Effects of resistance training on endurance capacity and muscle fiber composition in young top-level cyclists

Equivocal findings exist on the effect of concurrent strength (S) and endurance (E) training on endurance performance and muscle morphology. Further, the influence of concurrent SE training on muscle fiber-type composition, vascularization and endurance capacity remains unknown in top-level endurance athletes. The present study examined the effect of 16 weeks of concurrent SE training on maximal muscle strength (MVC), contractile rate of force development (RFD), muscle fiber morphology and composition, capillarization, aerobic power (VO2max), cycling economy (CE) and long/short-term endurance capacity in young elite competitive cyclists (n=14). MVC and RFD increased 12-20% with SE (P<0.01) but not E. VO2max remained unchanged. CE improved in E to reach values seen in SE. Short-term (5-min) endurance performance increased (3-4%) after SE and E (P<0.05), whereas 45-min endurance capacity increased (8%) with SE only (P<0.05). Type IIA fiber proportions increased and type IIX proportions decreased after SE training (P<0.05) with no change in E. Muscle fiber area and capillarization remained unchanged. In conclusion, concurrent strength/endurance training in young elite competitive cyclists led to an improved 45-min time-trial endurance capacity that was accompanied by an increased proportion of type IIA muscle fibers and gains in MVC and RFD, while capillarization remained unaffected.     

ACE ID genotype and the muscle strength and size response to unilateral resistance training

PURPOSE: To examine associations among the angiotensin I-converting enzyme (ACE) insertion (I)/deletion (D) polymorphism and the response to a 12-wk (2 d.wk) unilateral, upper-arm resistance training (RT) program in the trained (T, nondominant) and untrained (UT, dominant) arms. METHODS: Subjects were 631 (mean+/-SEM, 24.2+/-0.2 yr) white (80%) men (42%) and women (58%). The ACE ID genotype was in Hardy-Weinberg equilibrium with frequencies of 23.1, 46.1, and 30.8% for ACE II, ID, and DD, respectively (chi=1.688, P=0.430). Maximum voluntary contraction (MVC) and one-repetition maximum (1RM) assessed peak elbow flexor muscle strength. Magnetic resonance imaging measured biceps muscle cross-sectional area (CSA). Multiple variable and repeated-measures ANCOVA tested whether muscle strength and size differed at baseline and pre- to post-RT among T and UT and ACE ID genotype. RESULTS: Baseline muscle strength and size were greater in UT than T (P<0.001) and did not differ among ACE ID genotype in either arm (P >or= 0.05). In T, MVC increases were greater for ACE II/ID (22%) than DD (17%) (P<0.05), whereas 1RM (51%) and CSA (19%) gains were not different among ACE ID genotype pre- to post-RT (P >or= 0.05). In UT, MVC increased among ACE II/ID (7%) (P<0.001) but was similar among ACE DD (2%) pre- to post-RT (P >or= 0.05). In UT, 1RM (11%) and CSA (2%) increases were greater for ACE DD/ID than ACE II (1RM, 7%; CSA, -0.1%) (P<0.05). ACE ID genotype explained approximately 1% of the MVC response to RT in T and approximately 2% of MVC, 2% of 1RM, and 4% of CSA response in UT (P<0.05). CONCLUSION: ACE ID genotype is associated with the contralateral effects of unilateral RT, perhaps more so than with the muscle strength and size adaptations that result from RT.     

