Relation between in vivo and in vitro measurements of skeletal muscle oxidative metabolism.

The relationships between in vivo (31)P magnetic resonance spectroscopy (MRS) and in vitro markers of oxidative capacity (mitochondrial function) were determined in 27 women with varying levels of physical fitness. Following 90-s isometric plantar flexion exercises, calf muscle mitochondrial function was determined from the phosphocreatine (PCr) recovery time constant, the adenosine diphosphate (ADP) recovery time constant, the rate of change of PCr during the initial 14 s of recovery, and the apparent maximum rate of oxidative adenosine triphosphate (ATP) synthesis (Q(max)). Muscle fiber type distribution (I, IIa, IIx), citrate synthase (CS) activity, and cytochrome c oxidase (COX) activity were determined from a biopsy sample of lateral gastrocnemius. MRS markers of mitochondrial function correlated moderately (P < 0.05) with the percentage of type IIa oxidative fibers (r = 0.41 to 0.66) and CS activity (r = 0.48 to 0.64), but only weakly with COX activity (r = 0.03 to 0.26, P > 0.05). These results support the use of MRS to determine mitochondrial function in vivo.

The interrelationship among muscle mass, strength, and the ability to perform physical tasks of daily living in younger and older women.

The purpose of this study was to objectively compare the difficulty and determine the contribution of strength and muscle mass to the performance of physical tasks of daily living in a group of younger and older women. A cross-sectional design was used. Volunteer participants were from the community of Birmingham, AL; there were 21 older (aged 60-75 years) and 20 younger (23-34 years) healthy women in the study. Subjects were matched for height and weight. Their testing included total and regional body composition evaluation by use of dual-energy x-ray absorptiometry, isometric strength tests of elbow flexors and knee extensors, and integrated electromyography (IEMG) evaluation while the subjects were standing from and sitting into a chair, and while they were carrying a small load (weight relative to strength). A two-way analysis of variance and a two-way analysis of covariance with repeated measures, Pearson product correlation, and first-order partial correlations were used to analyze the data. A significant inverse correlation was observed between age and isometric strength of both the knee extensors and elbow flexors. Adjusting for upper leg lean tissue did not change the significant inverse correlation between age and knee extensor strength. However, after an adjustment for arm lean tissue, there was no significant correlation between elbow flexor strength and age. Older women experienced significantly greater difficulty in standing than younger women as measured by quadriceps normalized IEMG (i.e., IEMG during task/IEMG during maximum isometric strength test). This difference persisted even after the covariate upper leg lean tissue was added to the model. No significant difference was observed between younger and older women for difficulty (biceps normalized IEMG) during the carry task after the covariate arm lean tissue was added to the model. The older women in this study had less strength in the knee extensors and experienced greater difficulty standing from a chair than the younger women, even after the covariate upper leg lean tissue was added to the model. This suggests that other factors, in addition to loss of lean tissue, contribute to the age-related decline of muscular strength and the ability to perform tasks with the legs. In contrast, although elbow flexor strength declined, this appeared to be largely due to decreased arm lean tissue mass.

High-resistance versus variable-resistance training in older adults.

PURPOSE: The purpose of this study was to compare the effects of high-resistance (HR) training, 3 times.wk(-1) at 80% maximum strength (1RM) with 3 times.wk(-1) variable-resistance (VR) training (once-weekly training at 80%, 65%, and 50% 1RM) in older adults. METHODS: The study was a 6-month resistance training intervention conducted in the Birmingham Alabama metropolitan area, and included healthy volunteer men and women over the age of 60. Twenty-eight subjects were assigned randomly to two training groups. Eight volunteers served as controls. Before and after 25 wk of training, body composition was measured by densitometry; strength by isometric tests; and difficulty in performing daily activity tasks (DAT) by measuring heart rate, oxygen uptake, electromyography, and perceived exertion. In addition, 1RM strength was measured every 25 d throughout the 6 months of training. Repeated measures ANOVA and paired t-tests with Bonferroni corrections for additive alpha were used to analyze the data. RESULTS: The control group did not significantly change in any study parameter. No significant change in body weight occurred for any group. However, the HR and VR groups increased fat free mass (FFM) similarly (1.8 kg and 1.9 kg, respectively). Both training groups increased strength significantly, without significant differences in change. No significant change in oxygen uptake occurred during DAT. However, there was a significant time effect for heart rate and perceived exertion. Greater decrease in normalized integrated electromyography during the carry task was found in the VR group over the HR and control groups. CONCLUSION: Despite similar increases in strength and fat free mass, the VR group decreased difficulty of performing the carry task more than the HR group. These data suggest that larger improvements in DAT may be achieved if frequency of high-resistance training is less than 3 times.wk(-1).

