Francis J. Nagle

The effect of pedaling frequency on glycogen depletion rates in type I and type II quadriceps muscle fibers during submaximal cycling exercise

SummaryThis study was conducted to determine whether the pedaling frequency of cycling at a constant metabolic cost contributes to the pattern of fiber-type glycogen depletion. On 2 separate days, eight men cycled for 30 min at approximately 85% of individual aerobic capacity at pedaling frequencies of either 50 or 100 rev·min−1. Muscle biopsy samples (vastus lateralis) were taken immediately prior to and after exercise. Individual fibers were classified as type I (slow twitch), or type II (fast twitch), using a myosin adenosine triphosphatase stain, and their glycogen content immediately prior to and after exercise quantified via microphotometry of periodic acid-Schiff stain. The 30-min exercise bout resulted in a 46% decrease in the mean optical density (D) of type I fibers during the 50 rev·min−1 condition [0.52 (0.07) to 0.28 (0.04)D units; mean (SEM)] which was not different (P>0.05) from the 35% decrease during the 100 rev · min−1 condition [0.48 (0.04) to 0.31 (0.05)D units]. In contrast, the meanD in type II fibers decreased 49% during the 50 rev·min−1 condition [0.53 (0.06) to 0.27 (0.04) units]. This decrease was greater (P<0.05) than the 33% decrease observed in the 100 rev·min −1 condition [0.48 (0.04) to 0.32 (0.06) units). In conclusion, cycling at the same metabolic cost at 50 rather than 100 rev·min−1 results in greater type II fiber glycogen depletion. This is attributed to the increased muscle force required to meet the higher resistance per cycle at the lower pedal frequency. These data are consistent with the view that force development as opposed to velocity of contraction determines the degree of type II fiber recruitment when the metabolic cost of exercise is held constant.

Aerobic requirements of overground versus treadmill running.

There is general agreement that the oxygen demand of level running is similar for both the treadmill (TM) and overground situations at speeds under 260 m X min-1. However, controversy exists with regard to inclined running. The prevailing view, represented by the ACSM prediction formulas, is that overground hill running is theoretically more costly than inclined treadmill running. This study was designed to investigate the problem from an empirical standpoint. Seven male subjects performed overground and TM running at two grades (0 and 5.7%) over a range of speeds between 136-286 m X min-1. For the outdoor trials, subjects covered a distance of 950 m at a constant pace, and expired gas was collected over the last 150 m. Matching trials were then performed on the treadmill at the same speed and % grade. Regression lines were calculated for speed vs oxygen consumption (VO2). For TM and overground level running, these were: VO2 (ml.kg-1.min-1)= 0.222 X speed (m.min-1) - 1.33 and VO2 (ml.kg-1.min-1) = 0.202 X speed (m.min-1) + 3.21 respectively. The regression lines from TM and overground inclined running were: VO2 (ml.kg-1.min-1) = 0.237 X speed (m.min-1) + 7.53. and VO2 (ml.kg-1.min-1) = 0.233 X speed (m.min-1) + 7.78 respectively. A 2 X 3 X 2 ANOVA revealed that the differences between mean values for VO2 for level TM running vs level overground running and grade TM running vs grade overground running were not statistically significant (0.10 less than P less than 0.25).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic response to graded downhill walking.

Compared with level walking or running, progressive downhill walking or running requires a decreasing energy cost to some minimum where the cost again increases with further decrements in grade. Margaria estimated this minimum occurs at a -9% grade. In this study an attempt was made to more precisely track the energy cost curve in progressive downhill treadmill walking. Ten men, mean age 22.0 +/- 2.5 yr, volunteered as subjects. After VO2max determinations the subjects attended two downhill walking sessions. Each subject performed 14 randomly ordered walking bouts of 6 min in duration, at speeds of 90 and 105 m.min-1. The grades used were 0, -3, -6, -9, -12, -15, and -18%. Gas exchange measurements were obtained by open circuit spirometry during each work bout. Heart rate was monitored continuously and the stride frequency was counted by direct observation during each walking bout. Net VO2 values decreased with decrements in grade to -9, -12% for the respective speeds of 90 and 105 m.min-1. The group mean net VO2 minimums at -9 and -12%, however, were not significantly different (P > 0.05) from the group mean values at -6 and -15% at 90 m.min-1, or between -9 and -15% grades at 105 m.min-1, Group mean net VO2 values at 0, -3, and -18% were significantly different (P < 0.05) from net VO2 values for the other grades at 90 m.min-1 walking. At 105 m.min-1, mean net VO2 values at 0, -3, -6, and -18% were significantly different (P < 0.05) from net VO2 values at the other grades.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular responses to upright isometric handgrip and deadlift in men with coronary artery disease

