRM produced 26% less (P < 0.05) MVC force than CON. Following an MVC, twitch force was increased (P < 0.05) by 94% ± 13% and 54% ± 11% in CON and WRM, respectively (CON vs. WRM; P < 0.05). The peak force and the maximal rates of force development and decline of electrically evoked contractions (10-100 Hz) were generally depressed (P < 0.05) at Post-0 and Post-5 relative to Pre. The response pattern to increasing frequencies of stimulation was not different (P > 0.05) between groups and MUA was not impaired (CON 97% ± 1% vs. WRM 97% ± 1%; P > 0.05). In conclusion, the peripheral weakness observed in the ECRB in WRM at rest does not result in abnormal fatigue or recovery responses after performing a task controlled for relative demand (60% MVC).

Sarcoplasmic Reticulum Phospholipid Fatty Acid Composition and Sarcolipin Content in Rat Skeletal Muscle.

In a previous study, we reported lower sarcoplasmic reticulum (SR) Ca(2+) pump ionophore ratios in rat soleus compared to red and white gastrocnemius (RG, WG) muscles which may be indicative of greater SR Ca(2+) permeability in soleus. Here we assessed the lipid composition of the SR membranes obtained from these muscles to determine if SR docosahexaenoic acid (DHA) content and fatty acid unsaturation could help to explain the previously observed differences in SR Ca(2+) permeability. Since we have shown previously that sarcolipin may also influence SR Ca(2+) permeability, we also examined the levels of sarcolipin in rat muscle. We found that SR membrane DHA content was significantly higher in soleus (5.3 ± 0.2 %) compared to RG (4.2 ± 0.2 %) and WG (3.3 ± 0.2 %). Likewise, total SR membrane unsaturation and unsaturation index (UI) were significantly higher in soleus (% unsaturation: 59.1 ± 2.4; UI: 362.9 ± 0.8) compared to RG (% unsaturation: 55.3 ± 1.0; UI: 320.9 ± 2.5) and WG (% unsaturation: 52.6 ± 1.1; UI: 310. ± 2.2). Sarcolipin protein was 17-fold more abundant in rat soleus compared to RG and was not detected in WG; however, comparisons between soleus, RG, and WG in sarcolipin-null mice revealed that, in the absence of sarcolipin, ionophore ratios are still lowest in soleus and highest in WG. Overall, our results suggest that SR membrane DHA content and unsaturation, and, in part, sarcolipin expression may contribute to SR Ca(2+) permeability and, in turn, may have implications in muscle-based metabolism and diet-induced obesity.

Cellular properties of extensor carpi radialis brevis and trapezius muscles in healthy males and females.

In this study, we sought to determine whether differences in cellular properties associated with energy homeostasis could explain the higher incidence of work-related myalgia in trapezius (TRAP) compared with extensor carpi radialis brevis (ECRB). Tissue samples were obtained from the ECRB (n = 19) and TRAP (n = 17) of healthy males and females (age 27.9 ± 2.2 and 28.1 ± 1.5 years, respectively; mean ± SE) and analyzed for properties involved in both ATP supply and utilization. The concentration of ATP and the maximal activities of creatine phosphokinase, phosphorylase, and phosphofructokinase were higher (P < 0.05) in ECRB than TRAP. Succinic dehydrogenase, citrate synthase, and cytochrome c oxidase were not different between muscles. The ECRB also displayed a higher concentration of Na(+)-K(+)-ATPase and greater sarcoplasmic reticulum Ca(2+) release and uptake. No differences existed between muscles for either monocarboxylate transporters or glucose transporters. It is concluded that the potentials for high-energy phosphate transfer, glycogenolysis, glycolysis, and excitation-contraction coupling are higher in ECRB than TRAP. Histochemical measurements indicated that the muscle differences are, in part, related to differing amounts of type II tissue. Depending on the task demands, the TRAP may experience a greater metabolic and excitation-contraction coupling strain than the ECRB given the differences observed.

Preliminary observations on high energy phosphates and metabolic pathway and transporter potentials in extensor carpi radialis brevis and trapezius muscles of women with work-related myalgia.

