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PubMed2001

Predictors of isotonic exercise in patients with heart failure.

PURPOSE: Study aims were to determine the predictors of isotonic resistance exercise performance in patients with advanced heart failure and to compare the preexercise values of patients who experienced a negative physiologic response to resistance exercise with those who had minimal or no response. METHODS: A correlational design was used. After pharmacologic left ventricular unloading therapy using a pulmonary artery catheter, 34 patients with advanced heart failure performed graduated isotonic weight-lifting exercises. Measurements were made of hemodynamics and rating of perceived exertion after each test. RESULTS: The following variables, measured at baseline, were significantly correlated with the amount of weight patients were able to lift: rating of perceived exertion (RPE; r = -0.42, P = 0.014); diastolic blood pressure (DBP; r = 0.49, P = 0.03); systolic blood pressure (SBP; r = 0.40, P = 0.017); pulmonary capillary wedge pressure (PCWP; r = 0.39, P = 0.026); and right atrial pressure (RAP; r = 0.35, P = 0.041). Multiple regression analysis, using a stepwise procedure, showed that 47% of the variance in exercise performance was explained by DBP, RPE, and PCWP. There were no significant differences in baseline hemodynamics, ejection fraction, or age between the group of patients who had a negative hemodynamic response at peak exercise and the group of patients who had minimal or no response. CONCLUSIONS: Resting PCWP, DBP, and RPE can provide important information to help clinicians predict isotonic resistance exercise performance in patients with advanced heart failure. However, those patients who have a negative response to this type of exercise cannot be distinguished at baseline by clinical characteristics or age.

Adult↗
PubMed2006

Trunk muscle strength is a strong predictor of bone loss in postmenopausal women.

UNLABELLED: To clarify whether trunk muscle strength and self-reported exercise habits predict subsequent bone loss in healthy post- menopausal women, we examined 143 community-dwelling ambulatory postmenopausal Japanese women (age: 59.9 +/- 6.5 years) without any diseases affecting bone metabolism at baseline, and followed 109 of the 143 subjects for 4 years. Bone mineral density at baseline and at followup was measured at the spine by DEXA to determine the annual change in bone mineral density during the followup. Subjects who lost bone mineral density at an annual rate exceeding -1.78% (1 standard deviation below the mean rate) were defined as rapid bone losers. The isokinetic concentric and eccentric peak torques of the trunk flexors and extensors were measured at baseline. The exercise habits of the subjects were evaluated through detailed interviews. The eccentric trunk flexor and extensor torques were found to correlate with a positive dose-dependent effect on change in bone mineral density while exercise habits showed no correlation. The lower tertile group for the extensor torque showed a ten-fold greater risk for rapid bone loss compared with the upper tertile group. Postmenopausal women with decreased trunk muscle torque may be at increased risk for osteoporosis and should be a target group for preventive measures. LEVEL OF EVIDENCE: Prognostic study, level II (prospective study). See the Guidelines for Authors for a complete description of the levels of evidence.

Absorptiometry, Photon↗
PubMed2003

Derecruitment of the lumbar musculature with fatiguing trunk extension exercise.

