Multivariate genetic analysis of maximal isometric muscle force at different elbow angles

Thomis, Martine A., Marc Van Leemputte, Hermine H. Maes,Cameron J. R. Blimkie, Albrecht L. Claessens, Guy Marchal, Eustachius Willems, Robert F. Vlietinck, and Gaston P. Beunen. Multivariate genetic analysis of maximal isometric muscle force at different elbowangles. J. Appl. Physiol. 82(3):959-967, 1997.The maximal isometric moment at five differentelbow joint angles was measured in 25 monozygotic and 16 dizygotic maleadult twin pairs (22.4 ± 3.7 yr). Genetic model fittingwas used to quantify the genetic and environmental contributions toindividual differences in isometric strength. Additive genetic factorsexplained 66-78% of the variance in maximal torque at170-140-110 and 80° flexion (extension = 180°). At50° flexion, common and subject-specific environmental factorscontributed equally to the variation. The contribution of uniqueenvironmental factors concurs with the level of variability in muscleactivation and (dis)-comfort of torque production in the specificangle. The relative contribution of lever arm and force-lengthrelationship in torque varies according to the angle. Because thesefactors might be genetic, this variability is reflected in the geneticcontribution at the extreme angles of 170 and 50°. Multivariateanalyses suggested a general set of genes that control muscle area andisometric strength, together with a more specific strength factor.Genetic correlations were high (0.82-0.99). Genes responsible forarm-segment lengths did not contribute to muscle area nor to isometricstrength.

     

Age and gender interactions in physiological functional capacity: insight from swimming performance

Tanaka, Hirofumi, and Douglas R. Seals. Age and genderinteractions in physiological functional capacity: insight from swimming performance. J. Appl.Physiol. 82(3): 846-851, 1997.One experimentalapproach to studying the effects of aging on physiological functionalcapacity in humans is to analyze the peak exercise performance ofhighly trained athletes with increasing age. To gain insight into therelationships among age, gender, and exercise task duration with use ofthis model, we performed a 5-yr (1991-1995) retrospective analysisof top freestyle performance times from the US Masters SwimmingChampionships. Regression analysis showed that in both men and womenendurance swimming performance (i.e., 1,500 m) declined linearly frompeak levels at age 35-40 yr until ~70 yr of age, whereuponperformance declined exponentially thereafter. In both genders, thevariability among the top 10 winning times in each 5-yr age intervalincreased markedly with advancing age. Compared with the 1,500-mfreestyle, performance in the 50-m freestyle (short-duration task)showed only a modest decline until ages 75 and 80 yr in women and men,respectively. The rate and magnitude of the declines in both short- andlong-duration swimming performance with age were significantly(P < 0.05) greater in women than in men. In the women, the percent decline in swimming performance over a50-yr age period from the 19- to 24-yr to the 69- to 74-yr age groupsbecame progressively greater from the shortest distance (50 m) to thetwo longest distances (800 and 1,500 m), whereas in men, no differenceswere observed in the magnitude of performance decline with age amongthe five longest distance events (i.e., 100-1,500 m). The percentgender difference in performance throughout the age range studiedbecame progressively smaller (P < 0.05) with increasing distance from 50 m (19 ± 1%) to 1,500 m (11 ± 1%). The findings in this cross-sectional study indicate that from peak levels at age 35-40 yr, physiological functionalcapacity, as assessed by swimming performance, decreases linearly until ~70-80 yr of age, whereupon the decline becomes exponential.Moreover, the rate of decline with advancing age appears to beassociated with event duration and gender.