This study compared both the extensor carpi radialis brevis (ECRB) and the trapezius (TRAP) muscles of women with work-related myalgia (WRM) with healthy controls (CON) to determine whether abnormalities existed in cellular energy status and the potentials of the various metabolic pathways and segments involved in energy production and substrate transport. For both the ECRB (CON, n = 6-9; WRM, n = 13) and the TRAP (CON, n = 6-7; WRM, n = 10), no differences (P > 0.05) were found for the concentrations (in millimoles per kilogram of dry mass) of ATP, PCr, lactate, and glycogen. Similarly, with one exception, the maximal activities (in moles per milligram of protein per hour) of mitochondrial enzymes representative of the citric acid cycle (CAC), the electron transport chain (ETC), and ß-oxidation, as well as the cytosolic enzymes involved in high energy phosphate transfer, glycogenolysis, glycolysis, lactate oxidation, and glucose phosphorylation were not different (P > 0.05). The glucose transporters GLUT1 and GLUT4, and the monocarboxylate transporters MCT1 and MCT4, were also normal in WRM. It is concluded that, in general, abnormalities in the resting energy and substrate state, the potential of the different metabolic pathways and segments, as well as the glucose and monocarboxylate transporters do not appear to be involved in the cellular pathophysiology of WRM.

Excitation-contraction coupling properties in women with work-related myalgia: a preliminary study.

We investigated the potential role of selected excitation-contraction coupling processes in females with work-related myalgia (WRM) by comparing WRM with healthy controls (CON) using tissue from extensor carpi radialis brevis (ECRB) and trapezius (TRAP) muscles. For the ECRB, age (mean ± SE) was 29.6 ± 3.5 years for CON (n = 9) and 39.2 ± 2.8 years for WRM (n = 13), while for the TRAP, the values were 26.0 ± 2.1 years for CON (n = 7) and 44.6 ± 2.9 years for WRM (n = 11). For the sarcoplasmic reticulum (SR) of the ECRB, WRM displayed concentrations (nmol·(mg protein)(-1)·min(-1)) that were lower (P < 0.05) for Total (202 ± 4.4 vs 178 ± 7.1), Basal (34 ± 1.6 vs 30.1 ± 1.3), and maximal Ca(2+)-ATPase activity (Vmax, 168 ± 4.9 vs 149 ± 6.3), and Ca(2+)-uptake (5.06 ± 0.31 vs 4.13 ± 0.29), but not SERCA1a and SERCA2a isoforms, by comparison with CON. When age was incorporated as a co-variant, Total, Basal, and Ca(2+)-uptake remained different from CON (P < 0.05), but not Vmax (P = 0.13). For TRAP, none of the ATPase properties differed between groups (P > 0.05) either before or following adjustment for age. No differences (P > 0.05) were observed between the groups for Ca(2+)-release in the SR for either TRAP or ECRB. Similarly, no deficiencies, regardless of muscle, were noted for either the Na(+)-K(+)-ATPase content or the α and ß subunit isoform distribution in WRM. This preliminary study provides a basis for further research, with expanded numbers, investigating the hypothesis that abnormalities in SR Ca(2+)-regulation are involved in the cellular etiology of WRM.

A pilot study to determine whether differences exist in histochemical properties between the trapezius and extensor carpi radialis brevis muscles in women with work-related myalgia.

To investigate fibre-type abnormalities in women with work-related myalgia (WRM), tissue samples were extracted from their trapezius (TRAP) and the extensor carpi radialis brevis (ECRB) muscles and compared with healthy controls (CON). For the ECRB samples (CON, n = 6; WRM, n = 11), no differences (P > 0.05) were found between groups for any of the properties examined, namely fibre-type (I, IIA, IIX, IIAX) distribution, cross-sectional fibre area, capillary counts (CC), capillary to fibre area ratio, and succinic dehydrogenase activity. For the TRAP samples (CON, n = 6; WRM, n = 8), the only difference (P < 0.05) observed between groups was for CC (CON > WRM), which was not statistically significant (P > 0.05) when age was used a covariant. A comparison of the properties of these 2 muscles in the CON group indicated a higher (P < 0.05) and lower (P < 0.05) percentage of type I and type IIA fibres, respectively, in the TRAP as well as higher (P < 0.05) CC, which was not specific to fibre type. These preliminary results suggest that the properties employed to characterize fibre types do not differentiate CON from WRM for either the TRAP or ECRB. As a consequence, the role of inherent fibre-type differences between these muscles in the pathogenesis of WRM remains uncertain.