STUDY DESIGN: This was a descriptive study involving 20 healthy individuals. OBJECTIVES: To evaluate the neuromuscular activation patterns of the lumbar paraspinal and hip extensor muscles during isotonic trunk extension exercise. SUMMARY OF BACKGROUND DATA: Few studies have evaluated the effect of muscle fatigue on the lumbar musculature during isotonic exercise. METHODS: Electromyographic activity was recorded continuously from the lumbar paraspinal, gluteus maximus, and biceps femoris muscles during isotonic trunk extension exercise performed to muscular failure. Root mean squared electromyography was determined over the concentric portion of each repetition, and polynomial regression analysis was used to describe the association between fatigue and the recruitment patterns. RESULTS: The lumbar paraspinals demonstrated an increase in the electromyogram signal up to 57.9% of maximal fatigue, at which point decrements in electromyography were observed (lumbar [quadratic curve] R2 = 0.0807, SEE = 0.228; beta2 = -8.245(-5)) (P < 0.000). Associated with fatigue, the gluteus maximus demonstrated an increase in electromyography, with an exponential breakpoint occurring at 35.9% of maximal fatigue (gluteus maximus [quadratic curve]: R2 = 0.5059, SEE = 0.865; beta2 = 0.00017) (P = 0.014). The biceps femoris demonstrated a linear increase in electromyography with fatigue (R2 = 0.4667, SEE = 0.284; beta2 = 0.0091) (P < 0.000). To further investigate the derecruitment of the lumbar extensors associated with fatigue, study participants were analyzed individually with regression analyses. Results revealed that the majority of study participants (68.5%) demonstrated a significant decrease (quadratic bend) in lumbar electromyography, with decrements in muscle activity beginning at 53% of maximum. CONCLUSION: During fatiguing trunk extension exercise, an increase in the lumbar paraspinal electromyogram signal occurs up to approximately 55% of maximum fatigue, at which point a decrease in electromyography is observed. Associated with this derecruitment is a concomitant increase in hip extensor muscle activity, suggesting that as the lumbar musculature becomes fatigued, these muscles allow for continuation of the exercise.

Abdominal Muscles↗
PubMed1999

Electromyogram amplitude estimation with adaptive smoothing window length.

Typical electromyogram (EMG) amplitude estimators use a fixed window length for smoothing the amplitude estimate. When the EMG amplitude is dynamic, previous research suggests that varying the smoothing length as a function of time may improve amplitude estimation. This paper develops optimal time-varying selection of the smoothing window length using a stochastic model of the EMG signal. Optimal selection is a function of the EMG amplitude and its derivatives. Simulation studies, in which EMG amplitude was changed randomly, found that the "best" adaptive filter performed as well as the "best" fixed-length filter. Experimental studies found the advantages of the adaptive processor to be situation dependent. Subjects used real-time EMG amplitude estimates to track a randomly-moving target. Perhaps due to task difficulty, no differences in adaptive versus fixed-length processors were observed when the target speed was fast. When the target speed was slow, the experimental results were consistent with the simulation predictions. When the target moved between two constant levels, the adaptive processor responded rapidly to the target level transitions and had low variance while the target dwelled on a level.

Adolescent↗
PubMed1991

An active feedback system for isotonic studies of smooth muscle.

A feedback system used to perform isotonic studies of smooth muscle is presented. This system is capable of applying a constant force to muscle samples regardless of their contractile activities. The force applied to the tissue is controlled using a proportional integral control system that drives a linear motor. The device is integrated into a sucrose gap tissue bath apparatus where measurements of displacement and electrical activity are also possible. The frequency of canine colonic smooth-muscle electrical oscillations is positively related to applied force.

Animals↗
PubMed2000

Study of the control strategy of the quadriceps muscles in anterior knee pain.

Anterior knee pain (AKP) is a common pathological condition, particularly among young people and athletes, associated to an abnormal motion of the patella during the bending of the knee and possibly dependent on a muscular or structural imbalance. A lack of synergy in the quadriceps muscles results in a dynamic misalignment of the patella, which in turn produces pain. AKP rehabilitative therapy consists of conservative treatment whose main objective is to strengthen the Vastus Medialis. The aim of this article is to study the quadriceps muscle control strategy in AKP patients during an isokinetic exercise. Analysis of the muscle activation strategy is important for an objective measurement of the knee functionality in that it helps to diagnose and monitor the rehabilitative treatment. Surface electromyography (EMG) from the three superficial muscles of the femoral quadriceps during a concentric isokinetic exercise has been analyzed along with the signals of knee joint position and torque. A group of 12 AKP patients has been compared with a group of 30 normal subjects. Analysis of the grand ensemble average of the EMG linear envelopes in AKP patients reveals significant modifications in Vastus Medialis activity compared to the other quadriceps muscles. In order to study the synergy of the muscles, temporal identifiers have been associated to the EMG linear envelopes. To this end, EMG linear envelope decomposition in Gaussian pulses turned out to be effective and the results highlight an appreciable delay in the activation of the Vastus Medialis in AKP patients. This muscular unbalance can explain the abnormal motion of the patella.

