Early-Phase Satellite Cell and Myonuclear Domain Adaptations to Slow-Speed vs. Traditional Resistance Training Programs.

The purpose of this investigation was to identify adaptations in satellite cell (SC) content and myonuclear domain (MND) after 6-week slow-speed vs. "normal-speed" resistance training programs. Thirty-four untrained females were divided into slow speed (SS), traditional strength (TS), traditional muscular endurance (TE), and nontraining control (C) groups. Three sets each of leg press, squat, and knee extension were performed 2 days per week for the first week and 3 days per week for the following 5 weeks. The SS group performed 6-10 repetition maximum (6-10RM) for each set with 10-second concentric (con) and 4-second eccentric (ecc) contractions for each repetition. Traditional strength and TE performed 6-10RM and 20-30RM, respectively, at "normal" speed (1-2 seconds per con and ecc contractions). Traditional muscular endurance and SS trained at the same intensity (40-60% 1RM), whereas TS trained at 80-85% 1RM. Pretraining and posttraining muscle biopsies were analyzed for fiber cross-sectional area, fiber type, SC content, myonuclear number, and MND. Satellite cell content of type I, IIA, IIAX, and IIX fibers significantly increased in TS. However, SC content of only type IIAX and IIX fibers increased in SS, and there was no change in TE or C. Myonuclear number did not change in any group. Myonuclear domain of type I, IIA, IIAX, and IIX fibers increased in TS, whereas MND of only type IIA fibers increased in SS, and there was no change in TE or C. In conclusion, slow-speed resistance training increased SC content and MND more than training with a similar resistance at normal speed. However, high-intensity normal-speed training produced the greatest degree of fiber adaptation for each variable.

Effects of anabolic steroids and high-intensity aerobic exercise on skeletal muscle of transgenic mice.

In an attempt to shorten recovery time and improve performance, strength and endurance athletes occasionally turn to the illicit use of anabolic-androgenic steroids (AAS). This study evaluated the effects of AAS treatment on the muscle mass and phenotypic characteristics of transgenic mice subjected to a high-intensity, aerobic training program (5d/wk for 6 weeks). The transgenic mice (CETP(+/-)LDLr(-/+)) were engineered to exhibit a lipid profile closer to humans. Animals were divided into groups of sedentary (Sed) and/or training (Ex) mice (each treated orally with AAS or gum arabic/vehicle: Sed-C, Sed-M, ex-C, ex-M). The effects of AAS (mesterolone: M) on specific phenotypic adaptations (muscle wet weight, cross-sectional area, and fiber type composition) in three hindlimb muscles (soleus:SOL, tibialis anterior:TA and gastrocnemius:GAS) were assessed. In order to detect subtle changes in fiber type profile, the entire range of fiber types (I, IC, IIAC, IIA, IIAD, IID, IIDB, IIB) was delineated using mATPase histochemistry. Body weight gain occurred throughout the study for all groups. However, the body weight gain was significantly minimized with exercise. This effect was blunted with mesterolone treatment. Both AAS treatment (Sed-M) and high-intensity, aerobic training (ex-C) increased the wet weights of all three muscles and induced differential hypertrophy of pure and hybrid fibers. Combination of AAS and training (ex-M) resulted in enhanced hypertrophy. In the SOL, mesterolone treatment (Sed-M and ex-M) caused dramatic increases in the percentages of fiber types IC, IIAC, IIAD, IID, with concomitant decrease in IIA, but had minimal impact on fiber type percentages in the predominantly fast muscles. Overall, the AAS-induced differential adaptive changes amounted to significant fiber type transformations in the fast-to-slow direction in SOL. AAS treatment had a significant effect on muscle weights and fiber type composition in SOL, TA and GAS which was even maximized in animals subjected to metabolically high-intensity aerobic exercise.

Misclassification of hybrid fast fibers in resistance-trained human skeletal muscle using histochemical and immunohistochemical methods.

