Mary P. Miles

Neuromuscular dysfunction following eccentric exercise.

This study examined the effects of exercise-induced muscle damage on tremor and proprioception components of neuromuscular function. Six male and six female volunteers (aged 18-30 yr) performed 50 maximal eccentric muscle actions using the forearm flexors of the nondominant arm. Forearm flexor tremor and perception of voluntary force and joint position were monitored to assess changes in neuromuscular function. Data were analyzed using REANOVA. Serum creatine kinase activity increased from a baseline value of 68 +/- 13 IU.l-1 to 2849 +/- 852 IU.l-1 5 d after exercise (P < 0.05). This was accompanied by prolonged impaired joint range of motion (P < 0.01) and reduced maximum strength (P < 0.01). Muscle soreness peaked 3 d postexercise (P < 0.01; Wilcoxon test). Tremor amplitude was increased (P < 0.01) until 48 h after exercise, whereas the power frequency spectrum was unaffected. Perception of joint position at elbow angles of 1.57 rad (P < 0.01) and 2.09 rad (P < 0.05) and perception of force (P < 0.01) were significantly impaired when the control arm acted as the reference. Joint positions were more accurately reproduced when the experimental arm acted as its own reference. The increase in tremor amplitude and loss of proprioceptive function in the days after damage-inducing eccentric exercise suggest significant impairment of neuromuscular function.

Effect of resistance training on women's strength/power and occupational performances.

PURPOSE The effects of resistance training programs on strength, power, and military occupational task performances in women were examined. METHODS Untrained women aged (mean +/- SD) 23 +/- 4 yr were matched and randomly placed in total- (TP, N = 17 and TH, N = 18) or upper-body resistance training (UP, N = 18 and UH, N = 15), field (FLD, N = 14), or aerobic training groups (AER, N = 11). Two periodized resistance training programs (with supplemental aerobic training) emphasized explosive exercise movements using 3- to 8-RM training loads (TP, UP), whereas the other two emphasized slower exercise movements using 8- to 12-RM loads (TH, UH). The FLD group performed plyometric and partner exercises. Subjects were tested for body composition, strength, power, endurance, maximal and repetitive box lift, 2-mile loaded run, and U.S. Army Physical Fitness Tests before (T0) and after 3 (T3) and 6 months of training (T6). For comparison, untrained men (N = 100) (MEN) were tested once. RESULTS Specific training programs resulted in significant increases in body mass (TP), 1-RM squat (TP, TH, FLD), bench press (all except AER), high pull (TP), squat jump (TP, TH, FLD), bench throw (all except AER), squat endurance (all except AER), 1-RM box lift (all except aerobic), repetitive box lift (all), push-ups (all except AER), sit-ups (all except AER), and 2-mile run (all). CONCLUSIONS Strength training improved physical performances of women over 6 months and adaptations in strength, power, and endurance were specific to the subtle differences (e.g., exercise choice and speeds of exercise movement) in the resistance training programs (strength/power vs strength/hypertrophy). Upper- and total-body resistance training resulted in similar improvements in occupational task performances, especially in tasks that involved upper-body musculature. Finally, gender differences in physical performance measures were reduced after resistance training in women, which underscores the importance of such training for physically demanding occupations.

Cytokine production by stimulated mononuclear cells did not change with aging in apparently healthy, well-nourished women

Aging is often associated with a dysregulation of the immune system. We examined mitogen-stimulated production of interleukin (IL)-2 and proinflammatory cytokines, IL-1beta and IL-6, in apparently healthy and generally well-nourished old versus young women. Subjects were screened for health using the SENIEUR protocol and a panel of laboratory tests for inflammation, as well as for the adequacy of nutritional status using criteria related to undernutrition, and protein, iron, vitamin B(12), and folate status. Young (n=26, age: 20-40 years) and old (n=44, age: 62-88 years) cohorts did not differ on the number of circulating monocytes, granulocytes, B (CD19+) cells, and T (CD3+, CD4+, and CD8+) cells. No differences (P>0.10) were seen between the two age groups in IL-2, IL-1beta and IL-6 levels in whole blood cultures at 48 h after stimulation with PHA (5 mg/l). Furthermore, no age-related differences were noted in the absolute amounts (pg) of IL-1beta and IL-6 after normalizing for circulating monocytes, B cells, or T cells (P>0.10). Similarly, no age-related decline in absolute amount of IL-2 (pg) after normalizing for circulating T cells was noted (P>0.10). Thus, contrary to most previous reports, our results do not support an increase in the production of proinflammatory cytokines IL-1beta and IL-6, and a reduced production of IL-2 with aging when health and nutritional status are maintained. These findings support our previous results of no change in monocyte function and few alterations in acquired immune response in a carefully selected group of healthy and well-nourished elderly women.