     

Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter

Pedersen, O. F., T. F. Pedersen, and M. R. Miller. Gascompression in lungs decreases peak expiratory flow depending onresistance of peak flowmeter. J. Appl.Physiol. 83(5): 1517-1521, 1997.It has recentlybeen shown (O. F. Pedersen T. R. Rasmussen, Ø. Omland, T. Sigsgaard, P. H. Quanjer, and M. R. Miller. Eur. Respir. J. 9: 828-833, 1996) that the addedresistance of a mini-Wright peak flowmeter decreases peak expiratoryflow (PEF) by ~8% compared with PEF measured by a pneumotachograph.To explore the reason for this, 10 healthy men (mean age 43 yr, range33-58 yr) were examined in a body plethysmograph with facilitiesto measure mouth flow vs. expired volume as well as the change inthoracic gas volume (Vb) and alveolar pressure(PA). The subjects performed forced vital capacity maneuvers through orifices of different sizes andalso a mini-Wright peak flowmeter. PEF with the meter and other addedresistances were achieved when flow reached the perimeter of theflow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 ± 1.5 to 10.3 ± 1.4 (SD) l/s(P < 0.001),PA increased from 6.7 ± 1.9 to 9.3 ± 2.7 kPa (P < 0.001), anincrease equal to the pressure drop across the meter, and caused Vb atPEF to decrease by 0.24 ± 0.09 liter(P < 0.001). We conclude that PEF obtained with an added resistance like a mini-Wright PEF meter is awave-speed-determined maximal flow, but the added resistance causes gascompression because of increasedPA at PEF. Therefore, Vb at PEFand, accordingly, PEF decrease.

     

Age and gender comparisons of muscle strength in 654women and men aged 20-93 yr

Lindle, R. S., E. J. Metter, N. A. Lynch, J. L. Fleg, J. L. Fozard, J. Tobin, T. A. Roy, and B. F. Hurley. Age and gendercomparisons of muscle strength in 654 women and men aged 20-93 yr.J. Appl. Physiol. 83(5): 1581-1587, 1997.To assess ageand gender differences in muscle strength, isometric, concentric (Con),and eccentric (Ecc) peak torque was measured in the knee extensors at aslow (0.52 rad/s) and fast (3.14 rad/s) velocity in 654 subjects (346 men and 308 women, aged 20-93 yr) from the Baltimore LongitudinalStudy of Aging. Regression analysis revealed significant(P < 0.001) age-related reductions in Con and Ecc peaktorque for men and women at both velocities, but no differences wereobserved between the gender groups or velocities. Age explained lossesin Con better than Ecc peak torque, accounting for 30% (Con) vs. 19%(Ecc) of the variance in men and 28% (Con) vs. 11% (Ecc) in women. Toassess age and gender differences in the ability to store and utilizeelastic energy, the stretch-shortening cycle was determined in a subsetof subjects (n = 47). The older women (mean age = 70 yr)showed a significantly greater enhancement in the stretch-shorteningcycle, compared with men of similar age (P < 0.01) andcompared with younger men and women (each P < 0.05). Bothmen and women showed significant declines in muscle quality for Conpeak torque (P < 0.01), but no gender differences were observed. Only the men showed a significant decline in muscle quality(P < 0.001) for Ecc peak torque. Thus both men and women experience age-related losses in isometric, Con, and Ecc knee extensorpeak torque; however, age accounted for less of the variance in Eccpeak torque in women, and women tend to better preserve muscle qualitywith age for Ecc peak torque. In addition, older women have an enhancedcapacity to store and utilize elastic energy compared with similarlyaged men as well as with younger women and men.

     

Blood pressure risk factors in healthy postmenopausal women: physical activity and hormone replacement