Sixteen healthy untrained women participated in a 6-week progressive resistance training program to compare 2 common methods of classifying fiber types. The women were a subset from a previous study and were randomly divided into 2 groups: traditional strength training (TS, n = 9) and non-exercising control (C, n = 7). The TS group performed 3 lower limb exercises (leg press, squat, and knee extension) using 6-10 repetitions maximum 2 days per week for the first week and 3 days per week for the remaining 5 weeks (17 total workouts). Pre- and posttraining vastus lateralis muscle biopsies were analyzed for fiber type composition using 2 popular methods: myosin adenosine triphosphatase (mATPase) histochemistry and myosin heavy chain (MHC) immunohistochemistry. Six fiber types (I, IC, IIC, IIA, IIAX, and IIX) were delineated using each method separately and in combination. Because of the subjective nature of each method (visual assessment of staining intensities), IIAX fibers expressing a small amount of MHCIIa were misclassified as type IIX using mATPase histochemistry, whereas those expressing a small amount of MHCIIx were misclassified as type IIA using MHC immunohistochemistry. As such, either method used separately resulted in an underestimation of the type IIAX fiber population. In addition, the use of mATPase histochemistry alone resulted in an overestimation of type IIX, whereas there was an overestimation of type IIA using MHC immunohistochemistry. These fiber typing errors were most evident after 6 weeks of resistance training when fibers were in transition from type IIX to IIA. These data suggest that the best approach to more accurately determine muscle fiber type composition (especially after training) is the combination of mATPase histochemical and MHC immunohistochemical methods.

Early-phase muscular adaptations in response to slow-speed versus traditional resistance-training regimens.

Thirty-four untrained women participated in a 6-week program to investigate slow-speed versus "normal" speed resistance-training protocols. Subjects were divided into: slow-speed (SS), normal-speed/traditional-strength (TS), normal-speed/traditional muscular endurance (TE), and non-exercising control (C) groups. Leg press, squats, and knee extensions were performed 2 days/week for the first week and 3 days/week for the remaining 5 weeks (~2 min rest). The SS group performed 6-10 repetitions maximum (6-10RM) for each set with 10 s concentric (con) and 4 s eccentric (ecc) contractions. The TS and TE groups performed sets of 6-10RM and 20-30RM, respectively, at "normal" speed (1-2 s/con and ecc contractions). TE and SS trained at the same relative intensity (~40-60% 1RM), whereas TS trained at ~80-85% 1RM. Pre- and post-training muscle biopsies were analyzed for fiber-type composition, cross-sectional area (CSA), and myosin heavy chain (MHC) content. The percentage of type IIX fibers decreased and IIAX increased in all three training groups. However, only TS showed an increase in percentage of type IIA fibers. CSA of fiber types I, IIA, and IIX increased in TS. In SS, only the CSA of IIA and IIX fibers increased. These changes were supported by MHC data. No significant changes for any parameters were found for the C group. In conclusion, slow-speed strength training induced a greater adaptive response compared to training with a similar resistance at "normal" speed. However, training with a higher intensity at "normal" speed resulted in the greatest overall muscle fiber response in each of the variables assessed.

Effects of 14 days of microgravity on fast hindlimb and diaphragm muscles of the rat.

The purpose of the present study was to determine the effects of 14 days of microgravity on specific rat fast-twitch muscles, and to compare these data with previous data from rat fast-twitch muscles exposed to microgravity for 10 days (Kraemer et al. 2000). Hindlimb muscles containing predominately fast fibers [extensor digitorum longus (EDL), superficial "white" (GSW) and deep "red" (GDR) gastrocnemius] and the diaphragm (DIA) were removed from flight and ground-based control animals and analyzed for: muscle mass, fiber type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content. Gravitational unloading for 14 days caused significant decreases in muscle mass (8-9%) and cross-sectional area of almost all fiber types (10-35%) from both EDL and gastrocnemius muscles. However, microgravity had little effect on fiber type composition in these muscles with significant changes occurring only in the EDL type IID fiber population (9.5% decrease). Similarly, relative MHC isoform content was only slightly altered by exposure to microgravity (increased content of MHCIIa in flight EDL). No changes in area, fiber type percentages, or MHC isoform content were detected in the DIA following the 14-day spaceflight. Similar to data gathered following a 10-day spaceflight (Kraemer et al. 2000), the 14-day flight did not appear to cause significant slow-to-fast (I --> IIA) or fast-to-faster (IIA --> IID --> IIB) transformations in hindlimb muscles containing predominantly fast-twitch fibers. However, the longer period of gravitational unloading did result in additional loss in muscle fiber cross-sectional area with involvement of more major fiber types.

Effect of circulating growth hormone on muscle IGF-I protein concentration in female mice with growth hormone receptor gene disruption.