Whey protein hydrolysate augments tendon and muscle hypertrophy independent of resistance exercise contraction mode

In a comparative study, we investigated the effects of maximal eccentric or concentric resistance training combined with whey protein or placebo on muscle and tendon hypertrophy. 22 subjects were allocated into either a high‐leucine whey protein hydrolysate + carbohydrate group (WHD) or a carbohydrate group (PLA). Subjects completed 12 weeks maximal knee extensor training with one leg using eccentric contractions and the other using concentric contractions. Before and after training cross‐sectional area (CSA) of m. quadriceps and patellar tendon CSA was quantified with magnetic resonance imaging and a isometric strength test was used to assess maximal voluntary contraction (MVC) and rate of force development (RFD). Quadriceps CSA increased by 7.3 ± 1.0% (P < 0.001) in WHD and 3.4 ± 0.8% (P < 0.01) in PLA, with a greater increase in WHD compared to PLA (P < 0.01). Proximal patellar tendon CSA increased by 14.9 ± 3.1% (P < 0.001) and 8.1 ± 3.2% (P = 0.054) for WHD and PLA, respectively, with a greater increase in WHD compared to PLA (P < 0.05), with no effect of contraction mode. MVC and RFD increased by 15.6 ± 3.5% (P < 0.001) and 12–63% (P < 0.05), respectively, with no group or contraction mode effects. In conclusion, high‐leucine whey protein hydrolysate augments muscle and tendon hypertrophy following 12 weeks of resistance training – irrespective of contraction mode.     

Variability in muscle size and strength gain after unilateral resistance training

PURPOSE: This study assessed variability in muscle size and strength changes in a large cohort of men and women after a unilateral resistance training program in the elbow flexors. A secondary purpose was to assess sex differences in size and strength changes after training. METHODS: Five hundred eighty-five subjects (342 women, 243 men) were tested at one of eight study centers. Isometric (MVC) and dynamic strength (one-repetition maximum (1RM)) of the elbow flexor muscles of each arm and magnetic resonance imaging (MRI) of the biceps brachii (to determine cross-sectional area (CSA)) were assessed before and after 12 wk of progressive dynamic resistance training of the nondominant arm. RESULTS: Size changes ranged from -2 to +59% (-0.4 to +13.6 cm), 1RM strength gains ranged from 0 to +250% (0 to +10.2 kg), and MVC changes ranged from -32 to +149% (-15.9 to +52.6 kg). Coefficients of variation were 0.48 and 0.51 for changes in CSA (P = 0.44), 1.07 and 0.89 for changes in MVC (P < 0.01), and 0.55 and 0.59 for changes in CSA (P < 0.01) in men and women, respectively. Men experienced 2.5% greater gains for CSA (P < 0.01) compared with women. Despite greater absolute gains in men, relative increases in strength measures were greater in women versus men (P < 0.05). CONCLUSION: Men and women exhibit wide ranges of response to resistance training, with some subjects showing little to no gain, and others showing profound changes, increasing size by over 10 cm and doubling their strength. Men had only a slight advantage in relative size gains compared with women, whereas women outpaced men considerably in relative gains in strength.     

Explosive heavy-resistance training in old and very old adults: changes in rapid muscle force, strength and power

Age-related decline in muscle power predicts falls, motor impairments and disability. Recent guidelines suggested that training programs should be tailored to maximize muscle power. This study investigated the effects of 12 weeks of explosive-type heavy-resistance training (75-80% of 1 repetition maximum) in old (60-65 years, TG60) and very old (80-89 years, TG80) community-dwelling women. Training was performed with maximal intentional acceleration of the training load during the concentric movement phase. Maximal isometric voluntary muscle strength (MVC), rapid force capacity, assessed as rate of force development (RFD), and impulse, maximal muscle power during a countermovement jump (CMJ) and during unilateral leg extension task (LEP) were evaluated. RFD, impulse and MVC increased by 51%, 42% and 28% in TG80, and by 21%, 18% and 18% in TG60, respectively. CMJ jump height increased by 18% and 10% in TG80 and TG60, respectively, while jump peak power increased in TG60 (5%). Finally, LEP increased 28% in TG80 and 12% in TG60. These findings demonstrate that explosive-type heavy-resistance training seems to be safe and well tolerated in healthy women even in the eighth decade of life and elicits adaptive neuromuscular changes in selected physiological variables that are commonly associated with the risk of falls and disability in aged individuals.     