Muscle function at the wrist following 9 d of immobilization and suspension

The purpose of this study was to evaluate the effects of 9 d of immobilization and partial suspension on muscle function at the wrist. Twelve female subjects (19-27 yr) wore a cast suspended from the neck by a sling that immobilized muscles acting on the wrist. Atrophy, muscle damage indicators, isometric and isokinetic strength, reaction time, speed of movement, and fatigability were assessed. Forearm muscle cross-sectional area decreased by 4.1% following immobilization and suspension. There was no indication that significant muscle degeneration occurred during immobilization or when muscles resumed normal function. Isometric strength for flexion and extension decreased by 29.3 and 32.5%, respectively. Concentric strength decrements for flexion, extension, pronation, and supination ranged from 8.9-21.7% at 2.11 and 3.16 rad.s-1. Eccentric strength decrements at 2.11 rad.s-1 for the same movements ranged from 12.5-18.5%. Fatigability was unaffected. Greater relative strength losses compared to decreased muscle cross-sectional area may be the result of a decrease in contractile protein density or unidentified neural factors following immobilization and partial suspension. However, neuromuscular control of reaction time was not affected.

Immune function did not decline with aging in apparently healthy, well-nourished women.

Nutrition plays a crucial role in immune function. Most studies on age-associated changes in immunocompetence in healthy adults did not examine the nutritional status of participants extensively. Inadequate nutritional status may confound the relationship of aging and immune response. The purpose of this study was to examine age-related changes in parameters of acquired and innate immunity in healthy and generally well-nourished older (62-88 years) versus younger (20-40 years) women. Subjects were screened for participation using the health criteria of the SENIEUR protocol as well as a number of nutrition criteria related to undernutrition, and protein, iron, vitamin B12, and folate status. Young and old women did not differ in total T (CD3+), T-helper (CD4+), or T-cytotoxic (CD8+) cell number. However, older women tended to have lower T-cell proliferation response to concanavalin A (P < 0.10) and significantly reduced response to phytohemagglutinin (P < 0.05). No age-related changes were noted in natural killer cell number or cytotoxicity. Phagocytosis and subsequent oxidative burst activity also did not differ between young and old women. Most immune parameters were not compromised with aging in this cohort of apparently healthy, well-nourished women. These findings highlight the importance of simultaneous examination of health and nutritional status in studies of immune function with aging.

Neuromuscular control following maximal eccentric exercise

Abstract Kinematic and electromyographic (EMG) analysis of a target-directed, maximal velocity movement was used to investigate the effects of high-force eccentric exercise on the neuromuscular control of elbow flexion. Ten non-weight-trained females [19.6 (1.6) years old] performed 50 maximal velocity elbow flexion movements from 0 to 1.58 rad (90°), as rapidly as possible in response to a light stimulus, while kinematic and triphasic EMG parameters were measured. This was done three times pre-exercise, immediately and 1, 2, 3, 4, and 5 days following the 50 maximal eccentric elbow flexion actions. The eccentric exercise caused lengthening of kinematic parameters including total movement time and time to peak velocity. The EMG elements of the biceps brachii (b.) motor time, time to peak EMG, biceps b. burst duration, and the latency period between biceps b. and triceps b. bursts were lengthened post-exercise. These changes persisted for up to 5 days post-exercise. The exercise also caused a large increase in serum creatine kinase (CK) activity. It was concluded that high-force eccentric exercise in this population caused prolonged changes in neuromuscular control that were a function of exercise-induced disruption of the skeletal muscle. Compensation in the central motor program was such that the components of the triphasic EMG pattern were systematically lengthened.

Creatine supplementation does not reduce muscle damage or enhance recovery from resistance exercise.

Previous studies have shown that creatine supplementation reduces muscle damage and inflammation following running but not following high-force, eccentric exercise. Although the mechanical strain placed on muscle fibers during high-force, eccentric exercise may be too overwhelming for creatine to exert any protective effect, creatine supplementation may protect skeletal muscle stressed by a resistance training challenge that is more hypoxic in nature. The purpose of this study was to examine the effects of short-term creatine supplementation on markers of muscle damage (i.e., strength, range of motion, muscle soreness, muscle serum protein activity, C-reactive protein) to determine whether creatine supplementation offers protective effects on skeletal muscle following a hypoxic resistance exercise test. Twenty-two healthy, weight-trained men (19-27 years) ingested either creatine or a placebo for 10 days. Following 5 days of supplementation, subjects performed a squat exercise protocol (5 sets of 15-20 repetitions at 50% of 1 repetition maximum [1RM]). Assessments of creatine kinase (CK) and lactate dehydrogenase activity, high-sensitivity C-reactive protein, maximal strength, range of motion (ROM), and muscle soreness (SOR) with movement and palpation were conducted pre-exercise and during a 5-day follow up. Following the exercise test, maximal strength and ROM decreased, whereas SOR and CK increased. Creatine and placebo-supplemented subjects experienced significant decreases in maximal strength (creatine: 13.4 kg, placebo: 17.5 kg) and ROM (creatine: 2.4 degrees , placebo: 3.0 degrees ) immediately postexercise, with no difference between groups. Following the exercise test, there were significant increases in SOR with movement and palpation (p < 0.05 at 24, 48, and 72 hours postexercise), and CK activity (p < 0.05 at 24 and 48 hours postexercise), with no differences between groups at any time. These data suggest that oral creatine supplementation does not reduce skeletal muscle damage or enhance recovery following a hypoxic resistance exercise challenge.