Stevenson, Edith T., Kevin P. Davy, Pamela P. Jones,Christopher A. Desouza, and Douglas R. Seals. Blood pressure risk factors in healthy postmenopausal women: physical activity and hormonereplacement. J. Appl. Physiol. 82(2):652-660, 1997.The prevalence of cardiovascular disease (CVD)increases with advancing age in women, particularly after menopause.CVD risk is lower in physically active women relative to theirsedentary peers, but the responsible mechanisms are not wellunderstood. The aims of this study were to test the hypotheses that1) physically active postmenopausalwomen demonstrate more favorable blood pressure (BP)-related riskfactors for CVD than do sedentary healthy women and2) women on hormone replacementtherapy (HRT) also have more favorable levels of these CVD riskfactors. BP-related CVD risk factors were measured in physically activewomen (n = 18; age 55 ± 1 yr;n = 8 on HRT) and in healthyless-active controls (n = 34; age 59 ± 1 yr; n = 17 on HRT). Maximaloxygen consumption was higher in the active group, whereas waist-to-hipratio and waist circumference were lower (allP < 0.005). The activewomen demonstrated marginally lower (5-8 mmHg;P  0.10) levels of casual, 24-h, anddaytime systolic BP (SBP). They also tended to have lower(P = 0.11) daytime SBP loads(percentage of BP recordings >140/90 mmHg) and lower daytime andnighttime BP variabilities (P = 0.04)and a reduced (P < 0.007) SBPresponse to submaximal exercise. Women on HRT tended to have lower(3-4 mmHg; P = 0.07) levels of24-h and nighttime diastolic BP (DBP) relative to the nonusers andsmaller (P < 0.04) daytime and 24-hDBP loads. Stepwise multiple regression indicated that waistcircumference was the primary predictor of most of the SBP-related CVDrisk factors while HRT use was the best predictor for DBP loads. Thesefindings indicate that, in general, physically active postmenopausalwomen demonstrate more favorable SBP-related CVD risk factors relative to their less-active healthy peers, which may be mediated, in part, bytheir lower levels of abdominal adiposity. In addition, HRT use tendsto be associated with lower levels of DBP-related CVD risk factors.

     

Age and gender dependency of baroreflex sensitivity in healthy subjects

Laitinen, Tomi, Juha Hartikainen, Esko Vanninen, LeoNiskanen, Ghislaine Geelen, and Esko Länsimies. Age andgender dependency of baroreflex sensitivity in healthy subjects.J. Appl. Physiol. 84(2): 576-583, 1998.We evaluated the correlates of baroreflex sensitivity (BRS) inhealthy subjects. The study consisted of 117 healthy, normal-weight,nonsmoking male and female subjects aged 23-77 yr. Baroreflexcontrol of heart rate was measured by using the phenylephrinebolus-injection technique. Frequency- and time-domain analysis of heartrate variability and an exercise test were performed. Plasmanorepinephrine, epinephrine, insulin, and arginine vasopressinconcentrations and plasma renin activity were measured. In theunivariate analysis, BRS correlated with age(r = 0.65,P < 0.001), diastolic blood pressure(r = 0.47, P < 0.001), exercise capacity(r = 0.60, P < 0.001), and the high-frequency component of heart rate variability (r = 0.64, P < 0.001). There was also asignificant correlation between BRS and plasma norepinephrine concentration (r = 0.22,P < 0.05) and plasma renin activity (r = 0.32, P < 0.001). According to themultivariate analysis, age and gender were the most importantphysiological correlates of BRS. They accounted for 52% ofinterindividual BRS variation. In addition, diastolic blood pressureand high-frequency component of heart rate variability were significantindependent correlates of BRS. BRS was significantly higher in men thanin women (15.0 ± 1.2 vs. 10.2 ± 1.1 ms/mmHg, respectively;P < 0.01). Twenty-four percent ofwomen >40 yr old and 18% of men >60 yr old had markedly depressedBRS (<3 ms/mmHg). We conclude that physiological factors, particularly age and gender, have significant impact on BRS in healthysubjects. In addition, we demonstrate that BRS values that have beenproposed to be useful in identifying postinfarction patients at highrisk of sudden death are frequently found in healthy subjects.

     

Twenty-year follow-up of aerobic power and body composition of older track athletes