Muscle metabolic economy is inversely related to exercise intensity and type II myofiber distribution.

It is not known what causes the well-established inverse relationship between whole-body exercise economy and exercise intensity. The purpose of this study was to: (1) evaluate muscle exercise economy at 45%, 70%, and maximum isometric strength using 31P magnetic resonance spectroscopy (31P-MRS); and (2) determine the relationship between percent type II muscle fiber cross-section, whole-body exercise economy, and muscle exercise economy. Subjects included 32 premenopausal women. Muscle exercise economy was significantly different across the three exercise intensities (28.1 +/- 10.4, 24.8 +/- 8.2, and 20.2 +/- 7.5 N/cm2. mmol/L adenosine triphosphate [ATP] for the 45%, 70%, and maximum intensities, respectively). Percent type II muscle area was significantly related to whole-body metabolic economy during activities of daily living (r = -0.68) and 31P-MRS muscle metabolic economy during isometric plantar flexion (r = -0.53). These data suggest that skeletal muscle becomes less economical as force production increases, and that these decreases in metabolic economy may be related to increased dependence on inefficient type II muscle.

Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans.

The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 +/- 0.7 yr, 174.5 +/- 2.6 cm, 70.9 +/- 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6-10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC (P < 0.05). Changes after CON were similar but not significant (P = 0.06-0.12). AR mRNA concentration increased (P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC (P < 0.05). Perceived soreness was higher (P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.

Resistance training increases total energy expenditure and free-living physical activity in older adults.

The purpose of this study was to determine what effects 26 wk of resistance training have on resting energy expenditure (REE), total free-living energy expenditure (TEE), activity-related energy expenditure (AEE), engagement in free-living physical activity as measured by the activity-related time equivalent (ARTE) index, and respiratory exchange ratio (RER) in 61- to 77-yr-old men (n = 8) and women (n = 7). Before and after training, body composition (four-compartment model), strength, REE, TEE (doubly labeled water), AEE (TEE - REE + thermic response to meals), and ARTE (AEE adjusted for energy cost of standard activities) were evaluated. Strength (36%) and fat-free mass (2 kg) significantly increased, but body weight did not change. REE increased 6.8%, whereas resting RER decreased from 0.86 to 0.83. TEE (12%) and ARTE (38%) increased significantly, and AEE (30%) approached significance (P = 0.06). The TEE increase remained significant even after adjustment for the energy expenditure of the resistance training. In response to resistance training, TEE increased and RER decreased. The increase in TEE occurred as a result of increases in both REE and physical activity. These results suggest that resistance training may have value in increasing energy expenditure and lipid oxidation rates in older adults, thereby improving their metabolic profiles.

In situ localization of cholesterol in skeletal muscle by use of a monoclonal antibody.

A common perception is that cholesterol, the major structural lipid found in mammalian membranes, is localized nearly exclusively to the plasma membrane of living cells and that it is found in much smaller quantities in internal membranes. This perception is based almost exclusively on cell fractionation studies, in which density gradient centrifugation is used for purification of discrete subcellular membrane fractions. Here we describe a monoclonal antibody, MAb 2C5-6, previously reported to detect purified cholesterol in synthetic membranes (Swartz GM Jr, Gentry MK, Amende LM, Blanchette-Mackie EJ, and Alving CR. Proc Natl Acad Sci USA 85: 1902-1906, 1988), that is capable of detecting cholesterol in situ in the membranes of skeletal muscle sections. Localization of cholesterol, the dihydropyridine receptor of the T tubule, and the Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA2) by means of double and triple immunostaining protocols clearly demonstrates that cholesterol is primarily localized to the sarcoplasmic reticulum membranes of skeletal muscle rather than the sarcolemmal or T tubule membranes. The availability of this reagent and its ability to spatially localize cholesterol in situ may provide a greater understanding of the relationship between membrane cholesterol content and transmembrane signaling in skeletal muscle.