Changes in muscle strength and morphology after muscle unloading in Special Forces missions

The purpose of the present study was to determine the changes in maximal muscle strength, rapid force capacity, jumping performance and muscle morphology following a Special Forces military operation involving 8 days of muscle unloading. Nine male Special Forces soldiers were tested before (pre) and immediately after (post1) an 8‐day simulated special support and reconnaissance (SSR) mission and after 3 h of active recovery (post2). Maximal muscle strength (MVC) and rate of force development (RFD) were measured along with maximal counter movement jump height (JH). Muscle biopsies were obtained from the vastus lateralis at pre and post1. Acute reductions were found in MVC (11%), JH (10%) and RFD (17–22%) after 8 days of muscle unloading (post1) (P≤0.05). Type IIX fiber type area% increased (P≤0.05) at post1 together with a tendency toward increased type IIX fiber type % (P=0.09) and decreased type I fiber type % (P=0.06), suggesting a transition toward a less fatigue‐resistant fiber‐type profile. In conclusion, short‐term unloading during SSR missions led to marked reductions in mechanical muscle function and functional performance, which may be partly explained by the changes in muscle morphology. Future studies should identify intervention strategies to counter‐act the observed impairments.     

Steadiness training with light loads in the knee extensors of elderly adults

PURPOSE: This study was conducted to determine the effect of steadiness training with light loads in the knee extensors of elderly adults. METHODS: Twenty-one elderly adults (72 +/- 4.6 yr) performed 16 wk of closely supervised knee extensor training that consisted of lifting and lowering 30% of the one-repetition maximum (1-RM) load as steadily as possible (10 reps per set, three sets per session, three sessions per week). Nine subjects served in a control group. Unilateral and bilateral maximal voluntary contraction (MVC) force; 1-RM load; force fluctuations during submaximal isometric, concentric, and eccentric contractions; timed functional performance (gait, chair rise, stair ascent and descent); muscle volume via magnetic resonance imaging (MRI); and the electromyogram (EMG) were measured. RESULTS: The training group exhibited modest average gains in MVC force and 1-RM load; muscle volume and EMG were unaltered. Although isometric steadiness was unchanged on average, training elicited the greatest improvements in the least steady subjects. Force fluctuations during concentric and eccentric contractions were significantly reduced. Of 21 subjects, 14 responded to training with gains in 1-RM load greater than the typical change (6%) in the control group. Before training, these responders exhibited greater force during bilateral compared with unilateral contractions. The small changes in physical functional performance were similar for the training and control groups. The training group could lift the pretraining 1-RM load 4.6 times after training (5.6 times for responders). CONCLUSIONS: Steadiness training with the knee extensors thus produced neural adaptations that increased strength in elderly adults who exhibited bilateral facilitation, improved isometric steadiness in unsteady subjects, improved steadiness during concentric and eccentric contractions, and enhanced the ability to lift heavy loads repeatedly.     

Functional adaptability of muscle fibers to long-term resistance exercise

PURPOSE: We compared the functional properties of muscle fibers from two groups of subjects that differed widely in their training history to investigate whether long-term resistance exercise alters the intrinsic contractile properties of skeletal muscle fibers. METHODS: Vastus lateralis muscle biopsies were obtained from six sedentary males (NT group, age = 23 +/- 1 yr) and six males who had participated in regular resistance exercise training over the preceding 7.6 +/- 1.6 yr (RT group, 22 +/- 1 yr). Chemically skinned muscle fiber segments were activated with a saturating free [Ca2+] to quantify fiber peak Ca2+-activated force (P(o)), unloaded shortening velocity (V(o)), and peak power. Fiber segment myosin heavy chain (MHC) isoform content was identified by gel electrophoresis. RESULTS: Slow and fast fibers from the RT group were larger in CSA and produced greater absolute P(o) and absolute peak power in comparison with fibers from the NT group. However, these differences were no longer evident after P(o) and peak power were normalized to fiber CSA and fiber volume, respectively. V(o)/fiber length was dependent on fiber MHC content but independent of training status. CONCLUSION: Fiber hypertrophy was sufficient to account for intergroup differences in P(o) and peak power of slow and fast fibers. There was no evidence that the intrinsic contractility of slow or fast fibers, as evaluated by force, shortening velocity, and power normalized to the appropriate fiber dimensions, differed between RT and NT groups.     