Growth hormone (GH) is a potent secretague for circulating insulin-like growth factor-I (IGF-I). The purpose of this study was to examine the effect of circulating GH on muscle IGF-I protein expression using GH transgenic animal models. Three different models were used: mice that overexpress bovine GH (bGH; n=10), mice without a functional GH receptor (GHR-/-; n=10), and wildtype mice (n=10). All mice were 16-week old females and each group differed in their basic phenotypic characteristics. Immediately after euthanization the triceps surae muscle group (soleus, plantaris, and gastrocnemius muscles) was removed. IGF-I was extracted from the muscle with an acid-ethanol solution (12.5% 2N hydrochloric acid and 87.5% ethanol, pH 1.5) followed by neutralization with Tris-base and subsequently quantified using a radioimmunoassay. Analysis revealed that bGH mice had significantly greater muscle IGF-I protein expression compared to GHR-/- and wildtype mice. No difference in IGF-I protein concentration was found between GHR-/- and wildtype animals. This study found that overexpression of GH leading to high circulating GH concentrations increase muscle IGF-I protein expression. However, the absence of a functional GHR did not affect muscle IGF-I protein expression compared to wildtype despite high circulating levels of GH and low circulating levels of IGF-I. In conclusion, it appears that at rest high circulating levels of GH augment muscle IGF-I protein expression only in the presence of an intact GHR but that the absence of a functional GH receptor does not affect basal levels of muscle IGF-I protein in female mice.

Effects of growth hormone overexpression vs. growth hormone receptor gene disruption on mouse hindlimb muscle fiber type composition.

OBJECTIVE: The present study characterizes the fiber type composition of selected hindlimb muscles from two transgenic mouse lines specifically engineered to alter the amounts of circulating growth hormone (GH) and insulin-like growth factor-1 (IFG-1). DESIGN: The triceps surae muscle group (soleus m., gastrocnemius m., and plantaris m.) was harvested en masse from mice that were: (1) giant due to the expression of a bovine GH transgene (bGH), (2) dwarf due to the disruption of the GH receptor/binding protein gene (GHR-/-), and (3) normal-sized controls [non-transgenic (NT)]. Histochemical and immunohistochemical methods were utilized on serial cross sections to delineate eight fiber types (I, IC, IIC, IIA, IIAD, IID, IIDB, and IIB). Cross-sectional areas were subsequently determined on approximately 50 fibers/type. RESULTS: Compared to NT littermates, muscles from bGH mice demonstrated a significant (p<0.05) fast-to-slow shift in fiber phenotype, as well as significantly larger fibers for most types. In contrast, significantly smaller fibers were found for all fiber types in the GHR-/- mice, with no significant differences in fiber type percentages compared to NT. Regardless of mouse genotype, the hierarchy of fiber size was maintained in each muscle with type I the largest in the soleus m. and type IIB the largest in the predominantly fast muscles (plantaris, superficial and deep gastrocnemius muscles). CONCLUSION: In conclusion, the genetic manipulation of GH expression (bGH) and its receptor binding (GHR-/-) had profound and divergent effects on muscle phenotype. It is hoped that continued research in this area will help elucidate the direct (independent of IGF-1) vs. indirect (via IGF-1 mediating mechanisms) effects of GH.

Comparison of early phase adaptations for traditional strength and endurance, and low velocity resistance training programs in college-aged women.

The purpose of this study was to investigate the effects of a six-week (16-17 training sessions) low velocity resistance training program (LV) on various performance measures as compared to a traditional strength (TS) and a traditional muscular endurance (TE) resistance training program. Thirty-four healthy adult females (21.1 +/- 2.7 y) were randomly divided into 4 groups: control (C), TS, TE, and LV. Workouts consisted of 3 exercises: leg press (LP), back squat (SQ), and knee extension (KE). Each subject was pre- and posttested for 1 repetition maximum (1RM), muscular endurance, maximal oxygen consumption (VO2max), muscular power, and body composition. After the pretesting, TS, TE, and LV groups attended a minimum of 16 out of 17 training sessions in which the LP, SQ, and KE were performed to fatigue for each of 3 sets. For each training session, TS trained at 6-10 RM and TE trained at 20-30 RM both with 1-2 second concentric/1-2 second eccentric; and LV trained at 6-10 RM, with 10 second concentric/4 s eccentric. Statistical significance was determined at an alpha level of 0.05. LV increased relative LP and KE 1 RM, but the percent increase was smaller than TS, and not different from C in the SQ. For muscular endurance, LV improved similarly to TE for LP and less than TS and TE for KE. Body composition improved for all groups including C (significant main effect). In conclusion, muscular strength improved with LV training however, TS showed a larger improvement. Muscular endurance improved with LV training, but not above what TE or TS demonstrated. For all other variables, there were no significant improvements for LV beyond what C demonstrated.