Low-dose creatine supplementation enhances fatigue resistance in the absence of weight gain

OBJECTIVE We examined the effects of 6 wk of low-dose creatine supplementation on body composition, muscle function, and body creatine retention. METHODS Twenty healthy men and women (21 ± 2 y old) were randomized to receive creatine (0.03 g · kg(-1) · d(-1); n = 10, 4 women) or placebo (n = 10, 4 women) for 6 wk in a double-blind placebo-controlled fashion. Participants were tested on two occasions before supplementation to establish a reliable baseline, and then were retested after supplementation. Testing included body composition, maximal strength (three-repetition maximal concentric knee extension at 180 degrees/s), muscle fatigue (five sets of 30 concentric knee extensions at 180 degrees/s), and plasma creatine concentration. RESULTS There were no significant differences in body mass, fat-free mass, fat mass, body fat percentage, total body water, or maximal strength in either group from before to after supplementation (all P > 0.05). After supplementation, plasma creatine increased significantly in the creatine group (+182%, P = 0.03), with no difference in the placebo group. Compared with baseline values, creatine-supplemented volunteers were more resistant to fatigue during sets 2 (7%), 3 (9%), 4 (9%), and 5 (11%) (all P < 0.05). In placebo-supplemented participants, there was no improvement in fatigue resistance during sets 2 (0%), 3 (1%), 4 (0%), and 5 (-1%) (all P > 0.05). CONCLUSION Ingesting a low dose (≈2.3 g/d) of creatine for 6 wk significantly increased plasma creatine concentration and enhanced resistance to fatigue during repeated bouts of high-intensity contractions.

Influence of muscle strength and total work on exercise-induced plasma growth hormone isoforms in women

The purpose of this investigation was to determine the influence of physical strength and the ability to do more total work on human growth hormone (GH) variants to a heavy resistance exercise protocol in untrained women. From a distribution of 100 healthy, untrained women, the strongest 10 women (S) and the weakest 10 women (W) were compared for GH responses pre- and post an acute heavy resistance exercise test (AHRET, 6 sets of 10 RM squats, 2 minutes rest between sets). Blood samples were obtained pre-exercise and immediately post-exercise and subsequently analysed in total as well as fractionated by Sephacryl S-100R column chromatography into three molecular weight size classes: fraction A: > 60 kD, fraction B: 30-60 kD, fraction C: < 30 kD. For each total sample as well as each fraction, immunoreactive GH was measured via the Nichols IRMA, while bioactive GH was measured via the hypox rat tibial line bioassay and Diagnostic Systems Laboratorys immunofunctional GH ELISA. No exercise-induced changes or differences between groups were observed in the tibial line bioassay. However, the S group displayed a significantly higher pre-exercise resting value in the total fraction than the W group. Conversely, the W group exhibited a significantly higher pre-exercise value in the smaller molecular weight fraction C. With regards to the immunofunctional and immunoreactive assays, the total fraction, fraction A, and fraction B demonstrated significant (P < or = 0.05) exercise-induced increases in both the S and W group despite no group differences. For the Nichols and immunofunctional assays significant exercise-induced changes were observed in the smaller molecular weight C fraction in the W group but not the S group. However, the S group displayed a significantly higher pre-exercise value in fraction C relative to the W group. These data demonstrate for the first time that differences exist in the GH molecular weight variants between strong and weak untrained women, with the lower molecular weight variants seemingly less responsive to greater amounts of exercise in stronger women, thus suggesting differential regulation of GH molecular weight variants during resistance exercise due to pre-existing physical parameters.

Eccentric exercise augments the cardiovascular response to static exercise

High-force eccentric exercise induces neuromuscular dysfunction and may augment the cardiovascular response to exercise. This investigation sought to determine whether changes in strength and sense of force following high-force eccentric exercise alter heart rate and blood pressure responses during isometric contractions. Subjects (4F,6M) performed 50 maximum resistance eccentric actions with one arm (ECC arm). Contractions at 10% of the ECC arm maximum were held for 7 min on two pre-exercise days. The force output perceived to be the same as 10% of the pre-exercise maximum was determined using a force matching task. This force, 35.6, 27.2, and 21.1% lower on days 1, 3, and 5 post-exercise, was held during isometric contractions on these days, respectively. Despite a lowering of absolute contraction force, heart rate (P < 0.05) and blood pressure (P < 0.001) responses during contractions using the ECC arm were consistently elevated relative to the control arm. However, subjects perceived that they were exerting forces similar to those achieved before eccentric exercise-induced neuromuscular dysfunction. These findings suggest that perceived effort following strength loss induced by mechanically stressful exercise dictates the cardiovascular responses during isometric contractions.