Aging, visuomotor correction, and force fluctuations in large muscles

PURPOSE: To determine the contribution of visuomotor correction to increased force fluctuations in the elbow flexor and knee extensor muscles of elderly adults. METHODS: Young (N = 22, 23 +/- 3 yr) and elderly (N = 23, 74 +/- 7 yr) adults performed constant-force contractions at target forces of 2.5, 30, and 65% MVC. Visual feedback was provided (6-8 s) and then removed (6-8 s). After removal of drift (< 0.5 Hz) from the force, the standard deviation (SD) and coefficient of variation (CV) of force were calculated from vision and no-vision data. RESULTS: Maximal voluntary contraction (MVC) force was 19% lower for elbow flexors and 37% lower for knee extensors in elderly adults than in young adults. Overall, the CV of force was 27% greater in the vision condition compared with the no-vision condition. The CV of force for vision was greater for elderly adults than for young adults at the 2.5% MVC target force and lower at 30 and 65% MVC. For the 2.5% MVC target force, the decline in CV of force from vision to no vision was greater for elderly adults than for young adults. At 30 and 65% MVC, the decline was significant but similar for young and elderly adults. For elbow flexors, the change in power from vision to no vision was greater for 0- to 4-Hz (reduced power) and 8- to 12-Hz (increased power) frequencies for elderly adults compared with young adults. CONCLUSION: Visuomotor correction contributed to force fluctuations in large proximal muscles. The contribution was greater for healthy elderly adults at low forces. Visuomotor processes thus contributed to the age-related increase in force fluctuations.     

Effects of high‐intensity interval cycling performed after resistance training on muscle strength and hypertrophy

Aim of the study was to investigate whether high‐intensity interval cycling performed immediately after resistance training would inhibit muscle strength increase and hypertrophy expected from resistance training per se. Twenty‐two young men were assigned into either resistance training (RE; N = 11) or resistance training plus high‐intensity interval cycling (REC; N = 11). Lower body muscle strength and rate of force development (RFD), quadriceps cross‐sectional area (CSA) and vastus lateralis muscle architecture, muscle fiber type composition and capillarization, and estimated aerobic capacity were evaluated before and after 8 weeks of training (2 times per week). Muscle strength and quadriceps CSA were significantly and similarly increased after both interventions. Fiber CSA increased significantly and similarly after both RE (type I: 13.6 ± 3.7%, type IIA: 17.6 ± 4.4%, type IIX: 23.2 ± 5.7%, P < 0.05) and REC (type I: 10.0 ± 2.7%, type IIA: 14.8 ± 4.3% type IIX: 20.8 ± 6.0%, P < 0.05). In contrast, RFD decreased and fascicle angle increased (P < 0.05) only after REC. Capillary density and estimated aerobic capacity increased (P < 0.05) only after REC. These results suggest that high‐intensity interval cycling performed after heavy‐resistance exercise may not inhibit resistance exercise‐induced muscle strength/hypertrophy after 2 months of training, while it prompts aerobic capacity and muscle capillarization. The addition of high‐intensity cycling after heavy‐resistance exercise may decrease RFD partly due to muscle architectural changes.     