Adolescent↗
PubMed1984

The role of the free-way space in the generation of muscle pain among denture-wearers.

Although the myofascial pain dysfunction syndrome has a multiple aetiology, faulty vertical dimension is a frequent cause of muscular pain among wearers of full dentures. Furthermore, it has been found that the restoration of a physiological free-way space in such cases, using a method which is based upon cephalometric analysis of the gonial angle, often leads to a dramatic remission of pain. The present investigation was prompted by curiosity as to what the underlying algogenic mechanisms in these cases might be; and how a change in the vertical dimension should so modify them as to result in the disappearance of the pain symptoms. The study is necessarily of a speculative nature, and makes use of two representative cases, one of which was adjudged to have too little free-way, and the other too much. Principles of neuromuscular physiology are applied in attempting to explain the clinical phenomena involved, as well as to find a reason for certain electro-myographic artefacts noted in one of the cases, which would appear to call into question the notion that muscular hyperactivity, per se, is responsible for muscular pain. Potgieter, Monteith & Kemp (1983) have presented an hypothesis that the amount of free-way space present in an individual is an expression of the contractile power of the masseter and medial pterygoid muscles. They have also devised a method whereby, through cephalometric analysis, the optimal amount of free-way may be determined for an edentulous patient during denture construction. Furthermore, they have stated that their method has proved particularly effective in the treatment of denture-wearers presenting with symptoms of the myofascial pain dysfunction syndrome. However, in the light of this syndrome's multifactorial aetiology one must assume that only those symptoms which are related to a faulty free-way space are at issue. The purpose of the present investigation is to examine the latter assertion; and by the application of the suggested method of cephalometric analysis to two representative cases, attempt to explain the phenomenon in terms of neuromuscular mechanisms. Of the two cases to be examined, one was found to have too much free-way, while the other had been provided with too little. Both had presented with symptoms of severe muscle pain.

Adult↗
PubMed2006

Achalasia: physiology and etiopathogenesis.

Achalasia is a disorder of esophageal motility that has been well documented for over 300 years. Despite this, the initiating factor or factors and the underlying mechanisms leading to the characteristic features of achalasia, the absence of distal esophageal peristalsis and abnormal lower esophageal sphincter relaxation, are still not well understood. Recent work has shed light on changes in neurotransmission and cell signaling in the lower esophagus and lower esophageal sphincter that lead to achalasia. A number of recent reviews have thoroughly discussed diagnostic and therapeutic modalities and the reader is referred to these for in-depth review of these topics. The focus of this review will be on our current understanding of the physiology of esophageal peristalsis and lower esophageal sphincter function as it relates to achalasia and on available evidence for etiology and proposed pathophysiologic mechanisms.

Animals↗
PubMed1995

Study of NO and VIP as non-adrenergic non-cholinergic neurotransmitters in the pig gastric fundus.