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.

Resistance exercise countermeasures for space flight: implications of training specificity.

While resistance exercise should be a logical choice for prevention of strength loss during unloading, the principle of training specificity cannot be overlooked. Our purpose was to explore training specificity in describing the effect of our constant load exercise countermeasure on isokinetic strength performance. Twelve healthy men (mean +/- SD: 28.0 +/- 5.2 years, 179.4 +/- 3.9 cm, 77.5 +/- 13.6 kg) were randomly assigned to no exercise or resistance exercise (REX) during 14 days of bed rest. REX performed five sets of leg press exercise to volitional fatigue (6-10 repetitions) every other day. Unilateral isokinetic concentric-eccentric knee extension testing performed before and on day 15 prior to reambulation included torque-velocity and power-velocity relationships at four velocities (0.52, 1.75, 2.97, and 4.19 rad s-1), torque-position relationship, and contractile work capacity (10 repetitions at 1.05 rad s-1). Two (group) x 2 (time) ANOVA revealed no group x time interactions; thus, groups were combined. Across velocities, angle-specific torque fell 18% and average power fell 20% (p < 0.05). No velocity x time or mode (concentric/eccentric) x time interactions were noted. Torque x position decreased on average 24% (p < 0.05). Total contractile work dropped 27% (p < 0.05). Results indicate bed rest induces rapid and marked reductions in strength and our constant load resistance training protocol did not prevent isokinetic strength losses. Differences between closed-chain training and open-chain testing may explain the lack of protection.

Enhanced protein electrophoresis technique for separating human skeletal muscle myosin heavy chain isoforms.

Talmadge and Roy (J. Appl. Physiol. 1993, 75, 2337-2340) previously established a sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) protocol for separating all four rat skeletal muscle myosin heavy chain (MHC) isoforms (MHC I, IIa, IIx, IIb); however, when applied to human muscle, the type II MHC isoforms (Ila, IIx) are not clearly distinguished. In this brief paper we describe a modification of the SDS-PAGE protocol which yields distinct and consistent separation of all three adult human MHC isoforms (MHC I, IIa, IIx) in a minigel system. MHC specificity of each band was confirmed by Western blot using three monoclonal IgG antibodies (mAbs) immunoreactive against MHCI (mAb MHCs, Novacastra Laboratories), MHCI+IIa (mAb BF-35), and MHCIIa+IIx (mAb SC-71). Results provide a valuable SDS-PAGE minigel technique for separating MHC isoforms in human muscle without the difficult task of casting gradient gels.

Bed rest decreases mechanically induced myofiber wounding and consequent wound-mediated FGF release.

Using a terrestrial model of spaceflight (i.e., bed rest), we investigated the amount of myofiber wounding and fibroblast growth factor (FGF) release that occurs during unloading. Myofiber wounding was determined by serum levels of the creatine kinase MM (CKMM) isoform before and after bed rest. Serum levels of both acidic FGF (aFGF) and basic FGF were also determined. A second group of subjects was treated in an identical fashion except that they underwent a resistive exercise program during bed rest. Bed rest alone caused significant (P < 0.05; n = 7) reductions in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by a significant (P < 0.05; n = 7) decrease in myofiber size. In contrast, bed rest plus resistive exercise resulted in significant (P < 0.05; n = 7) increases in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by inhibition of the atrophic response. These results suggest that mechanically induced, myofiber wound-mediated FGF release may play an important role in the etiology of unloading-induced skeletal muscle atrophy.

A role for high intensity exercise on energy balance and weight control.

The objective of this commentary is to remark on the impact, exercise intensity has on energy expenditure and its potential for body weight control. Exercise intensity can favorably impact on energy expenditure in a number of ways. First, exercise-associated energy expenditure is increased by decreasing exercise efficiency and increasing work rate. Second, resistance training that increases muscle mass, in turn increases resting energy expenditure. Third, aerobic exercise > 70% VO2max, increases resting energy expenditure separate from any change in muscle mass. High-intensity exercise training has the added benefit of improving fitness, thus making low-intensity exercise less difficult and more easily tolerated. Although continuous intense exercise is difficult to maintain for extended periods of time, intense interval exercise can be easily endured and may be an important adjunct to lifestyle modifications for body weight control.

Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution.

Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx (n = 8). REx performed five sets of leg press exercise with 80-85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions (P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased (P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced (P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.

Resistance exercise prevents plantar flexor deconditioning during bed rest.

Because resistance exercise (REX) and unloading induce opposing neuromuscular adaptations, we tested the efficacy of REX against the effects of 14 d of bed rest unloading (BRU) on the plantar flexor muscle group. Sixteen men were randomly assigned to no exercise (NOE, N = 8) or REX (N = 8). REX performed 5 sets x 6-10 repetitions to failure of constant resistance concentric/eccentric plantar flexion every other day during BRU. One-repetition maximum (1RM) strength was tested on the training device. The angle-specific torque-velocity relationship across 5 velocities (0, 0.52, 1.05, 1.75, and 2.97 rad.s-1) and the full range-of-motion power-velocity relationship were assessed on a dynamometer. Torque-position analyses identified strength changes at shortened, neutral, and stretched muscle lengths. Concentric and eccentric contractile work were measured across ten repetitions at 1.05 rad.s-1. Maximal neural activation was measured by surface electromyography (EMG). 1RM decreased 9% in NOE and improved 11% in REX (P < 0.05). Concentric (0.52 and 1.05 rad.s-1), eccentric (0.52 and 2.97 rad.s-1), and isometric angle-specific torques decreased (P < 0.05) in NOE, averaging 18%, 17%, and 13%, respectively. Power dropped (P < 0.05) in NOE at three eccentric (21%) and two concentric (14%) velocities. REX protected angle-specific torque and average power at all velocities. Concentric and eccentric strength decreased at stretched (16%) and neutral (17%) muscle lengths (P < 0.05) in NOE while REX maintained or improved strength at all joint positions. Concentric (15%) and eccentric (11%) contractile work fell in NOE (P < 0.05) but not in REX. Maximal plantar flexor EMG did not change in either group. In summary, constant resistance concentric/eccentric REX completely prevented plantar flexor performance deconditioning induced by BRU. The reported benefits of REX should prove useful in prescribing exercise for astronauts in microgravity and for patients susceptible to functional decline during bed- or chair-bound hospital stays.

Resistance exercise maintains skeletal muscle protein synthesis during bed rest.

Spaceflight results in a loss of lean body mass and muscular strength. A ground-based model for microgravity, bed rest, results in a loss of lean body mass due to a decrease in muscle protein synthesis (MPS). Resistance training is suggested as a proposed countermeasure for spaceflight-induced atrophy because it is known to increase both MPS and skeletal muscle strength. We therefore hypothesized that scheduled resistance training throughout bed rest would ameliorate the decrease in MPS. Two groups of healthy volunteers were studied during 14 days of simulated microgravity. One group adhered to strict bed rest (BR; n = 5), whereas a second group engaged in leg resistance exercise every other day throughout bed rest (BREx; n = 6). MPS was determined directly by the incorporation of infused L-[ring-13C6] phenylalanine into vastus lateralis protein. After 14 days of bed rest, MPS in the BREx group did not change and was significantly greater than in the BR group. Thus moderate-resistance exercise can counteract the decrease in MPS during bed rest.

Resistance exercise training and the orthostatic response.

Resistance exercise has been suggested to increase blood volume, increase the sensitivity of the carotid baroreceptor cardiac reflex response (BARO), and decrease leg compliance, all factors that are expected to improve orthostatic tolerance. To further test these hypotheses, cardiovascular responses to standing and to pre-syncopal limited lower body negative pressure (LBNP) were measured in two groups of sedentary men before and after a 12-week period of either exercise (n = 10) or no exercise (control, n = 9). Resistance exercise training consisted of nine isotonic exercises, four sets of each, 3 days per week, stressing all major muscle groups. After exercise training, leg muscle volumes increased (P < 0.05) by 4-14%, lean body mass increased (P = 0.00) by 2.0 (0.5) kg, leg compliance and BARO were not significantly altered, and the maximal LBNP tolerated without pre-syncope was not significantly different. Supine resting heart rate was reduced (P = 0.03) without attenuating the heart rate or blood pressure responses during the stand test or LBNP. Also, blood volume (125I and 51Cr) and red cell mass were increased (P < 0.02) by 2.8% and 3.9%, respectively. These findings indicate that intense resistance exercise increases blood volume but does not consistently improve orthostatic tolerance.