Strength training improves cycling performance,fractional utilization of VO2max and cycling economy in female cyclists

The purpose of this study was to investigate the effect of adding heavy strength training to well‐trained female cyclists’ normal endurance training on cycling performance. Nineteen female cyclists were randomly assigned to 11 weeks of either normal endurance training combined with heavy strength training (E+S, n = 11) or to normal endurance training only (E, n = 8). E+S increased one repetition maximum in one‐legged leg press and quadriceps muscle cross‐sectional area (CSA) more than E (P < 0.05), and improved mean power output in a 40‐min all‐out trial, fractional utilization of VO_2max and cycling economy (P < 0.05). The proportion of type IIAX‐IIX muscle fibers in m. vastus lateralis was reduced in E+S with a concomitant increase in type IIA fibers (P < 0.05). No changes occurred in E. The individual changes in performance during the 40‐min all‐out trial was correlated with both change in IIAX‐IIX fiber proportion (r = ?0.63) and change in muscle CSA (r = 0.73). In conclusion, adding heavy strength training improved cycling performance, increased fractional utilization of VO_2max, and improved cycling economy. The main mechanisms behind these improvements seemed to be increased quadriceps muscle CSA and fiber type shifts from type IIAX‐IIX toward type IIA.     

Sex differences in mechanomyographic responses to voluntary isometric contractions

PURPOSE: This study was designed to compare mechanomyography (MMG) and the force relationship during isometric ramp contractions of biceps brachii muscles in females and males to identify sex differences in the MMG responses. METHODS: Subjects (10 females and 9 males; age range, 20-26 yr) were asked to exert an isometric elbow flexion torque from 5 to 80% maximal voluntary contraction (MVC) at a constant rate of 10% MVC per second. The MMG signal was normalized to muscle cross-sectional area (CSA) as measured by ultrasound imaging. RESULTS: MVC and CSA were significantly different between the two sex groups (males>females); however, there was no sex difference in the MVC relative to muscle CSA (MVC/CSA). The root mean squared amplitude of the MMG (RMSMMG) was significantly greater in the male group than the female group. The RMSMMG relative to muscle CSA was also different between the two sex groups (males>females). The sex difference in the RMSMMG/CSA was more pronounced with increasing torque. The torque levels at which the inflection points in the MMG amplitude were located were different between the two sex groups. The mean power frequency (MPF) of the MMG in the female group increased monotonously, which was different from that in the male group. CONCLUSION: Our results suggest that the sex differences in MMG responses and motor unit (MU) activation strategy result from the predominant activity of the MU with slow-twitch fibers and an effective fused tetanus in females. In addition, the sex-related differences in muscle morphology, subcutaneous adipose tissue, and muscle stiffness appear to be insufficiently reflected in the present MMG responses, particularly relative to muscle CSA.     

Effect of swim taper on whole muscle and single muscle fiber contractile properties

TRAPPE, S., D. COSTILL, and R. THOMAS. Effect of swim taper on whole muscle and single muscle fiber contractile properties. Med. Sci. Sports Exerc., Vol. 32, No. 12, 2000, pp. 48-56. Purpose: To examine the changes in whole muscle function and single cell contractile properties of Type I and II muscle fibers from the deltoid muscle of highly trained swimmers before and after a 21-d reduction in training volume (taper). Methods: Six college male swimmers (age, 20 +/- 1 yr; height, 187 +/- 2 cm, weight, 79 +/- 3 kg, fat, 7 +/- 1%) who had been, on average, swimming 6200 m.d-1 for 5 months before the taper participated in this investigation. Results: Whole muscle power increased (P < 0.05) 17% and 13% on the swim bench and swim power tests, respectively. Swim times improved by 4% (range: 3.0-4.7%; P < 0.05). There was no change in Type I fiber diameter, whereas Type IIa fibers were 11% larger (P < 0.05) after taper. Peak force (Po) of the Type I fibers was unaffected by the taper but increased (P < 0.05) from 0.63 +/- 0.02 to 0.82 +/- 0.05 mN in the IIa fibers. However, the specific force (Po/CSA) of the IIa fibers was unchanged. Shortening velocity (Vo) was 32% and 67% faster (P < 0.05) in the Type I and IIa fibers, respectively. Although Type I fiber power was unaltered, the IIa fibers increased 2.5-fold from 24.6 +/- 2.8 to 56.2 +/- 3.9 μN.FL.s-1. When power was normalized for cell size, the power was still elevated twofold. Conclusions: These data suggest that tapering induces alterations in the contractile properties of single muscle fibers. Further, it appears that the Type IIa fibers are more affected than the Type I fibers by the taper. The increased size, strength, velocity, and power of the IIa fibers may be responsible for the improvements in whole muscle strength and power after the taper.     