Pollock, Michael L., Larry J. Mengelkoch, James E. Graves,David T. Lowenthal, Marian C. Limacher, Carl Foster, and Jack H. Wilmore. Twenty-year follow-up of aerobic power and body composition of older track athletes. J. Appl.Physiol. 82(5): 1508-1516, 1997.The purpose wasto determine the aerobic power (maximal oxygen uptake) and bodycomposition of older track athletes after a 20-yr follow-up (T3). At 20 yr, 21 subjects [mean ages: 50.5 ± 8.5 yr at initialevaluation (T1), 60.2 ± 8.8 yr at 10-yr follow-up (T2), and 70.4 ± 8.8 yr at 20-yr follow-up (T3)] were divided into threeintensity groups: high (H; remained elite; n = 9); moderate (M; continuedfrequent moderate-to-rigorous endurance training;n = 10); and low (L; greatly reducedtraining; n = 2). All groupsdecreased in maximal oxygen uptake at each testing point (H, 8 and15%; M, 13 and 14%; and L, 18 and 34% from T1 to T2 and T2 to T3,respectively). Maximal heart rate showed a linear decrease of~5-7beats · min¹ · decade¹ and was independentof training status. Body weight remained stable for the H and M groupsand percent fat increased ~2-2.5%/decade. Although fat-freeweight decreased at each testing point, there was a trend for those whobegan weight-training exercise to better maintain it. Cross-sectionalanalysis at T3 showed that leg strength and bone mineral density weregenerally maintained from age 60 to 89 yr. Those who performed weighttraining had a greater arm region bone mineral density than those whodid not. These longitudinal data show that the physiological capacitiesof older athletes are reduced despite continued vigorous enduranceexercise over a 20-yr period (~8-15%/decade). Changes in bodycomposition appeared to be less than those shown for the healthysedentary population and were related to changes in training habits.

     

Angiogenesis in bronchial circulatory system after unilateral pulmonary artery obstruction

Charan, Nirmal B., and Paula Carvalho. Angiogenesis inbronchial circulatory system after unilateral pulmonary artery obstruction. J. Appl. Physiol. 82(1):284-291, 1997.We studied the effects of left pulmonary artery(LPA) ligation on the bronchial circulatory system (BCS) by using asheep model. LPA was ligated in the newborn lambs soon after birth(n = 8), and when the sheep were ~3yr of age anatomic studies revealed marked angiogenesis in BCS.Bronchial blood flow and cardiac output were studied by placing flowprobes around the bronchial and pulmonary arteries in four adult sheep.After LPA ligation, bronchial blood flow increased from 35 ± 6 to134 ± 42 ml/min in ~3 wk (P < 0.05). We also studied gas-exchange functions of BCS ~3 yr after the ligation of LPA in newborn lambs (n = 4) and used a control group (n = 12)in which LPA was ligated acutely. In the left lung,O₂ uptake after acute ligation was16 ± 3 ml/min and was similar to the chronic model, whereasCO₂ output in the control group was 27 ± 3 ml/min compared with 79 ± 12 ml/min in the chronic preparation (P < 0.05).We conclude that LPA ligation causes marked angiogenesis in BCS that iscapable of performing some gas-exchange functions.

     

Reproductive function in male endurance athletes: sperm analysis and hormonal profile

Lucía, Alejandro, José L. Chicharro, MargaritaPérez, Luis Serratosa, Fernando Bandrés, and Julio C. Legido. Reproductive function in male endurance athletes: spermanalysis and hormonal profile. J. Appl.Physiol. 81(6): 2627-2636, 1996.The purpose ofthis investigation was to study the effects of endurance exercise onmale reproductive function (sex hormones and seminograms). Professionalcyclists [n = 12; mean age 24 ± 2 (SD) yr], elite triathletes(n = 9; 26 ± 3 yr),recreational marathon runners (n = 10;32 ± 6 yr), and sedentary subjects (control group;n = 9; 30 ± 4 yr) were selected assubjects. For each group, the following parameters were measured threetimes during the sports season (training period: winter; competitionperiod: spring; resting period: fall): percentage of body fat, hormonalprofile (resting levels of follicle-stimulating hormone, luteinizinghormone, total and free testosterone, and cortisol), and seminograms(quantitative parameters: sperm volume and sperm count; qualitativeparameters: sperm motility and morphology). The following comparisonswere made in the measured parameters:1) within groups (longitudinal design) and 2) between groups ineach of the three periods (cross-sectional design) and over time (mixeddesign). In addition, both the volume and the intensity of training ofeach subject during the season (except for the control group) werequantified. Despite significant differences in training characteristicsand in body fat percent, in general no significant differences(P > 0.05) were found in hormonalprofiles or in semen characteristics between or within groups. A lowersperm motility (46.2 ± 19.5%), however, was observed in thecyclists during the competition period when compared either with theother groups during this same period(P < 0.05) or with themselves duringthe other two periods of study (P < 0.01). In any case, the later phenomenon was attributed to physicalfactors associated with cycling, such as mechanical trauma to thetestis and/or increased gonadal temperature. In conclusion, ourfindings suggest that endurance exercise does not adversely affect the hypothalamic-pituitary-testis axis.