Role of exercise duration on metabolic adaptations in working muscle to short-term moderate-to-heavy aerobic-based cycle training.

This study aimed at investigating the relative roles of the duration versus intensity of exercise on the metabolic adaptations in vastus lateralis to short-term (10 day) aerobic-based cycle training. Healthy males with a peak aerobic power (VO2 peak) of 46.0 ± 2.0 ml kg(-1) min(-1) were assigned to either a 30-min (n = 7) or a 60-min (n = 8) duration performed at two different intensities (with order randomly assigned), namely moderate (M) and heavy (H), corresponding to 70 and 86 % VO2 peak, respectively. No change (P > 0.05) in VO2 peak was observed regardless of the training program. Based on the metabolic responses to prolonged exercise (60 % VO2 peak), both M and H and 30 and 60 min protocols displayed less of a decrease (P < 0.05) in phosphocreatine (PCr) and glycogen (Glyc) and less of an increase (P < 0.05) in free adenosine diphosphate (ADPf), free adenosine monophosphate (AMPf), inosine monophosphate (IMP) and lactate (La). Training for 60 min compared with 30 min resulted in a greater protection (P < 0.05) of ADPf, AMPf, PCr and Glyc during exercise, effects that were not displayed between M and H. The reduction in both VO2 and RER (P < 0.05) observed during submaximal exercise did not depend on training program specifics. These findings indicate that in conjunction with our earlier study (Green et al., Eur J Appl Physiol, 2012b), a threshold exists for duration rather than intensity of aerobic exercise to induce a greater training impact in reducing metabolic strain.

Adaptations in muscle metabolic regulation require only a small dose of aerobic-based exercise.

This study investigated the hypothesis that the duration of aerobic-based cycle exercise would affect the adaptations in substrate and metabolic regulation that occur in vastus lateralis in response to a short-term (10 day) training program. Healthy active but untrained males (n = 7) with a peak aerobic power ([Formula: see text]) of 44.4 ± 1.4 ml kg(-1) min(-1) participated in two different training programs with order randomly assigned (separated by ≥2 weeks). The training programs included exercising at a single intensity designated as light (L) corresponding to 60 % [Formula: see text], for either 30 or 60 min. In response to a standardized task (60 % [Formula: see text]), administered prior to and following each training program, L attenuated the decrease (P < 0.05) in phosphocreatine and the increase (P < 0.05) in free adenosine diphosphate and free adenosine monophosphate but not lactate. These effects were not altered by daily training duration. In the case of muscle glycogen, training for 60 versus 30 min exaggerated the increase (P < 0.05) that occurred, an effect that extended to both rest and exercise concentrations. No changes were observed in [Formula: see text] measured during progressive exercise to fatigue or in [Formula: see text] and RER during submaximal exercise with either training duration. These findings indicate that reductions in metabolic strain, as indicated by a more protected phosphorylation potential, and higher glycogen reserves, can be induced with a training stimulus of light intensity applied for as little as 30 min over 10 days. Our results also indicate that doubling the duration of daily exercise at L although inducing increased muscle glycogen reserves did not result in a greater metabolic adaptation.

Can increases in capillarization explain the early adaptations in metabolic regulation in human muscle to short-term training?