Sex differences in single muscle fiber power in older adults

PURPOSE: This study was conducted to determine whether differences in power at the single muscle fiber level contribute to sex differences in whole muscle power production in the elderly. METHODS: A total of 16 sedentary older persons (10 women, 6 men), mean age 72 yr, had percutaneous needle biopsy of musculus vastus lateralis. Chemically skinned single muscle fibers were activated with Ca for maximal isometric force measurement (Po). The slack test was performed to determine maximal unloaded shortening velocity (Vo). Force-velocity and power curves were generated via a series of isotonic contractions, allowing measurement of peak power and specific power. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to determine myosin heavy chain composition of single muscle fibers. Whole muscle strength, velocity, and power were measured for knee extension and double leg press. RESULTS: Men had greater whole muscle strength, power, and velocity compared with women. Studied were 274 type I and 33 type IIa single fibers. No significant sex differences were found for fiber size, Po, specific force, Vo, power, or specific power in type I or IIa fibers. CONCLUSIONS: Single muscle fiber quality in older women is equivalent to that in older men and can not explain the differences seen in whole muscle strength, power, or function.     

Neuromuscular response of young boys versus men during sustained maximal contraction

PURPOSE: This study was designed to compare neuromuscular response between boys and men during sustained maximal voluntary contraction (MVC). METHODS: Fifteen boys (YB, 10.5 +/- 0.9 yr) and 12 men (AM, 21.5 +/- 4.5 yr) participated in the experiment. Arm's cross sectional area (CSA) and maximal force (F(max)) of elbow flexor were measured before subjects performed a 30-s sustained MVC. Mean power frequency (MPF) and muscle fiber conduction velocity (MFCV) were calculated from myoelectric signals of the biceps brachii. F(max)/CSA, MPF, and MFCV changes were expressed by slopes of linear regressions. Maximal MPF (I-MPF) and MFCV (I-MFCV) were derived from the intercept of each regression. RESULTS: AM had significantly greater F(max)/CSA (P < 0.05), I-MPF (P < 0.05), and I-MFCV (P < 0.01) than YB. F(max)/CSA (P < 0.001), MPF (P < 0.001), and MFCV (P < 0.01) declined significantly more for AM than YB. MPF/MFCV ratio increased, i.e., MPF decreased more than MFCV, for both groups but this was significantly (P < 0.001) more pronounced for AM. CONCLUSION: Taken together, those results suggest that more fatigable Type II motor units are involved in men, resulting in greater lactic acid and ions accumulations during fatigue. This difference in muscle's metabolic and ionic state could be responsible for a greater reflex-induced decrease of motor units firing rates in men compared with boys. This firing rate decrease could be explained using the "muscular wisdom" hypothesis and would express a nervous command adaptation to sustain a maximal contraction.     

Role of the nervous system in sarcopenia and muscle atrophy with aging: strength training as a countermeasure

Aging is characterized by loss of spinal motor neurons (MNs) due to apoptosis, reduced insulin-like growth factor I signaling, elevated amounts of circulating cytokines, and increased cell oxidative stress. The age-related loss of spinal MNs is paralleled by a reduction in muscle fiber number and size (sarcopenia), resulting in impaired mechanical muscle performance that in turn leads to a reduced functional capacity during everyday tasks. Concurrently, maximum muscle strength, power, and rate of force development are decreased with aging, even in highly trained master athletes. The impairment in muscle mechanical function is accompanied and partly caused by an age-related loss in neuromuscular function that comprise changes in maximal MN firing frequency, agonist muscle activation, antagonist muscle coactivation, force steadiness, and spinal inhibitory circuitry. Strength training appears to elicit effective countermeasures in elderly individuals even at a very old age (>80 years) by evoking muscle hypertrophy along with substantial changes in neuromuscular function, respectively. Notably, the training-induced changes in muscle mass and nervous system function leads to an improved functional capacity during activities of daily living.     

