Allen C. Parcell

Minimum rest period for strength recovery during a common isokinetic testing protocol.

PURPOSE The intent of this investigation was to determine the minimal time for a between sets rest period during a common isokinetic knee extension strength-testing protocol. Based on a review of the literature, a set was considered a group of four maximal coupled contractions at a specific velocity. METHODS Eleven normal, healthy college-age men underwent unilateral knee extension testing to determine their individual isokinetic peak torque at 60, 120, 180, 240, and 300 degrees.s-1. Velocities were administered in ascending order. Between sets, rest periods of 15, 60, 180, and 300 s were assigned to subjects in a counterbalanced fashion. RESULTS There were no differences in peak torque at the beginning velocity of 60 degrees.s-1 among any of the rest periods. At 120 degrees.s-1, peak torque production during the 15-s rest period trial was similar to 60 s but lower than 180 and 300 s. Peak torques at 180, 240, and 300 degrees.s-1 produced during the 15-s rest period test were significantly lower than measured torques at the same velocities during the 60, 180, and 300-s rest period tests (P < 0.05). There were no differences in peak torque production between the 60, 180, and 300-s rest period tests. CONCLUSION These data demonstrate that during a common isokinetic strength testing protocol a between set rest period of at least 60 s is sufficient for recovery before the next test set.

Effects of strength training and vascular occlusion

The purpose of our study was to determine if vascular occlusion produced an additive effect on muscle hypertrophy and strength performance with high strength training loads. Sixteen physically active men were divided into two groups: high-intensity (HI = 6 RM) and moderate-intensity training (MI = 12 RM). An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow was reduced during the exercise. The left leg served as a control, thus was trained without vascular occlusion. Knee extension 1 RM and quadriceps cross-sectional area (MRI) were evaluated pre- and post-8 weeks of training. We only found a main time effect for both strength gains and quadriceps hypertrophy (p < 0.001). Therefore, we conclude that vascular occlusion in combination with high-intensity strength training does not augment muscle strength or hypertrophy when compared to high-intensity strength training alone.

BALLISTIC STRETCHING INCREASES FLEXIBILITY AND ACUTE VERTICAL JUMP HEIGHT WHEN COMBINED WITH BASKETBALL ACTIVITY

Stretching is often included as part of a warm-up procedure for basketball activity. However, the efficacy of stretching with respect to sport performance has come into question. We determined the effects of 4 different warm-up protocols followed by 20 minutes of basketball activity on flexibility and vertical jump height. Subjects participated in 6 weeks (2 times per week) of warm-up and basketball activity. The warm-up groups participated in ballistic stretching, static stretching, sprinting, or basketball shooting (control group). We asked 3 questions. First, what effect does 6 weeks of warm-up exercise and basketball play have on both flexibility and vertical jump height? We measured sit and reach and vertical jump height before (week -1) and after (week 7) the 6 weeks. Flexibility increased for the ballistic, static, and sprint groups compared to the control group (p < 0.0001), while vertical jump height did not change for any of the groups. Our second question was what is the acute effect of each warm-up on vertical jump height? We measured vertical jump immediately after the warm-up on 4 separate occasions during the 6 weeks (at weeks 0, 2, 4, and 6). Vertical jump height was not different for any group. Finally, our third question was what is the acute effect of each warm-up on vertical jump height following 20 minutes of basketball play? We measured vertical jump height immediately following 20 minutes of basketball play at weeks 0, 2, 4, and 6. Only the ballistic stretching group demonstrated an acute increase in vertical jump 20 minutes after basketball play (p < 0.05). Coaches should consider using ballistic stretching as a warm-up for basketball play, as it is beneficial to vertical jump performance.

Aerobic and resistance exercise sequence affects excess postexercise oxygen consumption.

Excess postexercise oxygen consumption (EPOC) may describe the impact of previous exercise on energy metabolism. Ten males completed Resistance Only, Run Only, Resistance-Run, and Run-Resistance experimental conditions. Resistance exercise consisted of 7 lifts. Running consisted of 25 minutes of treadmill exercise. VO2 was determined during tread-mill exercise and after each exercise treatment. Our findings indicated that treadmill exercise VO2 was significantly higher for Resistance-Run compared with Run-Resistance and Resistance Only at all time intervals. At 10 minutes postexercise, VO2 was greater for Resistance Only and Run-Resistance than for Resistance-Run. At 20 and 30 minutes, VO2 following Resistance Only was significantly greater than following Run Only. In conclusion, EPOC is greatest following Run-Resistance; however, treadmill exercise is more physiologically difficult following resistance exercise. Furthermore, the sequence of resistance and treadmill exercise influences EPOC, primarily because of the effects of resistance exercise rather than the exercise combination. We recommend performing aerobic exercise before resistance exercise when combining them into 1 exercise session.

Prediction of Maximum Oxygen Consumption from Walking, Jogging, or Running.