     

Hemodynamic correlates of effective arterial elastance in mitral stenosis before and after balloon valvotomy

Colin, Patrice, Michel Slama, Alec Vahanian, YvesLecarpentier, Gilbert Motté, and Denis Chemla. Hemodynamiccorrelates of effective arterial elastance in mitral stenosis beforeand after balloon valvotomy. J. Appl.Physiol. 83(4): 1083-1089, 1997.This study hadthe purpose of documenting the hemodynamic correlates of effectivearterial elastance (Ea; i.e., an accurate estimate of hydraulic load)in mitral stenosis (MS) patients. The main hypothesis tested was thatEa relates to the total vascular resistance (R)-to-pulse intervalduration (T) ratio(R/T) in MS patients both before andafter successful balloon mitral valvotomy (BMV). High-fidelity aorticpressure recordings were obtained in 10 patients (40 ± 12 yr)before and 15 min after BMV. Ea value was calculated as the ratio ofthe steady-state end-systolic aortic pressure (ESAP) to stroke volume(thermodilution). Ea increased after BMV (from 1.55 ± 0.63 to 1.83 ± 0.71 mmHg/ml; P < 0.05). Throughout the procedure, there was a strong linearrelationship between Ea and R/T: Ea = 1.09R/T  0.01 mmHg/ml,r = 0.99, P = 0.0001. This ultimately dependedon the powerful link between ESAP and mean aortic pressure [MAP;r = 0.99, 95% confidence interval for the difference (MAP  ESAP) from 18.5 to +4.5 mmHg].Ea was also related to total arterial compliance (area method) and towave reflections (augmentation index), although to a lesser extent. After BMV, enhanced and anticipated wave reflections were observed, andthis was likely to be explained by decreased arterial compliance. Thepresent study indicated that Ea depended mainly on the steady componentof hydraulic load (i.e., R) and on heart period (i.e., T) in MS patients.

     

Muscle quality. I.Age-associated differences between arm and leg muscle groups

To determine the differences between armand leg muscle quality (MQ) across the adult life span in men andwomen, concentric (Con) and eccentric (Ecc) peak torque (PT) weremeasured in 703 subjects (364 men and 339 women, age range 19-93yr) and appendicular skeletal muscle mass (MM) was determined in thearm and leg in a subgroup of 502 of these subjects (224 men and 278 women). Regression analysis showed that MQ, defined as PT per unit ofMM, was significantly higher in the arm (~30%) than in the legacross age in both genders (P < 0.01). Arm and leg MQ declined at a similar rate with age in men,whereas leg MQ declined ~20% more than arm MQ with increasing age inwomen (P  0.01 andP < 0.05 for Con and Ecc PT,respectively). Moreover, the age-associated decrease in arm MQ wassteeper in men than in women whether Con or Ecc PT was used (bothP < 0.05). Arm MQ as determined byCon PT showed a linear age-related decline in men and women (28 and20%, respectively, P < 0.001),whereas arm MQ as determined by Ecc PT showed a linear age-relateddecline in men (25%, P < 0.001) butnot in women (not significant). In contrast, both genders exhibited anage-related quadratic decline in leg MQ as determined by Con PT(~40%) and Ecc PT (~25%; both P < 0.001), and the rate of decline was similar for men and women. ThusMQ is affected by age and gender, but the magnitude of this effectdepends on the muscle group studied and the type of muscle action (Convs. Ecc) used to assess strength.