Evaluation of the strength-size relationship in vivo using various muscle size indices

PURPOSE: It is well accepted that maximum strength is related to muscle size. The primary purpose of this study was to determine whether anthropometric or dual-energy x-ray absorptiometry (DEXA) estimates of muscle size were valid predictors of plantar flexor maximum voluntary contraction (MVC) strength and could be used in lieu of more sophisticated techniques (e.g., magnetic resonance imaging (MRI)). Additionally, we compared the relationship among MVC and three MRI-determined muscle size measures; anatomical (ACSA) and physiological (PCSA) cross-sectional areas; and muscle volume (VOLm). METHODS: We measured plantar flexor MVC at 1.83 rad and various indices of muscle size: 1) body weight, 2) total body lean mass (LM) (DEXA), 3) lower leg LM (DEXA), 4) lower leg circumference, 5) estimated muscle+bone cross-sectional area (CSA) from circumference and calf skin-fold, 6) triceps surae ACSA, 7) triceps surae PCSA, and (8) triceps surae volume (VOLm), in 39 premenopausal women (mean +/- SD: 36 +/- 8 yr, 165 +/- 6 cm, and 65 +/- 9 kg). RESULTS: Zero-order correlations showed significant (P < 0.05) associations between MVC and total body LM (r = 0.365), lower leg LM (r = 0.381), circumference (r = 0.584), estimated muscle+bone CSA (r = 0.447), ACSA (r = 0.733), PCSA (r = 0.715), and VOLm (r = 0.649). By using the Fisher Z-transformation, ACSA and PCSA correlated significantly higher with MVC (P < 0.05) than anthropometric and DEXA indices. Further, only ACSA and PCSA regressed to the origin, indicating the ability to predict MVC was greatest with these two measures. CONCLUSIONS: The MRI-determined muscle size indices, which were specific to the triceps surae, correlated with strength better than whole limb anthropometric and DEXA indices. In this group of women, both ACSA and PCSA appeared superior to VOLm for predicting strength. PCSA was not found to be more precise than ACSA. ACSA appears to provide adequate precision for estimating plantar flexor specific tension in vivo.     

Effect of swim taper on whole muscle and single muscle fiber contractile properties

PURPOSE: To examine the changes in whole muscle function and single cell contractile properties of Type I and II muscle fibers from the deltoid muscle of highly trained swimmers before and after a 21-d reduction in training volume (taper). METHODS: Six college male swimmers (age, 20+/-1 yr; height, 187+/-2 cm, weight, 79+/-3 kg, fat, 7+/-1%) who had been, on average, swimming 6200 m x d(-1) for 5 months before the taper participated in this investigation. RESULTS: Whole muscle power increased (P < 0.05) 17% and 13% on the swim bench and swim power tests, respectively. Swim times improved by 4% (range: 3.0-4.7%; P < 0.05). There was no change in Type I fiber diameter, whereas Type IIa fibers were 11% larger (P < 0.05) after taper. Peak force (Po) of the Type I fibers was unaffected by the taper but increased (P < 0.05) from 0.63+/-0.02 to 0.82+/-0.05 mN in the IIa fibers. However, the specific force (Po/CSA) of the IIa fibers was unchanged. Shortening velocity (Vo) was 32% and 67% faster (P < 0.05) in the Type I and IIa fibers, respectively. Although Type I fiber power was unaltered, the IIa fibers increased 2.5-fold from 24.6+/-2.8 to 56.2+/-3.9 microN x FL x s(-1). When power was normalized for cell size, the power was still elevated twofold. CONCLUSIONS: These data suggest that tapering induces alterations in the contractile properties of single muscle fibers. Further, it appears that the Type IIa fibers are more affected than the Type I fibers by the taper. The increased size, strength, velocity, and power of the IIa fibers may be responsible for the improvements in whole muscle strength and power after the taper.     