1. The contribution of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) to non-adrenergic non-cholinergic (NANC) relaxations in the pig gastric fundus was investigated. 2. Circular and longitudinal muscle strips were mounted for isotonic registration in the presence of atropine and guanethidine; tone was raised with 5-hydroxytryptamine. Electrical field stimulation with 10 s trains at 5 min intervals induced responses were abolished by tetrodotoxin. 3. The short-lasting as well as the sustained electrically induced NANC relaxations were significantly reduced by NG-nitro-L-arginine methyl ester (L-NAME). Pretreatment with L-arginine but not D-arginine, prevented the inhibitory effect of L-NAME except for sustained relaxations in the longitudinal muscle strips. 4. Sodium nitroprusside, forskolin, zaprinast and 3-isobutyl-l-methylxanthine induced concentration-dependent relaxations. Exogenous NO mimicked the short-lasting electrically induced relaxations, while endogenous VIP evoked sustained relaxations. The responses to exogenous NO and VIP were not influenced by tetrodotoxin and L-NAME. 5. alpha-Chymotrypsin abolished the responses to exogenous VIP but only moderately reduced NANC relaxations induced by continuous electrical stimulation. Zaprinast potentiated the relaxant responses to sodium nitroprusside and increased the duration of the NANC relaxations induced by electrical stimulation with 10 s trains in circular muscle strips but not in longitudinal muscle strips. 6. The cyclic GMP and cyclic AMP response to electrical stimulation, NO and VIP was measured in circular muscle strips. Short-lasting as well as sustained electrical field stimulation induced an approximately 1.5 fold increase in cyclic GMP content, while NO induced nearly a 40 fold increase. An increase in cyclic AMP content was obtained only with sustained electrical field stimulation. 7. Immunocytochemistry for NO synthase (NOS) revealed immunoreactive neuronal cell bodies in the submucous and myenteric plexuses and nerve fibres in both the circular and longitudinal muscle layer; double-labelling for NOS and VIP showed that VIP coexists in a major part of the intrinsic neurones. NADPH diaphorase-histochemistry showed the same pattern of nitrergic neurones and nerves as NOS-immunocytochemistry. 8. It is concluded that a cyclic GMP- and a cyclic AMP-dependent pathway for relaxation is present in both the circular and longitudinal muscle layer of the pig gastric fundus. NO appears to contribute to short-lasting as well as sustained NANC relaxations. A peptide, possibly VIP, may be involved during sustained stimulation at lower frequencies of stimulation.

Animals↗
PubMed1980

Responses of systemic vascular smooth muscle to hypoxia.

The rapidity and extent of hypoxic relaxation of vascular smooth muscle (VSM) from different systemic vessels is relevant to the study of mechanisms of vasodilation in different vascular beds. Variations between sites may also assist understanding of the link between oxygen tension and mechanical activity, which has been shown not to be a simple deprivation of aerobic processes. Strips of rat portal vein (RPV), rabbit ear artery (REA) and rabbit common carotid artery (RCC) were studied under isotonic conditions, contracted by 10(-6) noradrenaline (NA). Reduction of Po2 to less than 3KPa during NA constraction led to relaxation which was rapid and 90% complete in RPV, rapid and 60% in REA: the relaxation began when tissue Po2 was decreasing and was not lower than 5.5 K Pa. RCC responded slowly and only some strips relaxed. The rapidity and magnitude of relaxation for each type of vessel was comparable to that produced by removal of external calcium. Also for any one type of VSM the response to NA was abolished or diminished to a similar extent by preliminary exposure to hypoxia, or by preliminary removal of calcium. Preliminary hypoxia diminished 50 mmol.1(-1) K+ contractions as much as it diminished NA contractions. Preliminary 1-2 hour exposure to hyperoxia diminished the subsequent relaxant effect of hypoxia. Inhibition of glycolysis (iodoacetic acid) had no effect on normoxic NA contraction or on hypoxic relaxation, but prevented or diminished the subsequent recovery on reoxygenation. Low oxygen tension appears to act in VSM as though it interferes with net influx or utilisation of external calcium.

Animals↗
PubMed1989

The force-velocity relationship at high shortening velocities in the soleus muscle of the rat.