To investigate the hypothesis that increases in fibre capillary density would precede increases in oxidative potential following training onset, tissue was extracted from the vastus lateralis prior to (0 days) and following 3 and 6 consecutive days of submaximal cycle exercise (2 h·day(-1)). Participants were untrained males (age = 21.4 ± 0.58 years; peak oxygen consumption = 46.2 ± 1.6 mL·kg(-1)·min(-1); mean ± standard error (SE)). Tissue was assessed for succinic dehydrogenase activity (SDH) by microphotometry and indices of capillarization based on histochemically assessed area and capillary counts (CC) in specific fibre types. Three days of training (n = 13) resulted in a generalized decrease (p < 0.05) in fibre area (-14.2% ± 3.0%; mean ± SE) and increase (p < 0.05) in CC/Area (20.4% ± 2.7%) and no change in either CC or SDH activity. Following 6 days of treatment (n = 6), increases (p < 0.05) in CC (18.2% ± 4.2%), CC/Area (28.9% ± 3.2%), and SDH activity (22.9% ± 6.0%) occurred that was not specific to major fibre type. No changes in either fibre area or fibre-type distribution were observed with additional training. We conclude that increases in angiogenic-based capillary density and oxidative potential occur coincidentally following training onset, while increases in capillary density, mediated by reductions in fibre area, represent an initial isolated response, the significance of which may be linked to the metabolic alterations that also result.

Muscle cellular properties in the ice hockey player: a model for investigating overtraining?

In this study, we hypothesized that athletes involved in 5-6 months of sprint-type training would display higher levels of proteins and processes involved in muscle energy supply and utilization. Tissue was sampled from the vastus lateralis of 13 elite ice hockey players (peak oxygen consumption = 51.8 ± 1.3 mL·kg(-1)·min(-1); mean ± standard error) at the end of a season (POST) and compared with samples from 8 controls (peak oxygen consumption = 45.5 ± 1.4 mL·kg(-1)·min(-1)) (CON). Compared with CON, higher activities were observed in POST (p < 0.05) only for succinic dehydrogenase (3.32 ± 0.16 mol·(mg protein)(-1)·min(-1) vs. 4.10 ± 0.11 mol·(mg protein)(-1)·min(-1)) and hexokinase (0.73 ± 0.05 mol·(mg protein)(-1)·min(-1) vs. 0.90 ± 0.05mol·(mg protein)(-1)·min(-1)) but not for phosphorylase, phosphofructokinase, and creatine phosphokinase. No differences were found in Na(+),K(+)-ATPase concentration (ß(max): 262 ± 36 pmol·(g wet weight)(-1) vs. 275 ± 27 pmol·(g wet weight)(-1)) and the maximal activity of the sarcoplasmic reticulum Ca(2+)-ATPase (98.1 ± 6.1 µmol·(g protein)(-1)·min(-1) vs. 102 ± 3.3 µmol·(g protein)(-1)·min(-1)). Cross-sectional area was lower (p < 0.05) in POST but only for the type IIA fibres (6312 ± 684 µm(2) vs. 5512 ± 335 µm(2)), while the number of capillary counts per fibre and the capillary to fibre area ratio were generally higher (p < 0.05). These findings suggest that elite trained ice hockey players display elevations only in support of glucose-based aerobic metabolism that occur in the absence of alterations in excitation-contraction processes.

Association of peak aerobic power with capillary density but not oxidative potential in human vastus lateralis muscle.

In this study, we have postulated that in healthy males, peak aerobic power ([Formula: see text]) would associate with muscle capillary density rather than oxidative potential, regardless of fibre type or subtype. To test this, active but untrained volunteers (n = 11) were separated into high (HI) and low (LO) groups based on [Formula: see text] obtained during a progressive cycle task to fatigue. The 26% higher (P < 0.05) [Formula: see text] observed in HI (40.8 ± 1.5 mL·kg(-1)·min(-1), mean ± SE) compared with LO ( 51.4 ± 0.90 mL·kg(-1)·min(-1), mean ± SE) was not accompanied by differences in age (21.3 ± 1.2 compared with 21.1 ± 0.63 years, respectively) or body mass (72.4 ± 4.6 compared with 71.6 ± 1.9 kg, respectively). Tissue samples obtained from the vastus lateralis indicated greater (P < 0.05) capillary counts per fibre (CC; +24%) in HI compared with LO, regardless of fibre type (I, IIA, IIX, IIAX). Capillary density (CD) as measured in a field of defined area was also elevated (+22%; P < 0.05), as was the number of capillaries per fibre (+22%; P < 0.05). No differences were observed between the 2 groups in the distribution, area, and the CC/fibre area ratio in the different fibre types and subtypes. Similarly, there was no difference between the HI and LO groups in oxidative potential, as measured by succinic dehydrogenase activity in the different fibre types. It is concluded that the higher capillary density may contribute to improved vascular conductance and the elevated [Formula: see text] observed in the untrained participants.

Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with 31P-MRS.

In this study, we examined muscle metabolic and acid-base status during incremental wrist extension exercise in the forearm of individuals with work-related myalgia (WRM). Eighteen women employed in full-time occupations involving repetitive forearm labor were recruited in this cross-sectional study. Nine of these women were diagnosed with WRM, while the other nine had no previous WRM history and were used as age-matched controls (Con). Phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([P(i)]) as well as intracellular pH (pH(i)) status during exercise in WRM and Con. We observed a 38% decreased work capacity in WRM compared with Con [0.18 W (SD 0.03) vs. 0.28 W (SD 0.10); P = 0.007]. Piecewise linear regression of the incremental exercise data revealed that the onset of a faster decrease in pH(i) (i.e., the pH threshold, pHT) and the onset of a faster increase in log([P(i)]/[PCr]) (i.e., the phosphorylation threshold, PT) occurred at a 14% relatively lower power output in WRM [pHT: 45.2% (SD 5.3) vs. 59.0% (SD 4.6), P < 0.001; PT: 44.8% (SD 4.3) vs. 57.8% (SD 3.1), P < 0.001; % of peak power output, Con vs. WRM, respectively]. Monoexponential modeling of the kinetics of [PCr] and pH(i) recovery following exercise demonstrated a slower (P = 0.005) time constant (tau) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower (P = 0.007) tau for pH(i) in WRM [370 s (SD 178)] vs. Con [179 s (SD 52)]. In conclusion, our results suggest that WRM is associated with an increased reliance on nonoxidative metabolism. Possible mechanisms include a reduction in local muscle blood flow and perfusion, an increased ATP cost of force production, or both.

Effects of consecutive days of exercise and recovery on muscle mechanical function.

PURPOSE: To investigate the effects of three consecutive days of prolonged exercise on muscle mechanical function, 12 volunteers (.VO(2peak) = 44.8 +/- 2.0 mL.kg(-1).min(-1), mean +/- SE) cycled at approximately 60% .VO(2peak) until fatigue. METHODS: Quadriceps muscle function was assessed before and after exercise on day 1 (E1) and day 3 (E3) and during three consecutive days of recovery (R1, R2, R3), using both voluntary and electrically induced contractions at various stimulation frequencies. RESULTS: Exercise on E1 and E3 resulted in a 40% (120 +/- 12 vs 72 +/- 10 N) and 35% (117 +/- 14 vs 78 +/- 8 N) deficit (P < 0.05) in force at 10 Hz, respectively, which remained depressed (P < 0.05) by 32-34% during R1-R3. At 100 Hz, force, although not altered by exercise at E1 or E3, was decreased (P < 0.05) by 12-16% during recovery. The maximal rate of relaxation (-dF/dtmax) at 10 Hz was reduced (P < 0.05) by 38% on E1, by 32% on E3, and remained depressed by 38% through R3. At 100 Hz, -dF/dtmax was only depressed (P < 0.05) during recovery. Maximal rate of force development (+dF/dtmax) at 10 Hz was reduced (P < 0.05) by exercise, but not in recovery. Maximal voluntary contraction force was depressed (P < 0.05) with exercise at both E1 and E3 and remained depressed (P < 0.05) throughout recovery. The reduction (P < 0.05) in motor unit activation assessed with the interpolated twitch technique, observed during recovery, suggests that part of the incomplete recovery (weakness) is central in origin. CONCLUSIONS: These results demonstrate that three consecutive days of prolonged exercise result in a weakness that persists for at least 3 d, compromising force during both voluntary and induced contractions.

Mechanical and metabolic responses with exercise and dietary carbohydrate manipulation.