The effects of albuterol and isokinetic exercise on the quadriceps muscle group.

Subjects performed 9 wk of isokinetic knee extensions twice weekly. Albuterol (N = 13) or placebo (N = 9) was administered for 6 wk; groups received 16 mg.d-1 of either treatment. Training consisted of three sets of 10 repetitions at 45 degrees.s-1. Data were collected at weeks 0, 6, and 9. Concentric and eccentric variables examined included: peak torque (CPT, EPT), total work (CTW, ETW), average power (CAP, EAP), time to peak torque (CTTPT, ETTPT), peak torque to body weight ratio (CPT/BW), and work to body weight ratio (CW/BW, EW/BW). Other variables included: thigh circumference (CIRC), thigh cross-sectional area (CSA), forced vital capacity (FVC), and forced expiratory volume (FEV1), MANOVA and the Dunn-Bonferroni post-hoc found differences within groups for CPT, CTW, CAP, CPR/BW, EPT, ETTPT, and CSA. Interactions were noted for CW/BW, ETW, EAP, EPT/BW, and ETW/BW; with persons administered albuterol yielding superior values. CW/BW, ETW, and EAP showed interactions at post-testing, while EPT/BW and EW/BW interacted at both midtesting and post-testing. Results indicate therapeutic doses of albuterol administered with resistance exercise may augment strength gains.

Changes in body composition, diet, and strength of bodybuilders during the 12 weeks prior to competition.

The purpose of this study was to monitor body composition, diet, and strength in male bodybuilders (No. 6) during the 12 weeks prior to competition. Data were collected every third week and analyzed with repeated measures ANOVA (p < 0.05). Significant decreases (p < 0.01) were found in body mass (-7.3 kg) and hydrostatically determined percent fat (-5.0%), while fat-free mass showed little change. All 7 skinfold sites were reduced significantly (p < 0.01) across the 12 weeks. Ultrasound scan revealed a significant decrease in skin thickness at the biceps (p < 0.01), but no change in biceps thickness. Circumferences decreased significantly at all sites (p < 0.05) except the chest. The greatest decreases were at the waist (-6.9 cm) and hips (-4.3 cm). Maximal isometric dead-lift force decreased significantly (p < 0.05) across time (-129 N). In comparison to off-season, both higher resistance and aerobic training volumes were found during pre-competition. Nutritional analyses showed significant reductions (p < 0.05) in total kilocalories, protein, fat, and cholesterol intakes. Vitamin and mineral intakes exceeded the RDAs. The data indicate the pre-competition practices were effective in reducing subcutaneous fat stores while maintaining muscle. Finally, the onset of the pre-competition phase resulted in strength loss.

Frequency and volume of resistance training: effect on cervical extension strength.

Quantification of cervical extension (CERV EXT) strength is complicated by the inability to stabilize the torso and isolate the CERV EXT muscles. A newly developed machine designed to stabilize the torso and isolate the CERV EXT muscles was used to evaluate the effect of frequency and volume of resistance training on CERV EXT strength. Fifty men (age, 26 +/- 9 years; height, 174 +/- 16 cm; weight, 74 +/- 9 kg) and 28 women (age, 30 +/- 9 years; height, 152 +/- 32 cm; weight, 62 +/- 7 kg) volunteered to participate. Subjects were randomly stratified to one of four training groups or a control group (CONT, n = 19) that did not train. Each training group exercised for 12 weeks as follows; once per week using one set of dynamic exercise (DYN 1x/wk, n = 14), once per week using one set of DYN and one set of maximal isometric (IM) exercise at eight angles through a 126 degrees-range of CERV EXT (DYN-IM 1x/wk, n = 16), DYN 2x/wk (n = 19), or DYN-IM 2x/wk (n = 10). Maximal IM torque was measured at eight angles initially and after 12 weeks of training. All training groups improved CERV EXT strength (p < or = 0.05) at all angles tested compared to the CONT except for DYN once per week at 0 degree of CERV flexion. A greater increase in strength was found when the groups that trained two times a week were compared to those that trained once per week.(ABSTRACT TRUNCATED AT 250 WORDS)