Abstract The purpose of this study was to develop a submaximal, 1.5-mile endurance test for college-aged students using walking, jogging, or running exercise. College students (N = 101: 52 men, 47 women), ages 18–26 years, successfully completed the 1.5-mile test twice, and a maximal graded exercise test. Participants were instructed to achieve a “somewhat hard” exercise intensity (rating of perceived exertion = 13) and maintain a steady pace throughout each 1.5-mile test. Multiple linear regression generated the following prediction equation: VO2max = 65.404 + 7.707 × gender (1 = male; 0 = female) − 0.159 × body mass (kg) − 0.843 × elapsed exercise time (min; walking, jogging, or running). This equation shows acceptable validity (R = .86, SEE = 3.37 ml•kg1 •min−1) similar to the accuracy of comparable field tests, and reliability (ICC = .93) is also comparable to similar models. The statistical shrinkage is minimal (Rpress = 0.85, SEEpress = 3.51 ml•kg1 •min−1); hence, it should provide comparable results when applied to other similar samples. A regression model (R = .90, and SEE = 2.87 ml•kg1 •min−1) including exercise heart rate was also developed: VO2max = 100.162 + 7.301 × gender (1 = male; 0 = female) − 0.164 × body mass (kg) − 1.273 × elapsed exercise time − 0.156 × exercise heart rate, for those who have access to electronic heart rate monitors. This submaximal 1.5-mile test accurately predicts maximal oxygen uptake (VO2max) without measuring heart rate and is similar to the 1.5-mile run in that it allows for mass testing and requires only a flat, measured distance and a stopwatch. Further, it can accommodate a wide range of fitness levels (from walkers to runners).

Effects of warm-up before eccentric exercise on indirect markers of muscle damage.

PURPOSE To test whether active and passive warm-up conducted before eccentric exercise attenuates clinical markers of muscle damage. METHODS Untrained subjects were exposed to one of five conditions: low-heat passive warm-up (N = 10), high-heat passive warm-up (N = 4), or active warm-up (N = 9), preceding eccentric exercise; eccentric exercise without warm-up (N = 10); or high-heat passive warm-up without eccentric exercise (N = 10). Passive warm-up of the elbow flexors was achieved using pulsed short-wave diathermy, and active warm-up was achieved by concentric contraction. Creatine kinase (CK) activity, strength, range of motion, swelling, and muscle soreness were observed before treatment (baseline) and 24, 48, 72, and 168 h after treatment. RESULTS High-heat passive warm-up without eccentric exercise did not affect any marker of muscle damage and was used as our control group. Markers of muscle damage were not different between groups that did or did not conduct warm-up before eccentric exercise. The active warm-up and eccentric groups exhibited a greater circumferential increase than controls (P < 0.0002), however, that was not observed after passive warm-up. Additionally, the active warm-up group exhibited a greater CK response than controls at 72 h (P < 0.05). The high-heat passive warm-up before eccentric exercise group exhibited significant change from controls at the least number of time points, but due to a small sample size (N = 4), these data should be viewed as preliminary. CONCLUSION Our observations suggest that passive warm-up performed before eccentric exercise may be more beneficial than active warm-up or no warm-up in attenuating swelling but does not prevent, attenuate, or resolve more quickly the other clinical symptoms of eccentric muscle damage as produced in this study.

Skeletal muscle dysfunction in muscle-specific LKB1 knockout mice

Liver kinase B1 (LKB1) is a tumor-suppressing protein that is involved in the regulation of muscle metabolism and growth by phosphorylating and activating AMP-activated protein kinase (AMPK) family members. Here we report the development of a myopathic phenotype in skeletal and cardiac muscle-specific LKB1 knockout (mLKB1-KO) mice. The myopathic phenotype becomes overtly apparent at 30-50 wk of age and is characterized by decreased body weight and a proportional reduction in fast-twitch skeletal muscle weight. The ability to ambulate is compromised with an often complete loss of hindlimb function. Skeletal muscle atrophy is associated with a 50-75% reduction in mammalian target of rapamycin pathway phosphorylation, as well as lower peroxisome proliferator-activated receptor-alpha coactivator-1 content and cAMP response element binding protein phosphorylation (43 and 40% lower in mLKB1-KO mice, respectively). Maximum in situ specific force production is not affected, but fatigue is exaggerated, and relaxation kinetics are slowed in the myopathic mice. The increased fatigue is associated with a 30-78% decrease in mitochondrial protein content, a shift away from type IIA/D toward type IIB muscle fibers, and a tendency (P=0.07) for decreased capillarity in mLKB1-KO muscles. Hearts from myopathic mLKB1-KO mice exhibit grossly dilated atria, suggesting cardiac insufficiency and heart failure, which likely contributes to the phenotype. These findings indicate that LKB1 plays a critical role in the maintenance of both skeletal and cardiac function.