PURPOSE: To investigate the effects of altered muscle glycogen content on the mechanical and metabolic responses to prolonged exercise of moderate intensity. METHODS: Eight volunteers (.VO2peak = 49.3 +/- 1.2 mL.kg(-1).min(-1)) cycled to fatigue on two occasions: after a 3-d low-carbohydrate diet (Lo CHO), which had been preceded by glycogen-depleting exercise, and then after a 3-d high-carbohydrate diet (Hi CHO). Metabolic and mechanical properties were assessed at both Lo CHO and Hi CHO before exercise (Pre), at 30 min of exercise (30 min), at fatigue in Lo CHO (Post 1), and again at fatigue after a brief rest (Post 2). RESULTS: For the Lo CHO cycle, time to fatigue averaged 66.7 +/- 4.5 and 9.5 +/- 1.7 min for Post 1 and Post 2, respectively. For Hi CHO, Post 2 time to fatigue was 64.9 +/- 6.3 min. Muscle glycogen was elevated (P < 0.05) by approximately 40% in Hi CHO compared with Lo CHO. Phosphocreatine, although higher (P < 0.05) by approximately 25% during exercise in Hi CHO, was not different at Pre. Similar but reciprocal effects (P < 0.05) were observed for inorganic phosphate and creatine. Force at low frequencies of stimulation was maximally reduced (P < 0.05) by approximately 26-38% by 30 min of exercise, regardless of condition. CONCLUSION: A 7-d exercise-dietary protocol leads to both an elevation in muscle glycogen and improved energy homeostasis during exercise. Although these adaptations may explain the improved cycle performance, they are not related to the progression of muscle fatigue as assessed statically at low frequencies of stimulation.

Deconditioning fails to explain peripheral skeletal muscle alterations in men with chronic heart failure.

It remains controversial whether the skeletal muscle alterations in chronic heart failure (CHF) are due to disease pathophysiology or result from chronic deconditioning. The purpose of this study was to compare the skeletal muscle of CHF patients to peak oxygen consumption (peak VO(2)) matched sedentary controls. It has been established that skeletal muscle abnormalities are related to the exercise intolerance observed in patients with CHF. We studied the skeletal muscle of sedentary controls and patients with CHF matched for age, gender and peak VO(2). Hypothesis testing for the effects of group (CHF vs. normal), gender, and the interaction group x gender were performed. For capillary density only gender (p = 0.002) and the interaction of group x gender (p = 0.007) were significantly different. For 3-hydroxyl coenzyme A (CoA) dehydrogenase only group effect (p = 0.004) was significantly different. Mean values for capillary density were 1.46 +/- 0.28 for CHF men versus 1.87 +/- 0.32 for sedentary control men, 1.40 +/- 0.32 for CHF women versus 1.15 +/- 0.35 for sedentary control women. The activities for 3-hydroxyl CoA dehydrogenase were 3.09 +/- 0.88 for CHF men versus 4.05 +/- 0.42 for sedentary control men, 2.93 +/- 0.72 for CHF women versus 3.51 +/- 0.78 for sedentary control women. This study suggests that women and men adapt to CHF differently: men develop peripheral skeletal muscle abnormalities that are not attributable to deconditioning; women do not develop the same pathologic responses in skeletal muscle when compared with normal women matched for aerobic capacity.

Left ventricular adaptations following short-term endurance training.

This study examined the effects of short-term endurance training (ET) on the left ventricular (LV) adaptation and functional response to a series of exercise challenges with increasing intensity. Eight untrained men, with a mean age of 19.4 +/- 0.5 (SE) yr, were studied before and after 6 days of ET consisting of cycling 2 h/day at 65% peak aerobic power (VO2max). LV ejection fraction and LV volumes were assessed by radionuclide angiography at rest and during exercise at three uninterrupted successive work rates corresponding to 53, 68, and 83% of VO2max, each lasting 20 min. ET produced a calculated plasma volume expansion of 11.4 +/- 2.2% (P < 0.05). The increase in plasma volume was accompanied by an increase in VO2max from 45.9 +/- 1.9 to 49.0 +/- 1.0 ml x kg(-1) x min(-1) (P < 0.01) and a decrease in maximal heart rate (197 +/- 2.3 to 188 +/- 1.0 beats/min; P < 0.01). Resting LV function was not changed, although there was a trend for higher stroke volumes (SVs) and improvement in the rapid filling phase of diastole (P = 0.08). Training induced an increase in exercise SV by 10.4, 10.2, and 7% at 53, 68, and 83% VO2max, respectively (P < 0.01). These changes were secondary to increases in end-diastolic volume, which increased significantly at each exercise work rate following training (139 +/- 6 to 154 +/- 6 ml at 53% VO2max, and from 136 +/- 5 to 156 +/- 5 ml at 83% VO2max; P < 0.01). End-systolic volumes were unchanged after ET. A significant bradycardia was observed both at rest (decreasing 7%) and exercise (decreasing 10.4%). LV ejection fraction during exercise was increased slightly by training, reaching significance at the highest work rate, after 60 min of exercise. (P < 0.05). Cardiac output was higher following training at the highest workload (20.8 +/- 2.2 vs. 22.9 +/- 3.1 l/min; P < 0.01). These data indicate that short-term training elicits rapid adaptation to the LV functional response exercise, with increases in SV being secondary to a Frank-Starling effect with minor changes in contractile performance. This produced a volume-induced bradycardia and increase in LV filling, which may be of benefit during prolonged exercise.