1. In intact skeletal muscle fibres, estimates of unloaded shortening velocity obtained from slack test measurements (V0) have been shown to exceed, by approximately 7%, estimates obtained from extrapolation of velocities measured during isotonic releases (Vmax). In contrast, published values for the V0 of whole soleus muscles of rats exceed Vmax by 56%. In the present study, we tested the hypothesis that this difference between whole muscles and single fibres is due to a difference in their respective force-velocity relationships at loads less than 5% of maximum isometric tetanic force (P0). In addition, we examined, by computer simulation, the effect of inter-fibre heterogeneity on the force-velocity characteristics of a whole muscle. 2. The force-velocity relationship of soleus muscles of rats was determined at low loads, in vitro at 20 degrees C, by recording force maintained during controlled shortening at constant velocities. The relationship was simulated by assigning a hyperbolic force-velocity curve to each motor unit and summing the force contributions of individual units at each of a series of velocities. 3. When measurements from low loads were included, the force-velocity relationship intersected the velocity axis at V0 (5.0 +/- 0.1 fibre lengths/s, mean +/- S.E.M., n = 10), not Vmax (3.1 +/- 0.1 fibre lengths/s). The simulated and measured force-velocity relationships agreed at all loads, supporting the premise that the deviation from hyperbolic form responsible for the large disparity between V0 and Vmax of whole muscles is a consequence of heterogeneity in shortening velocity among fibres.

Animals↗
PubMed2002

Isotonic force modulates force redevelopment rate of intact frog muscle fibres: evidence for cross-bridge induced thin filament activation.

We tested the hypothesis that force-velocity history modulates thin filament activation, as assessed by the rate of force redevelopment after shortening (+dF/dt(R)). The influence of isotonic force on +dF/dt(R) was assessed by imposing uniform amplitude (2.55 to 2.15 microm sarcomere(-1)) but different speed releases to intact frog muscle fibres during fused tetani. Each release consisted of a contiguous ramp- and step-change in length. Ramp speed was changed from release to release to vary fibre shortening speed from 1.00 (2.76 +/- 0.11 microm half-sarcomere(-1) s(-1)) to 0.30 of maximum unloaded shortening velocity (V(u)), thereby modulating isotonic force from 0 to 0.34 F(o), respectively. The step zeroed force and allowed the fibre to shorten unloaded for a brief period of time prior to force redevelopment. Although peak force redevelopment after different releases was similar, +dF/dt(R) increased by 81 +/- 6 % (P < 0.05) as fibre shortening speed was reduced from 1.00 V(u). The +dF/dt(R) after different releases was strongly correlated with the preceding isotonic force (r = 0.99, P < 0.001). Results from additional experiments showed that the slope of slack test plots produced by systematically increasing the step size that followed each ramp were similar. Thus, isotonic force did not influence V(u) (mean: 2.84 +/- 0.10 microm half-sarcomere(-1) s(-1), P < 0.05). We conclude that isotonic force modulates +dF/dt(R) independent of change in V(u), an outcome consistent with a cooperative influence of attached cross-bridges on thin filament activation that increases cross-bridge attachment rate without alteration to cross-bridge detachment rate.

Actins↗
PubMed2004

Human single muscle fibre function with 84 day bed-rest and resistance exercise.

Muscle biopsies were obtained from the vastus lateralis before and after 84 days of bed-rest from six control (BR) and six resistance-exercised (BRE) men to examine slow- and fast-twitch muscle fibre contractile function. BR did not exercise during bed-rest and had a 17 and 40% decrease in whole muscle size and function, respectively. The BRE group performed four sets of seven maximal concentric and eccentric supine squats 2-3 days per week (every third day) that maintained whole muscle strength and size. Slow (MHC I) and fast (MHC IIa) muscle fibres were studied at 15 degrees C for diameter, peak force (P(o)), contractile velocity (V(o)) and force-power parameters. SDS-PAGE was performed on each single fibre after the functional experiments to determine MHC isoform composition. MHC I and IIa BR fibres were, respectively, 15 and 8% smaller, 46 and 25% weaker (P(o)), 21 and 6% slower (V(o)), and 54 and 24% less powerful after bed-rest (P < 0.05). BR MHC I and IIa P(o) and power normalized to cell size were lower (P < 0.05). BRE MHC I fibres showed no change in size or V(o) after bed-rest; however, P(o) was 19% lower (P < 0.05), resulting in 20 and 30% declines (P < 0.05) in normalized P(o) and power, respectively. BRE MHC IIa fibres showed no change in size, P(o) and power after bed-rest, while V(o) was elevated 13% (P < 0.05). BRE MHC IIa normalized P(o) and power were 10 and 15% lower (P < 0.05), respectively. MHC isoform composition shifted away from MHC I fibres, resulting in an increase (P < 0.05) in MHC I/IIa (BR and BRE) and MHC IIa/IIx (BR only) fibres. These data show that the contractile function of the MHC I fibres was more affected by bed-rest and less influenced by the resistance exercise protocol than the MHC IIa fibres. Considering the large differences in power of human MHC I and IIa muscle fibres (5- to 6-fold), the maintenance of whole muscle function with the resistance exercise programme is probably explained by (1). the maintenance of MHC IIa power and (2). the shift from slow to fast (MHC I --> MHC I/IIa) in single fibre MHC isoform composition.