     

Age-related changes in the twitch contractile properties of human thenar motor units

Doherty, Timothy J., and William F. Brown. Age-relatedchanges in the twitch contractile properties of human thenar motorunits. J. Appl. Physiol. 82(1):93-101, 1997.The purpose of this study was to examine theeffects of aging on the contractile and electrophysiological propertiesof human thenar motor units (MUs). Percutaneous electrical stimulationof single motor axons within the median nerve was used to isolate andexamine the twitch tensions, contractile speeds, and surface-detectedMU action potential (S-MUAP) sizes of 48 thenar MUs in 17 youngersubjects (25-53 yr) and 44 thenar MUs in 9 older subjects(64-77 yr). A wide range of twitch tensions, contractile speeds,and S-MUAP sizes was observed in both age groups. However, oldersubjects had significantly larger MU twitch tensions and slower MUtwitch contraction and half-relaxation times. These changes wereaccompanied by increased S-MUAP sizes. These findings suggest that thehuman thenar MU pool undergoes significant age-related increase in MUsize and slowing of contractile speed. Such adaptation may help toovercome previously reported age-related losses of thenar MUs.

     

A 33-yr follow-up of peak oxygen uptake and related variables of former physical education students

Åstrand, Per-Olof, Ulf Bergh, and ÅsaKilbom. A 33-yr follow-up of peak oxygen uptake and relatedvariables of former physical education students. J. Appl. Physiol. 82(6): 1844-1852, 1997.In 1949, 27 female and 26 male physical education students were studied at amean age of 22 and 25 yr, respectively. They were restudied in 1970 and1982. Measurements included oxygen uptake, heart rate, and pulmonaryventilation during submaximal and maximal exercise on a cycle ergometerand treadmill. After 21 yr, peak aerobic power was significantlyreduced, from 2.90 to 2.18 l/min and from 4.09 to 3.28 l/min for womenand men, respectively. After another 12 yr, the 1970 maxima were notreduced further. From 1949 to 1982 there was a decrease in peak heartrate from 196 to 177 beats/min in women and from 190 to 175 beats/minin men (P < 0.05). Highest pulmonaryventilation did not change significantly. At an oxygen uptake of 1.5 l/min, the heart rate was the same in 1949 as in 1982. In conclusion,the physical fitness level of the subjects was well above average forthese ages. From 1970 to 1982 there was no decline in the average peakaerobic power, a finding possibly related to increased habitualphysical activity.

     

Are basal metabolic rate prediction equations appropriate for female children and adolescents?

Wong, William W., Nancy F. Butte, Albert C. Hergenroeder,Rebecca B. Hill, Janice E. Stuff, and E. O'Brian Smith. Are basalmetabolic rate prediction equations appropriate for female children andadolescents? J. Appl. Physiol. 81(6):2407-2414, 1996.The basal metabolic rate (BMR), which accountsfor 50-70% of total energy expenditure, is essential forestimation of patient and population energy needs. Numerous equationshave been formulated for prediction of human BMR. Most equations incurrent use are based on measurements of Caucasians performed more thanfour decades ago. We evaluated 10 prediction equations commonly usedfor estimation of BMR in 76 Caucasian and 42 African-American girlsbetween 8 and 17 yr of age against BMR measured by whole-bodycalorimetry. The majority of the prediction equations (9 of10) overestimated BMR by 60 ± 46 kcal/day (range,15-176 kcal/day). This overestimation was found to besignificantly greater (P < 0.05) forAfrican-Americans (77 ± 17 kcal/day) than for Caucasians (25 ± 17 kcal/day) in six equations, controlling for age, weight, and sexualmaturity. We conclude that ethnicity is an important factor inestimation of the BMR and that the current prediction equations are notappropriate for accurate estimation of the BMR of individual femalechildren and adolescents.

     