Dietary docosahexaenoic acid supplementation reduces SERCA Ca2+ transport efficiency in rat skeletal muscle.

Docosahexaenoic acid (DHA) can reduce the efficiency and increase the energy consumption of Na(+)/K(+)-ATPase pump and mitochondrial electron transport chain by promoting Na(+) and H(+) membrane permeability, respectively. In skeletal muscle, the sarco(endo) plasmic reticulum Ca(2+)-ATPase (SERCA) pumps are major contributors to resting metabolic rate. Whether DHA can affect SERCA efficiency remains unknown. Here, we examined the hypothesis that dietary supplementation with DHA would reduce Ca(2+) transport efficiency of the SERCA pumps in skeletal muscle. Total lipids were extracted from enriched sarcoplasmic reticulum (SR) membranes that were isolated from red vastus lateralis skeletal muscles of rats that were either fed a standard chow diet supplemented with soybean oil or supplemented with DHA for 8 weeks. The fatty acid composition of total SR membrane lipids and the major phospholipid species were determined using electrospray ionization mass spectrometry (ESI-MS). After 8 weeks of DHA supplementation, total SR DHA content was significantly elevated (control, 4.1 ± 1.0% vs. DHA, 9.9 ± 1.7%; weight percent of total fatty acids) while total arachidonic acid was reduced (control, 13.5 ± 0.4% vs. DHA-fed, 9.4 ± 0.2). Similar changes in these fatty acids were observed in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, altogether indicating successful incorporation of DHA into the SR membranes post-diet. As hypothesized, DHA supplementation reduced SERCA Ca(2+) transport efficiency (control, 0.018 ± 0.0002 vs. DHA-fed, 0.014 ± 0.0009) possibly through enhanced SR Ca(2+) permeability (ionophore ratio: control, 2.8 ± 0.2 vs. DHA-fed, 2.2 ± 0.3). Collectively, our results suggest that DHA may promote skeletal muscle-based metabolism and thermogenesis through its influence on SERCA.

Molecular cloning and characterization of two Na/K-ATPase isoforms in Fundulus heteroclitus.

Na/K-ATPase plays an important role in ion regulation in teleost fishes. In most taxa several isoforms exist to provide physiological versatility to specific cell types, but little is known about Na/K-ATPase isoforms in fish. A reverse transcriptase polymerase chain reaction approach was used to identify Na/K-ATPase a-subunit isoforms from the gill and muscle of an estuarine teleost, Fundulus heteroclitus. Full-length complementary DNA sequences were similar at both the nucleotide level (74.4%) and the amino acid level (82.5%). Phylogenetic analysis indicated that the gill isoform was similar to the mammalian a1 subunit and the muscle isoform was similar to the mammalian a2 subunit. Northern blotting and isoform-specific polymerase chain reaction were used to determine the tissue distribution of the isoforms. The gill (a1) isoform was expressed in all tissues, while the muscle (a2) isoform had a much more restricted expression pattern, being present at high levels only in muscle and brain, consistent with the distributions of these isoforms in mammals.

Metabolic characteristics of experimental free vascularized canine gracilis muscle transfers.