Effects of growth hormone and insulin-like growth factor I on muscle in mouse models of human growth disorders.

The precise effects of growth hormone (GH) and insulin-like growth factor I (IGF-I) on muscle development and physiology are relatively unknown. Furthermore, there have been conflicting reports on the effects of GH/IGF-I on muscle. Distinguishing the direct effects of GH versus those of IGF-I is problematic, but animal models with altered GH/IGF-I action could help to alleviate some of the conflicting results and help to determine the independent actions of GH and IGF-I. The phenotypes of several mouse models, namely the GH receptor-gene-disrupted (GHR -/-) mouse and a variety of IGF-I -/- mice, are summarized, which ultimately will aid our understanding of this complex area.

Fasted-state skeletal muscle protein synthesis after resistance exercise is altered with training.

The purpose of the present investigation was to determine how fasted-state protein synthesis was affected, acutely, by resistance training. Eight men (24.8+/-1.7 years, body mass index=23.2+/-1.0 kg m-2; means+/-s.e.m.) undertook an 8 week programme of unilateral resistance exercise training (3 sessions week-1, progression from two to four sets; intensity was 80% of the subjects' single repetition maximum (1RM): knee extension and leg press). Following training, subjects underwent two primed constant infusions of l-[ring-13C6]phenylalanine to determine mixed and myofibrillar muscle protein synthesis (MPS) at rest and 12 h after an acute bout of resistance exercise at the same exercise intensity--each leg 80% of 1RM. Biopsies (vastus lateralis) were taken to measure incorporation of labelled phenylalanine into mixed and myofibrillar skeletal muscle proteins and yield fractional MPS. Training resulted in significant dynamic strength gains that were greater (P<0.001) in the trained leg. Hypertrophy of type IIa and IIx fibres (P<0.05) was observed following training. After training, resting mixed MPS rate was elevated (+48%; P<0.05). Acutely, resistance exercise stimulated mixed MPS only in the untrained leg (P<0.05). Myofibrillar MPS was unchanged at rest following training (P=0.61). Myofibrillar MPS increased after resistance exercise (P<0.05), but was not different between the trained and untrained legs (P=0.36). We observed divergent changes in resting mixed versus myofibrillar protein synthesis with training. In addition, resistance training modified the acute response of MPS to resistance exercise by dampening the increased synthesis of non-myofibrillar proteins while maintaining the synthesis of myofibrillar proteins.

Short-term high- vs. low-velocity isokinetic lengthening training results in greater hypertrophy of the elbow flexors in young men.

We performed two studies to determine the effect of a resistive training program comprised of fast vs. slow isokinetic lengthening contractions on muscle fiber hypertrophy. In study I, we investigated the effect of fast (3.66 rad/s; Fast) or slow (0.35 rad/s; Slow) isokinetic high-resistance muscle lengthening contractions on muscle fiber and whole muscle cross-sectional area (CSA) of the elbow flexors was investigated in young men. Twelve subjects (23.8 +/- 2.4 yr; means +/- SD) performed maximal resistive lengthening isokinetic exercise with both arms for 8 wk (3 days/wk), during which they trained one arm at a Fast velocity while the contralateral arm performed an equivalent number of contractions at a Slow velocity. Before (Pre) and after (Post) the training, percutaneous muscle biopsies were taken from the midbelly of the biceps brachii and analyzed for fiber type and CSA. Type I muscle fiber size increased Pre to Post (P < 0.05) in both Fast and Slow arms. Type IIa and IIx muscle fiber CSA increased in both arms, but the increases were greater in the Fast- vs. the Slow-trained arm (P < 0.05). Elbow flexor CSA increased in Fast and Slow arms, with the increase in the Fast arm showing a trend toward being greater (P = 0.06). Maximum torque-generating capacity also increased to a greater degree (P < 0.05) in the Fast arm, regardless of testing velocity. In study II, we attempted to provide some explanation of the greater hypertrophy observed in study I by examining an indicator of protein remodeling (Z-line streaming), which we hypothesized would be greater in the Fast condition. Nine men (21.7 +/- 2.4 yr) performed an acute bout (n = 30, 3 sets x 10 repetitions/set) of maximal lengthening contractions at Fast and Slow velocities used in the training study. Biopsies revealed that Fast lengthening contractions resulted in more (185 +/- 1 7%; P < 0.01) Z-band streaming per millimeter squared muscle vs. the Slow arm. In conclusion, training using Fast (3.66 rad/s) lengthening contractions leads to greater hypertrophy and strength gains than Slow (0.35 rad/s) lengthening contractions. The greater hypertrophy seen in the Fast-trained arm (study I) may be related to a greater amount of protein remodeling (Z-band streaming; study II).