Effects of precooling on thermoregulation during subsequent exercise

PURPOSE The purpose of this study was to examine the effect of a decreased body core temperature before a simulated portion of a triathlon (swim,15 min; bike, 45 min) and examine whether precooling could attenuate thermal strain and increase subjective exercise tolerance in a warm environment (26.6 degrees C/60% relative humidity (rh)). METHODS Six endurance trained triathletes (28+/-2 yr, 8.2+/-1.7% body fat) completed two randomly assigned trials 1 wk apart. The precooling trial (PC) involved lowering body core temperature (-0.5 degrees C rectal temperature, Tre) in water before swimming. The control trial (CON) was identical except no precooling was performed. Water temperature and environmental conditions were maintained at 25.6 degrees C and 26.6 degrees C/60% rh, respectively, throughout all testing. RESULTS Mean time to precool was 31+/-8 min and average time to reach baseline Tre during cycling was 9+/-7 min. Oxygen uptake (VO2), HR, skin temperature (Tsk), Tre, RPE, and thermal sensation (TS) were recorded following the swim segment and throughout cycling. No significant differences in mean body (Tb) or Tsk were noted between PC and CON, but a significant difference (P < 0.05) in Tre between treatments was noted through the early phases of cycling. No significant differences were reported in HR, VO2, RPE, TS, or sweat rate (SR) between treatments. Body heat storage (S) was negative following swimming in both PC (-92+/-6 W x m2) and CON (-66+/-9 W x m2). A greater S occurred in PC (109+/-6 W x m2) vs CON (79+/-4 W x m2) during cycling (P < 0.05). CONCLUSIONS Precooling attenuated the rise in Tre, but this effect was transient. Therefore, precooling is not recommended before a triathlon under similar environmental conditions.

Satellite cell activity is differentially affected by contraction mode in human muscle following a work-matched bout of exercise.

Optimal repair and adaptation of skeletal muscle is facilitated by resident stem cells (satellite cells). To understand how different exercise modes influence satellite cell dynamics, we measured satellite cell activity in conjunction with markers of muscle damage and inflammation in human skeletal muscle following a single work- and intensity-matched bout of eccentric (ECC) or concentric contractions (CON). Participants completed a single bout of ECC (n = 7) or CON (n = 7) of the knee extensors. A muscle biopsy was obtained before and 24 h after exercise. Functional measures and immunohistochemical analyses were used to determine the extent of muscle damage and indices of satellite cell activity. Cytokine concentrations were measured using a multiplexed magnetic bead assay. Isokinetic peak torque decreased following ECC (p < 0.05) but not CON. Greater histological staining of the damage marker Xin was observed in muscle samples of ECC vs. CON. Tenasin C immunoreactivity increased 15 fold (p < 0.01) following ECC and was unchanged following CON. The inflammatory cytokines interferon gamma-induced protein 10 (IP-10) and monocyte chemotactic protein 1 (MCP-1) increased pre- to post-ECC (4.26 ± 1.4 vs. 10.49 ± 5.8 pg/ml, and 3.06 ± 0.7 vs. 6.25 ± 4.6 pg/ml, respectively; p < 0.05). There was no change in any cytokine post-CON. Satellite cell content increased 27% pre- to post-ECC (0.10 ± 0.031 vs. 0.127 ± 0.041, respectively; p < 0.05). There was no change in satellite cell number in CON (0.099 ± 0.027 vs. 0.102 ± 0.029, respectively). There was no fiber type-specific satellite cell response following either exercise mode. ECC but not CON resulted in an increase in MyoD positive nuclei per myofiber pre- to post-exercise (p < 0.05), but there was no change in MyoD DNA binding activity in either condition. In conclusion, ECC but not CON results in functional and histological evidence of muscle damage that is accompanied by increased satellite cell activity 24 h post-exercise.

Single muscle fiber myosin heavy chain distribution in elite female track athletes.

PURPOSE Myosin heavy chain (MHC) characterization of tissue samples from the gastrocnemius muscle of six elite female athletes and 10 untrained females was performed using myosin ATPase histochemistry and gel electrophoresis. Athletes were of national and international caliber, whereas their untrained counterparts were healthy individuals not involved in a regular exercise program. METHODS Muscle biopsies for the athletes were performed 14 wk into their training season and analyzed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and myosin ATPase techniques. RESULTS Electrophoretic analysis of single muscle fibers from elite athletes revealed a MHC phenotype composition of 46 +/- 6% type I, 21 +/- 6% type IIa, and 0% type IIx, whereas 34% of the single fibers expressed multiple MHC isoforms. When compared with the elite women, untrained subjects demonstrated higher percentages of type I MHC and lower percentages of IIa MHC muscle fibers, 57 +/- 5 and 16 +/- 3%, respectively (P < 0.05). Similar to the female athletes, 27% of the fibers from untrained women possessed multiple myosin isoforms. Myosin ATPase staining demonstrated a greater percentage of type I fibers in untrained subjects versus the elite women (67 +/- 3 vs 41 +/- 2%, P< 0.05) (mean +/- SE), whereas the athletes had a higher percentage of type IIa fibers compared with the untrained women (49 +/- 5 vs 19 +/- 2%, P< 0.05). There were no differences in the percentage of IIb fibers between elite and untrained women (11 +/- 4 vs 14 +/- 2%, respectively). CONCLUSIONS Whereas a preponderance of hybrid fibers is generally observed in untrained populations, the diverse MHC phenotype seen in these elite female athletes is uncommon. These unique findings are attributed to the chronic and varied nature of training in which these athletes were involved.