A canine gracilis model was used to study muscle energy metabolism and enzyme activities after free vascularized muscle transfer. Fifteen male mongrel dogs underwent orthotopic, free transfer of the left gracilis with microneurovascular anastomosis. After a minimum of 10 months' recovery, muscle biopsy specimens were obtained from the transfers and the contralateral controls and analyzed for relative fiber type areas and maximum activities of phosphorylase, hexokinase, phosphofructokinase, glycerol-3-phosphate dehydrogenase (GPDH), pyruvate kinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, 3-hydroxyacyl coenzyme A dehydrogenase (HAD), and creatine phosphokinase. Biopsy specimens obtained before and after a 10 minute, 20-Hz contraction were analyzed for glucose, glycogen, glycolytic intermediates, phosphocreatine, total creatine, and adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, inosine monophosphate, and inosine). There was no significant transfer versus control difference in type I relative fiber area (45 +/- 4 percent versus 44 +/- 3 percent). Total creatine was significantly reduced in the transferred muscles relative to control (83.1 +/- 3.0 mmol/kg versus 100.6 +/- 5.1 mmol/kg dry weight). Maximal activities of phosphorylase, pyruvate kinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, HAD, and creatine phosphokinase were diminished in transfers relative to controls, although hexokinase activity was significantly higher in the freely transferred gracilis muscles. During the 20-Hz contraction, muscle transfers produced less force initially, although the force/time integral over the 10-minute stimulation was similar in transfers (277 +/- 25 N/g/second) and controls (272 +/- 24 N/g/second). The contraction was associated with significant glvcogen use and lactate accumulation in both transfers and controls, although this was less pronounced for the transfers. Glycolytic flux appeared muted in the transfers relative to controls. Significant, similar high-energy phosphagen reductions and inosine monophosphate accumulation were noted during the contraction in both groups. Contractile activity is associated with the expected pattern of muscle metabolite changes following free vascularized transfer, indicating the components of cellular energy metabolism are not qualitatively altered after microneurovascular muscle transfer. In contrast, quantitative differences suggest that free vascularized muscle transfer can be associated with a muscle enzyme profile consistent with deconditioning and the presence of denervated muscles fibers in the absence of fiber type profile changes.

Malleability of human skeletal muscle sarcoplasmic reticulum to short-term training.

This study investigated the hypothesis that adaptations would occur in the sarcoplasmic reticulum in vastus lateralis soon after the onset of aerobic-based training consistent with reduced Ca²âº-cycling potential. Tissue samples were extracted prior to (0 days) and following 3 and 6 days of cycling performed for 2 h at 60%-65% of peak aerobic power (VO2(peak)) in untrained males (VO2(peak) = 47 ± 2.3 mL·kg⁻¹·min⁻¹; mean ± SE, n = 6) and assessed for changes (nmol·mg protein⁻¹·min⁻¹) in maximal Ca²âº-ATPase activity (V(max)), Ca²âº-uptake, and Ca²âº-release (phase 1 and phase 2) as well as the sarcoplasmic (endoplasmic) reticulum Ca²âº-ATPase (SERCA) isoforms. Training resulted in reductions (p < 0.05) in SERCA1a at 6 days (-14%) but not at 3 days. For SERCA2a, reductions (p < 0.05) were also noted only at 6 days (-7%). For V(max), depressions (p < 0.05) were found at 6 days (172 ± 11) but not at 3 days (176 ± 13; p < 0.10) compared with 0 days (192 ± 11). These changes were accompanied by a lower (p < 0.05) Ca²âº-uptake at both 3 days (-39%) and 6 days (-48%). A similar pattern was found for phase 1 Ca²âº-release with reductions (p < 0.05) of 37% observed at 6 days and 23% (p = 0.21) at 3 days of training, respectively. In a related study using the same training protocol and participant characteristics, microphotometric determinations of V(max) indicated reductions (p < 0.05) in type I at 3 days (-27%) and at 6 days (-34%) and in type IIA fibres at 6 days (-17%). It is concluded that in response to aerobic-based training, sarcoplasmic reticulum Ca²âº-cycling potential is reduced by adaptations that occur soon after training onset.