Maximal strength and power, endurance performance, and serum hormones in middle-aged and elderly men

PURPOSE: To examine maximal strength, power and muscle cross-sectional area, maximal and submaximal cycling endurance characteristics, and serum hormone concentrations of testosterone (T), free testosterone (FT), and cortisol (C) in middle-aged and elderly men. METHODS: Maximal knee extension force (isometric; MIF(KE)), power-load curves during concentric actions with loads ranging from 15% to 70% of 1 RM half-squat (1RM(HS)), muscle cross-sectional area of quadriceps femoris (CSA(QF)), workload, heart rate and lactate accumulation during incremental cycling, and serum hormone concentrations were measured in 26 middle-aged (M42 yr) and 21 elderly men (M65 yr). RESULTS: The 1RM(HS) (14%), MIF(KE) (24%) and CSA(QF) (13%) were lower in M65 than in M42 (P < 0.05-0.01). Power during submaximal actions was lower (P < 0.05-0.001) in M65 than in M42, but the differences disappeared when expressed relative to CSA(QF). Serum FT was in M42 higher (P < 0.05) than in M65. Maximal workload, maximal heart rate and peak blood lactate during cycling in M65 were 31%, 11%, and 20% lower than in M42 (P < 0.01). During submaximal cycling blood lactate rose more rapidly with increasing workload in M65 than in M42 (P < 0.05-0.01), but the differences disappeared when expressed relative to CSA(QF). Significant correlations existed between individual values of serum FT:C ratio, C and T, and those of muscle strength and maximal workload. CONCLUSION: Declines in maximal strength, muscle mass, and endurance performance seem to take place with increasing age, although muscle power and demand for aerobic energy per unit of muscle tissue during submaximal loads remain similar. The balance between anabolic and catabolic hormones in aging people over the years may be associated with age-related decreased strength and declines in maximal cycling workload.     

Chronic exertional compartment syndrome: muscle changes with isometric exercise

Chronic exertional compartment syndrome (CECS) is a well-documented cause of lower leg pain in active individuals. The pathophysiology is unclear, although it is generally believed to be associated with increased intramuscular pressure, but there is very little information about muscle function in relation to the onset of pain. PURPOSE: To investigate strength, fatigue, and recovery of the anterior tibial muscles in CECS patients and healthy subjects during an isometric exercise protocol. METHODS: Twenty patients and 22 control subjects (mean age 27.6 yr and 33.0 yr, respectively) performed a 20-min isometric exercise protocol consisting of intermittent maximal voluntary contractions (MVC). Central fatigue was evaluated by comparing changes in electrically stimulated (2 s at 50 Hz) and voluntary contraction force before and during the exercise, and then throughout 10 min of recovery. Muscle size was measured by ultrasonography. Pain and cardiovascular parameters were also examined. RESULTS: The absolute MVC forces were similar, but MVC:body mass of the patients was lower (P < 0.05) as was the ratio of MVC to muscle cross-sectional area (P < 0.01). The extent of central and peripheral fatigue was similar in the two groups. The patients reported significantly higher levels of pain during exercise (P < 0.05 at 4 min) and after the first minute of recovery (P < 0.001). An 8% increase in muscle size after exercise was observed for both groups. There were no differences in the cardiovascular responses of the two groups. CONCLUSIONS: CECS patients were somewhat weaker than normal but fatigued at a similar rate during isometric exercise. Patients reported higher pain than controls despite comparable changes in muscle size, suggesting that abnormally tight fascia are not the main cause of CECS symptoms.