Treadmill training-induced adaptations in muscle phenotype in persons with incomplete spinal cord injury.

Body weight-supported treadmill (BWST) training has been shown to improve ambulatory capacity in persons with a spinal cord injury (SCI); however, the effect that BWST training has on skeletal muscle phenotype is unknown. We aimed to determine whether 6 months (three sessions/week) of BWST training in neurologically stable persons with a traumatic spinal cord injury (ASIA C) alters skeletal muscle phenotype, ambulatory capacity, and blood lipid profile. Externally supported body weight decreased, and walking velocity and duration of the training sessions increased (all P < 0.05) as a result of training. Muscle biopsies revealed increases in the mean muscle-fiber area of type I and IIa fibers. Training induced a reduction in type IIax/IIx fibers, as well as a decrease in IIX myosin heavy chain, and an increase in type IIa fibers. Maximal citrate synthase and 3-hydroxy-acyl-CoA dehydrogenase activity also increased following training. BWST training brought about reductions in plasma total (-11%) and low-density lipoprotein (-13%) cholesterol. We conclude that, in patients with a spinal cord injury, BWST training is able to induce an increase in muscle fiber size and bring about increases in muscle oxidative capacity. In addition, BWST training can bring about improvements in ambulatory capacity and antiatherogenic changes in blood lipid profile.

Responses of plasma proenkephalin peptide F in rats following 14 days of spaceflight.

INTRODUCTION: . Proenkephalin peptide F [107-140] is related to the enhancement of immune function, while microgravity has been shown to cause immuno-suppression. We investigated the physiological response of proenkephalin peptide F to microgravity. METHODS: There were 12 Fischer 344 female rats, ovariectomized at 10.5 wk of age, used to determine plasma concentrations of peptide F in response to a 14-d flight aboard the Columbia Space Shuttle mission STS-62. There were 36 other such rats that served as ground-based controls to separate the effects of microgravity from those of thermal stress, flight stress, and crowded habitats. Control groups of 12 rats each were kept under the following conditions: 1) 22 degrees C vivarium, 2) 28 degrees C vivarium, and 3) variable (Var) to mimic flight. The flight and control groups were housed in animal enclosure modules 21 d prior to flight and for the duration of the study. The rats were sacrificed within 4-5 h after landing, at which time blood samples were obtained. RESULTS: Body weights were obtained prior to sacrifice; mean values were flight, 199 g; 22 degrees C, 193 g; 28 degrees C, 192 g; and Var, 194 g. The flight group produced a significantly greater (p < or = 0.05) level of plasma peptide F (0.056 pmol x ml(-1)) compared with the controls (0.016, 0.022, and 0.016 pmol x ml(-1) for 22 degrees C, 28 degrees C, and Var, respectively). Flight animals demonstrated higher corticosterone concentrations and reduced T and B cell splenocyte counts than controls. CONCLUSIONS: These data indicate that the increases in proenkephalin peptide F observed with exposure to microgravity may present an adrenal-medullary response to cope with the decreased immune function and increased stress experienced during spaceflight and landing.

Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters.