Isometric exercise is usually discouraged for patients with coronary artery disease (CAD) because of the possible adverse effects of increased blood pressure on left ventricular (LV) function. Cardiovascular and LV responses to upright handgrip and deadlift were compared in 10 normal men (mean age 52 years) and 14 men (mean age 54 years) with documented CAD or myocardial infarction who were in a supervised exercise program. Handgrip and deadlift were each performed at 30% maximal effort for 3 minutes. LV technetium-99m multigated radionuclide angiograms, electrocardiogram and blood pressure were measured during the final 60 seconds. CAD patients had a significantly lower LV ejection fraction at rest (41%) than normal subjects (57%). Both groups showed equal and significant increases in heart rate, systolic and diastolic pressure during handgrip and deadlift. These responses were all significantly greater in both groups during deadlift. No significant changes in LV ejection fraction occurred in either group during handgrip or deadlift. LV wall motion abnormalities were present in 9 of 14 CAD patients at rest and increased with handgrip (11 men) and deadlift (13 men). No LV abnormalities occurred in normal subjects. These data indicate cardiovascular responses are similar in normal and exercise-trained CAD patients during upright submaximal isometric exercise using small or large muscle groups. Radionuclide measurements of global LV function remain stable in both groups, during similar conditions of increased systolic pressure afterload. However, LV wall motion abnormalities are aggravated in CAD patients during isometric exercise.

Carnitine status, plasma lipid profiles, and exercise capacity of dialysis patients: Effects of a submaximal exercise program

Carnitine status, blood lipid profiles, and exercise capacity were evaluated in a combined group of hemodialysis (N = 4) and continuous ambulatory peritoneal dialysis (N = 6) patients before and after an 8-week submaximal exercise program. Maximal aerobic capacity (VO2max) was only 18.5 +/- 5.9 (mean +/- SD) mL O2/kg/min, well below the expected 30 to 35 mL O2/kg/min for age-matched sedentary controls. Plasma short-chain acylated carnitine levels, which were two to three times normal values, were reduced after the exercise program, but the long-chain acylcarnitines were significantly reduced during acute exercise. Muscle biopsies of the vastus lateralis were performed at rest in five patients prior to and after the 8-week exercise program. Total carnitine in skeletal muscle was 3.09 (.076 SD) mumol/g ww, with only 11.3% acylated prior to the exercise program, which was much lower than the 4.25 +/- 1.27 mumol/g ww, with 28.5% acylated in a group of healthy athletic subjects (N = 28). Muscle free carnitine concentrations decreased significantly following the 8-week training period, with only a slight reduction in total carnitine. The percent of acylated carnitine was therefore significantly increased (P less than 0.05) from 11.3% to 25.2% after the experimental period. Pretraining carnitine palmitoyl transferase activity at rest was 0.57 +/- 0.28 nmol palmitoyl carnitine formed/5 min/mg mitochondrial protein, which was not changed by exercise training v 1.80 +/- 0.51 nmol/5 min/mg protein in 28 healthy normals (P less than 0.001). Free fatty acid concentrations were reduced significantly during acute exercise as a result of the exercise training program whereas other plasma lipids were not altered. (ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Metabolism During Exercise in Trained Rats: The Potential Role of Carnitine in the Metabolic Fate of Branched-Chain Amino Acids

The influence of endurance training and an acute bout of exercise on plasma concentrations of free amino acids and the intermediates of branched-chain amino acid (BCAA) metabolism were investigated in the rat. Training did not affect the plasma amino acid levels in the resting state. Plasma concentrations of alanine (Ala), aspartic acid (Asp), asparagine (Asn), arginine (Arg), histidine (His), isoleucine (Ile), leucine (Leu), lysine (Lys), methionine (Met), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), and valine (Val) were significantly lower, whereas glutamate (Glu), glycine (Gly), ornithine (Orn), tryptophan (Trp), tyrosine (Tyr), creatinine, urea, and ammonia levels were unchanged, after one hour of treadmill running in the trained rats. Plasma concentration of glutamine (Glu), the branched-chain keto acids (BCKA) and short-chain acyl carnitines were elevated with exercise. Ratios of plasma BCAA/BCKA were dramatically lowered by exercise in the trained rats. A decrease in plasma-free carnitine levels was also observed. These data suggest that amino acid metabolism is enhanced by exercise even in the trained state. BCAA may only be partially metabolized within muscle and some of their carbon skeletons are released into the circulation in forms of BCKA and short-chain acyl carnitines.

Maximal O2 uptake of boys and girls — ages 14–17

SummaryWhite high school girls (n = 120) and boys (n = 120) aged 14–17 years, selected from 9th, 10th, 11th and 12 grades of a northern, midwest U.S. high school performed running exercise on a motor driven treadmill for determinations of maximal O2 uptake (

Energy exchange in downhill and uphill walking: a calorimetric study

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