Adult↗
PubMed1988

Caffeine, maximal power output and fatigue.

The purpose of this investigation was to determine the effects of caffeine ingestion on maximal power output and fatigue during short term, high intensity exercise. Nine adult males performed 15 s maximal exercise bouts 60 min after ingestion of caffeine (7 mg.kg-1) or placebo. Exercise bouts were carried out on a modified cycle ergometer which allowed power output to be computed for each one-half pedal stroke via microcomputer. Peak power output under caffeine conditions was not significantly different from that obtained following placebo ingestion. Similarly, time to peak power, total work, power fatigue index and power fatigue rate did not differ significantly between caffeine and placebo conditions. These results suggest that caffeine ingestion does not increase one's maximal ability to generate power. Further, caffeine does not alter the rate or magnitude of fatigue during high intensity, dynamic exercise.

Adult↗
PubMed1994

Resistance exercise decreases beta-endorphin immunoreactivity.

Previous research investigating the response of plasma beta-endorphins (beta-EP) to resistance exercise has resulted in equivocal findings. To examine further the effects of resistance exercise on beta-EP immunoreactivity, 10 male and 10 female college-age students participated in a series of controlled isotonic resistance exercises. The session consisted of three sets of eight repetitions at 80% of one repetition maximum (1-RM) for each of the following exercises: (1) bench press; (2) lateral pull-downs; (3) seated arm curls; and (4) military press. Blood plasma was sampled both before and after the lifting routine and beta-endorphin levels were determined by radioimmunoassay. A Students t test for paired samples indicated that mean(s.e.) plasma beta-endorphin levels after exercise (10.5(1.3) pg beta-EP ml-1) were significantly decreased as compared with pre-exercise (control) levels (16.5(1.2), P < 0.05). While the mechanism(s) contributing to the decrease in immunoreactivity is unclear, it may be the result of the synergistic effect of beta-EP clearance during rest intervals and changes in psychological states between sampling.

Adult↗
PubMed1999

Effect on nasal resistance of an external nasal splint and isotonic exercise.

OBJECTIVES: The now commonplace wearing of external nasal splints by sportsmen and athletes has never been scientifically evaluated. The present study looks into the effect of isotonic exercise on nasal resistance, and examines whether this effect is altered by the wearing of an external nasal splint. METHODS: Twenty subjects not suffering from rhinitis were tested. Nasal resistance measurements were recorded using an anterior rhinomanometer before and after isotonic exercise with and without an external nasal splint. Pulse and blood pressure were measured before and after exercise. RESULTS: Significant changes were observed in pulse (p < 0.001) and both systolic (p < 0.002) and diastolic (p < 0.001) blood pressure in response to exercise. Significant differences were seen in nasal resistance when the splint was applied (p < 0.001) and after exercise (p < 0.003). No significant difference was observed after exercise when the splint was worn (p = 0.167). CONCLUSIONS: External nasal splints decrease nasal resistance at rest but are of little value during isotonic exercise.