Biopsies fro the vastus lateralis muscle of male weightlifters (WL; n=6; X +/- SE, age=27.0 +/- 2.1 years), and non-weight-trained men (CON; n=7; age=27.0 +/- 2.0 years) were compared for fiber types, myosin heavy chain (MHC) and titin content, and fiber type-specific capillary density. Differences (p<0.05) were observed for percent fiber types IIC (WL=0.4 +/- 0.2, CON=2.4 +/- 0.8); IIA (WL=50.5 +/- 3.2, CON=26.9 +/- 3.7); and IIB (WL=1.7 +/- 1.4, CON=21.0 +/- 5.3), as well as percent MHC IIa (WL=65.3 +/- 2.4, CON=52.1 +/- 4.2) and percent MHC IIB (WL=0.9 +/- 0.9; CON=18.2 +/- 6.1). All WL exhibited only the titin-1 isoform. Capillary density (caps.mm(-2)) for all fiber types combined was greater for the CON subjects (WL=192.7 +/- 17.3; CON=262.9 +/- 26.3), due primarily to a greater capillary density in the IIA fibers. Weightlifting performances and vertical jump power were correlated with type II fiber characteristics. These results suggest that successful weightlifting performance is not dependent on IIB fibers, and that weightlifters exhibit large percentages of type IIA muscle fibers and MHC IIa isoform content.

Postmortem alterations in the pH range of myofibrillar ATPase activation/inactivation.

A histochemical assay for myofibrillar adenosine triphosphatase (mATPase) activity is routinely utilized in the delineation of fiber types in healthy human skeletal muscle. Each fiber type has a specific pH range of mATPase stability (activation). Outside of this pH range, mATPase activity is labile (inactivated), no reaction product is formed, and the fibers remain unstained. The aim of the present study was to carefully investigate the pH stability/lability of mATPase in postmortem muscles. To this end, vastus lateralis muscle samples were obtained approximately 0.5, 1, 2, 3, and 4 days after death, as well as control samples from a healthy young man and woman. Serial cross sections of the muscle samples were assayed for mATPase activity throughout preincubation pH ranges of 4.15-4.7 and 10.2-10.5 in increments of 0.05 pH units. Myosin heavy chain analysis (as well as a regression analysis comparing fiber type area and relative myosin heavy chain content) verified the mATPase-based fiber types. The pH ranges of mATPase stability/lability for the control samples were as previously reported, and support the use of preincubation pH values of 4.3, 4.6, and 10.4 for the delineation of fiber types in normal human muscle. For the postmortem samples, both quantitative and qualitative changes altered the pH ranges of mATPase activation/inactivation. Quantitative changes consisted of a time-dependent loss of mATPase activity that was inhibited in all fibers outside the pH range of 4.15-10.50. In addition, qualitative changes caused "shifts to the left" in mATPase stability within the fast fiber types (IIA and IIB). As such, complete inhibition of mATPase activity did not occur until preincubation at pH 4.45 and pH 4.30 for fiber types IIA and IIB, respectively. For the postmortem vastus lateralis muscle samples, optimal preincubation pH values for mATPase-based fiber type delineation were pH 4.30, 4.45, and 10.35. The reason for these qualitative changes in mATPase stability is not known. However, postmortem changes such as increased lactate production and marked acidification may play a role.

Statistical analysis of fiber area in human skeletal muscle.

Previous research has indicated that 50 fiber measurements per individual for type I and II fibers would be sufficient to characterize the fiber areas. This study replicated the work of McCall et al. (1998) using the three major fiber types (I, IIA, and IIB) and sampling larger populations of fibers. Random blocks of fibers were also examined to investigate how well they correlated with the overall mean average fiber area. Using random blocks of 50 fibers provided an accurate reflection of the type IIB fibers (r = 0.96-0.98) but not for the type I (r = 0.85-0.94) or IIA fibers (r = 0.80-0.91). Type I fibers were consistently reflected by a random block of 150 fibers (r = 0.95-0.98) while type IIA fibers required random blocks of 200 fibers (r = 0.94-0.98), which appeared to provide an accurate reflection of the cross-sectional area. These results indicate that for a needle biopsy different numbers of fibers are needed depending on the fiber type to accurately characterize the mean fiber population.

Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones.