Appendicular skeletal muscle mass: effects of age, gender, and ethnicity

Gallagher, Dympna, Marjolein Visser, Ronald E. De Meersman,Dennis Sepúlveda, Richard N. Baumgartner, Richard N. Pierson, Tamara Harris, and Steven B. Heymsfield. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J. Appl. Physiol. 83(1): 229-239, 1997.This studytested the hypothesis that skeletal muscle mass is reduced in elderlywomen and men after adjustment first for stature and body weight. Thehypothesis was evaluated by estimating appendicular skeletal musclemass with dual-energy X-ray absorptiometry in a healthy adult cohort. Asecond purpose was to test the hypothesis that whole body⁴⁰K counting-derived total bodypotassium (TBK) is a reliable indirect measure of skeletal muscle mass.The independent effects on both appendicular skeletal muscle and TBK ofgender (n = 148 women and 136 men) andethnicity (n = 152 African-Americans and 132 Caucasians) were also explored. Main findingswere 1) for both appendicularskeletal muscle mass (total, leg, and arm) and TBK, age was anindependent determinant after adjustment first by stepwise multipleregression for stature and weight (multiple regression modelr² = ~0.60);absolute decrease with greater age in men was almost double that inwomen; significantly larger absolute amounts were observed in men andAfrican-Americans after adjustment first for stature, weight, and age;and >80% of within-gender or -ethnic group between-individualcomponent variation was explained by stature, weight, age, gender, andethnicity differences; and 2) mostof between-individual TBK variation could be explained by totalappendicular skeletal muscle(r² = 0.865),whereas age, gender, and ethnicity were small but significant additional covariates (totalr² = 0.903). Ourstudy supports the hypotheses that skeletal muscle is reduced in theelderly and that TBK provides a reasonable indirect assessment ofskeletal muscle mass. These findings provide a foundation forinvestigating skeletal muscle mass in a wide range of health-related conditions.

     

Effects of four different single exercise sessions on lipids, lipoproteins, and lipoprotein lipase

The purpose ofthis study was to determine the threshold of exercise energyexpenditure necessary to change blood lipid and lipoproteinconcentrations and lipoprotein lipase activity (LPLA) in healthy,trained men. On different days, 11 men (age, 26.7 ± 6.1 yr; bodyfat, 11.0 ± 1.5%) completed four separate, randomly assigned,submaximal treadmill sessions at 70% maximalO₂ consumption. During eachsession 800, 1,100, 1,300, or 1,500 kcal were expended. Compared withimmediately before exercise, high-density lipoprotein cholesterol(HDL-C) concentration was significantly elevated 24 h after exercise(P < 0.05) in the 1,100-, 1,300-, and 1,500-kcal sessions. HDL-C concentration was also elevated(P < 0.05) immediately after and 48 h after exercise in the 1,500-kcal session. Compared with values 24 hbefore exercise, LPLA wassignificantly greater (P < 0.05) 24 h after exercise in the 1,100-, 1,300-, and 1,500-kcal sessions andremained elevated 48 h after exercise in the 1,500-kcal session. Thesedata indicate that, in healthy, trained men, 1,100 kcal of energyexpenditure are necessary to elicit increased HDL-C concentrations.These HDL-C changes coincided with increased LPLA.

     

Neuromuscular factors contributing to in vivo eccentric moment generation

Webber, Sandra, and Dean Kriellaars. Neuromuscularfactors contributing to in vivo eccentric moment generation.J. Appl. Physiol. 83(1): 40-45, 1997.Muscle series elasticity and its contribution to eccentricmoment generation was examined in humans. While subjects [male,n = 30; age 26.3 ± 4.8 (SD) yr; body mass 78.8 ± 13.1 kg] performed an isometric contractionof the knee extensors at 60° of knee flexion, a quick stretch was imposed with a 12°-step displacement at 100°/s. The test wasperformed at 10 isometric activation levels ranging from 1.7 to 95.2%of maximal voluntary contraction (MVC). A strong linear relationship was observed between the peak imposed eccentric moment derived fromquick stretch and the isometric activation level(y = 1.44x + 7.08; r = 0.99). This increase in theeccentric moment is consistent with an actomyosin-dependent elasticitylocated in series with the contractile element of muscle. Byextrapolating the linear relationship to 100% MVC, the predictedmaximum eccentric moment was found to be 151% MVC, consistent with invitro data. A maximal voluntary, knee extensor strength test was alsoperformed (5-95°, 3 repetitions, ±50, 100, 150, 200, and250°/s). The predicted maximum eccentric moment was 206% of theangle- and velocity-matched, maximal voluntary eccentric moments. Thiswas attributed to a potent neural regulatory mechanism that limits therecruitment and/or discharge of motor units during maximalvoluntary eccentric contractions.