Airway Resistance↗
PubMed2003

Progressive decrease of intramyocellular accumulation of H+ and Pi in human skeletal muscle during repeated isotonic exercise.

The purpose of this study was to evaluate the hypotheses that accumulation of hydrogen ions and/or inorganic phosphate (Pi) in skeletal muscle increases with repeated bouts of isotonic exercise. (31)P-Magnetic resonance spectroscopy was used to examine the gastrocnemius muscle of seven highly aerobically trained females during four bouts of isotonic plantar flexion. The exercise bouts (EX1-4) of 3 min and 18 s were separated by 3 min and 54 s of complete rest. Muscle ATP did not change during the four bouts. Phosphocreatine (PCr) degradation during EX1 (13.3 +/- 2.4 mmol/kg wet weight) was higher (P < 0.01) compared with EX3-4 (9.7 +/- 1.6 and 9.6 +/- 1.8 mmol/kg wet weight, respectively). The intramyocellular pH at the end of EX1 (6.87 +/- 0.05) was significantly lower (P < 0.001) than those of EX2 (6.97 +/- 0.02), EX3 (7.02 +/- 0.01), and EX4 (7.02 +/- 0.02). Total Pi and diprotonated Pi were significantly higher (P < 0.001) at the end of EX1 (17.3 +/- 2.7 and 7.8 +/- 1.6 mmol/kg wet weight, respectively) compared with the values at the end of EX3 and EX4. The monoprotonated Pi at the end of EX1 (9.5 +/- 1.2 mmol/kg wet weight) was also significantly higher (P < 0.001) than that after EX4 (7.5 +/- 1.1 mmol/kg wet weight). Subjects' rating of perceived exertion increased (P < 0.001) toward exhaustion as the number of exercises progressed (7.1 +/- 0.4, EX1; 8.0 +/- 0.3, EX2; 8.5 +/- 0.3, EX3; and 9.0 +/- 0.4, EX4; scale from 0 to 10). The present results indicate that human muscle fatigue during repeated intense isotonic exercise is not due to progressive depletion of high energy phosphates nor to intracellular accumulation of hydrogen ions, total, mono-, or diprotonated Pi.

Adenosine Triphosphate↗
PubMed2001

Resistance training improves single muscle fiber contractile function in older women.

The purpose of this study was to 1) examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older women (n = 7; 74 +/- 2 yr) and 2) to compare these results to our previously completed single cell PRT work with older men (n = 7; 74 +/- 2 yr) (Trappe S, Williamson D, Godard M, Porter D, Rowden G, and Costill D. J Applied Physiol 89:143--152, 2000). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsies were obtained from the vastus lateralis before and after the PRT. Chemically skinned single muscle fibers (n = 313) were studied at 15 degrees C for peak tension (P(o)), unloaded shortening velocity (V(o)), and power. Due to the low number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 24% (90 +/- 2 to 112 +/- 6 microm; P < 0.05) in MHC I fibers with no change in MHC IIa fibers. P(o) increased (P < 0.05) 33% in MHC I (0.76 +/- 0.04 to 1.01 +/- 0.09 mN) and 14% in MHC IIa (0.73 +/- 0.04 to 0.83 +/- 0.05 mN) fibers. Muscle fiber V(o) was unaltered in both fiber types with PRT. MHC I and IIa fiber power increased (P < 0.05) 50% [11 +/- 2 to 17 +/- 2 microN. fiber length (FL). s(-1)] and 25% (40 +/- 8 to 51 +/- 6 microN. FL. s(-1)), respectively. However, when peak power was normalized to cell size, no pre- to postimprovements were observed. These data indicate that PRT in elderly women increases muscle cell size, strength, and peak power in both slow and fast muscle fibers, which was similar to the older men. However, in contrast to the older men, no change in fiber V(o) or normalized power was observed in the older women. These data suggest that older men and women respond differently at the muscle cell level to the same resistance-training stimulus.

Aged↗