Thirty-two untrained men [mean (SD) age 22.5 (5.8) years, height 178.3 (7.2) cm, body mass 77.8 (11.9) kg] participated in an 8-week progressive resistance-training program to investigate the "strength-endurance continuum". Subjects were divided into four groups: a low repetition group (Low Rep, n = 9) performing 3-5 repetitions maximum (RM) for four sets of each exercise with 3 min rest between sets and exercises, an intermediate repetition group (Int Rep, n = 11) performing 9-11 RM for three sets with 2 min rest, a high repetition group (High Rep, n = 7) performing 20-28 RM for two sets with 1 min rest, and a non-exercising control group (Con, n = 5). Three exercises (leg press, squat, and knee extension) were performed 2 days/week for the first 4 weeks and 3 days/week for the final 4 weeks. Maximal strength [one repetition maximum, 1RM), local muscular endurance (maximal number of repetitions performed with 60% of 1RM), and various cardiorespiratory parameters (e.g., maximum oxygen consumption, pulmonary ventilation, maximal aerobic power, time to exhaustion) were assessed at the beginning and end of the study. In addition, pre- and post-training muscle biopsy samples were analyzed for fiber-type composition, cross-sectional area, myosin heavy chain (MHC) content, and capillarization. Maximal strength improved significantly more for the Low Rep group compared to the other training groups, and the maximal number of repetitions at 60% 1RM improved the most for the High Rep group. In addition, maximal aerobic power and time to exhaustion significantly increased at the end of the study for only the High Rep group. All three major fiber types (types I, IIA, and IIB) hypertrophied for the Low Rep and Int Rep groups, whereas no significant increases were demonstrated for either the High Rep or Con groups. However, the percentage of type IIB fibers decreased, with a concomitant increase in IIAB fibers for all three resistance-trained groups. These fiber-type conversions were supported by a significant decrease in MHCIIb accompanied by a significant increase in MHCIIa. No significant changes in fiber-type composition were found in the control samples. Although all three training regimens resulted in similar fiber-type transformations (IIB to IIA), the low to intermediate repetition resistance-training programs induced a greater hypertrophic effect compared to the high repetition regimen. The High Rep group, however, appeared better adapted for submaximal, prolonged contractions, with significant increases after training in aerobic power and time to exhaustion. Thus, low and intermediate RM training appears to induce similar muscular adaptations, at least after short-term training in previously untrained subjects. Overall, however, these data demonstrate that both physical performance and the associated physiological adaptations are linked to the intensity and number of repetitions performed, and thus lend support to the "strength-endurance continuum".

Human muscle power output during upper- and lower-body exercises.

The purpose of this study was to evaluate the use of traditional resistance training equipment in the measurement of muscular power. This was accomplished by measuring the velocity of movement through a measured distance during maximal effort lifts using a Smith rack. The reliability of the method was established using 10 male volunteers who performed both bench press and squat exercises in a Smith rack. Maximal power output was determined at 30, 40, 50, 60, 70, 80, and 90% of the subject's 1 repetition maximum (1RM). Test-retest power values were not statistically different. Another 15 male volunteers who had previous muscle biopsy data from the vastus lateralis muscle performed the same maximal power output evaluation. There were no significant relationships between peak power outputs and fiber-type expressions when linear regressions were performed. The power curve produced by graphing power output vs. the percentage of 1RM indicates that peak power output occurs between 50 and 70% of 1RM for the squat and between 40 and 60% of 1RM for the bench press. These data indicate that this method of evaluation of muscle power is reliable, although it is not predictive of muscle fiber-type percentages.

Creatine supplementation improves muscular performance in older men.

PURPOSE: Creatine supplementation has been shown to enhance muscle strength and power after only 5-7 d in young adults. Creatine supplementation could therefore benefit older individuals because aging is associated with a decrease in muscle strength and explosive power. METHODS: We examined the effects of 7 d of creatine supplementation in normally active older men (59-72 yr) by using a double-blind, placebo-controlled design with repeated measures. After a 3-wk familiarization period to minimize learning effects, a battery of tests was completed on three occasions separated by 7 d (T1, T2, and T3). After T1, subjects were matched and randomly assigned into creatine (N = 10) and placebo (N = 8) groups. After T2, subjects consumed supplements (0.3 g x kg(-1) x d(-1)) for 7 d until T3. All subjects were tested for maximal dynamic strength (one-repetition maximum leg press and bench press), maximal isometric strength (knee extension/flexion), upper- and lower-body explosive power (6 x 10-s sprints on a cycle ergometer), and lower-extremity functional ability (timed sit-stand test and tandem gait test). Body composition was assessed via hydrostatic weighing, and blood samples were obtained to assess renal and hepatic responses and muscle creatine concentrations. RESULTS: No significant increases in any performance measures were observed from T1 to T2 with the exception of isometric right-knee flexion in the placebo group indicating stability in the testing protocols. Significant group-by -time interactions indicated the responses from T2 to T3 were significantly greater (P