     

Cerebral areas associated with motor control of speech in humans

Murphy, K., D. R. Corfield, A. Guz, G. R. Fink, R. J. S. Wise, J. Harrison, and L. Adams. Cerebral areas associated withmotor control of speech in humans. J. Appl.Physiol. 83(5): 1438-1447, 1997.We have definedareas in the brain activated during speaking, utilizing positronemission tomography. Six normal subjects continuously repeated thephrase "Buy Bobby a poppy" (requiring minimal languageprocessing) in four ways: A) spoken aloud, B) mouthed silently,C) without articulation, andD) thought silently. Statisticalcomparison of images from conditions Awith C andB withD highlighted areas associated witharticulation alone, because control of breathing for speech wascontrolled for; we found bilateral activations in sensorimotor cortexand cerebellum with right-sided activation in the thalamus/caudate nucleus. Contrasting images from conditionsA with B andC with D highlighted areas associated withthe control of breathing for speech, vocalization, and hearing, becausearticulation was controlled for; we found bilateral activations insensorimotor and motor cortex, close to but distinct from theactivations in the preceding contrast, together with activations inthalamus, cerebellum, and supplementary motor area. In neithersubtraction was there activation in Broca's area. These resultsemphasize the bilaterality of the cerebral control of "speaking"without language processing.

     

Physiological adaptations to a weight-loss dietary regimen and exercise programs in women

Kraemer, William J., Jeff S. Volek, Kristine L. Clark, ScottE. Gordon, Thomas Incledon, Susan M. Puhl, N. Travis Triplett-McBride, Jeffrey M. McBride, Margot Putukian, and Wayne J. Sebastianelli. Physiological adaptations to a weight-loss dietary regimen andexercise programs in women. J. Appl.Physiol. 83(1): 270-279, 1997.Thirty-one women(mean age 35.4 ± 8.5 yr) who were overweight were matched andrandomly placed into either a control group (Con; n = 6), a diet-only group (D;n = 8), a diet+aerobic endurance exercise training group (DE; n = 9),or a diet+aerobic endurance exercise training+strength training group(DES; n = 8). After 12 wk, the threedietary groups demonstrated a significant(P  0.05) reduction in body mass,%body fat, and fat mass. No differences were observed in the magnitudeof loss among groups, in fat-free mass, or in resting metabolic rate.The DE and DES groups increased maximal oxygen consumption, and the DESgroup demonstrated increases in maximal strength. Weight loss resultedin a similar reduction in total serum cholesterol, low-densitylipoprotein cholesterol, and high-density lipoprotein cholesterol amongdietary groups. These data indicate that weight loss during moderatecaloric restriction is not altered by inclusion of aerobic oraerobic+resistance exercise, but diet in conjunction with training caninduce remarkable adaptations in aerobic capacity and muscular strengthdespite significant reductions in body mass.

     

Time course of recovery from nerve injury in skeletal muscle: energy state and local circulation

Hayashi, Yoshihiro, Takaaki Ikata, Hiroaki Takai, ShinjiroTakata, Takayuki Sogabe, and Keiko Koga. Time course of recoveryfrom nerve injury in skeletal muscle: energy state and localcirculation. J. Appl. Physiol. 82(3):732-737, 1997.This study examined the time course of recoveryfrom nerve injury on energy state assessed by phosphorus-31 magneticresonance spectroscopy and local circulation dynamics by fluorine-19magnetic resonance spectroscopy in skeletal muscles ofrats. The hindlimb muscles that had undergone unilateralsciatic nerve compression for 2 wk (CN) were compared withsham-operated (SO) muscles and with muscles that had the compressionremoved after 2 wk and were allowed to recover for 4 wk (R4) or for 6 wk (R6). The energy state and local circulation dynamics of CN muscleswere less than those of SO muscles (P < 0.01). The energy state of R4 muscles remained at levels similar toCN muscles, whereas the local circulation dynamics improved but notback to SO values. In R6 muscles, both parameters returned to SOvalues. These results showed that the recovery processes of circulationprecede those of energy state in skeletal muscles.