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Biomedical subjects

P W Lemon

Publications and source records attributed to P W Lemon.

33 records · Page 2Linked to original sources
PubMed1989

Effect of chronic endurance exercise on retention of dietary protein.

On two separate occasions, five well-trained endurance runners (VO2max = 71 +/- 5 ml/kg/min; means +/- SD) consumed a meat-free diet for 6 days. For one trial the subjects consumed the recommended dietary allowance (RDA) of protein (REC-PRO = 0.86 +/- 0.23 g/kg body wt/day). Protein intake for the other trial was 1.7 times higher (HI-PRO = 1.49 +/- 0.29 g/kg body wt/day). Each subject followed his regular training program (12-16 km running/day), and on day 5 of each diet completed a treadmill run at a similar intensity and duration (75 min at 72% VO2max). Seventy-two hour urinary urea N loss (days 4, 5, and 6 of each diet) and day 5 exercise sweat urea N excretion were measured. Serum urea N and creatinine increased significantly during the treadmill run under both dietary conditions (P less than 0.05). No significances between diet differences were observed in sweat or urinary urea N excretion; however, excretion of both tended to be higher on the REC-PRO diet than on the HI-PRO diet. The differences in protein intake combined with the nitrogen excretion measures resulted in significant differences in estimated whole-body nitrogen retention between the two treatments. Nitrogen retention (means +/- SE) remained positive during the HI-PRO trial (2.41 +/- 1.99 g/day) but was significantly (P less than 0.005) reduced to -5.29 +/- 2.58 g/day during the REC-PRO trial. These results suggest that the current protein RDA may be inadequate for athletes engaging in chronic high-intensity endurance exercise. Future studies are needed to confirm this observation.

Adult↗
PubMed1989

Urea production during prolonged swimming.

Male interscholastic swimmers (n = 8) completed a 4572 m training swim in in 62 +/- 1.1 min (means +/- S.E.) with terminal heart rate and blood lactate of 152 +/- 6 beats min-1 and 6.9 +/- 0.89 mM, respectively. Sweat rate (0.48 +/- 0.095 l. h-1) was lower than similar intensity cycling (1.5 +/- 0.13 l. h-1) or running (1.1 +/- 0.14 l. h-1). Post-swim serum urea N (11.6 +/- 0.71 mM) was elevated (P less than 0.05) vs pre-swim (4.6 +/- 0.39 mM). Post-swim urine volume (860 +/- 75 ml 24 h-1) was reduced (P less than 0.07) and resulted in an elevated (P less than 0.05), but delayed (24-84 h), post-exercise urea N excretion. Although the reduced urine and sweat production during the swim undoubtedly contributed to the elevated serum urea, there must be another explanation because together they could only account for 38% of the observed increase. On the basis of the magnitude of serum urea increase, it appears that the swim caused an increase in urea production (amino acid oxidation). The failure to observe larger increases in urinary urea during recovery indicates that either urea excretion following exercise continues for prolonged periods of time (greater than 48 h) or another significant mode of nitrogen excretion exists.

Adolescent↗
PubMed1988

Effect of ambient temperature on protein breakdown during prolonged exercise.

Male subjects (n = 8) cycled for 90 min in 5, 20, and 30 degrees C environments. Rectal (Tre), chest, and thigh temperatures, O2 consumption (VO2), respiratory exchange ratio (R), and venous concentrations of glucose, free fatty acids (FFA), urea N, lactic acid (LA), norepinephrine (NE), epinephrine (E), and cortisol (C) were measured before, during, and after exercise. Urea N excretion was measured in 72 h of nonexercise, in 72 h of exercise (exercise day + 2 post-exercise days) urine samples, and in exercise sweat. Calculated 72-h protein utilization (means +/- SE) was significantly greater (P less than 0.05) for the 5 (86.9 +/- 27.1 g) and 20 (82.9 +/- 22.7 g) compared with 30 degrees C (34.01 +/- 19.1 g) trial. Regardless of ambient temperature exercise increased the venous concentration of C, E, and NE. These catabolic hormones were greatest in 5, lowest in 20, and intermediate in 30 degrees C. Exercise Tre and VO2 were greatest in the 30 degrees C environment. Venous FFA concentration was significantly higher and R significantly lower in 5 vs. 20 or 30 degrees C, and venous LA concentration was significantly greater in 30 vs. 20 or 5 degrees C. Although these results indicate that exercise protein breakdown is affected by ambient temperatures, the mechanism of action is not due solely to circulating NE, E, and C. Differences in venous FFA and LA across environmental temperatures suggest that alterations in carbohydrate and fat metabolism may have contributed to the observed variable protein utilization.

Adult↗
PubMed1987

Protein and exercise: update 1987.

Currently, the recommended dietary allowance for protein determined for sedentary individuals is assumed to be adequate for athletes. However, several types of evidence (in vitro, in situ, and in vivo) indicate that exercise causes substantial changes in protein metabolism. In fact, recent data suggest the protein recommended dietary allowance may actually be 50 to 100% higher for individuals who exercise on a regular basis. Optimal intakes, although unknown, may even be higher, especially for individuals attempting to increase muscle mass and strength. The reasons why the recent experimental results contradict older studies are complex and not fully understood. However, dietary (total energy input, percent of each foodstuff, accommodation to treatments), exercise (type, frequency, intensity, duration, training, environment), and methodological (in vitro, in situ, in vivo) considerations are likely very important. This paper reviews the recent findings and discusses their implications to exercise performance. Although, definitive recommendations regarding optimal protein intakes for various athletic groups are not yet possible, it appears that exercise increases protein needs. It is hoped that well-controlled studies will be completed in the near future so that such recommendations will soon be possible.

Dietary Proteins↗
PubMed1987

Menstrual cycle and exercise effects on protein catabolism.

The purpose of this investigation was to determine whether exercise at different times of the menstrual cycle alters protein catabolism. Nine women exercised for 60 min at 70% VO2max when serum estradiol (E) and progesterone (P) were low (menses) and when both were high [mid-luteal (ML)]. Diet was reproduced on both occasions. Serum urea nitrogen (N), E, and P were analyzed at rest, after 15, 30, 45, and 60 min of exercise, and 15 min into recovery. Sweat urea N excretion was also determined. Urinary area N excretion was measured the day before, the day of, and 2 d following exercise. E and P were significantly greater in the ML phase, and this difference was maintained throughout exercise (P less than 0.05). No change was seen in serum urea N across exercise or between phases. Both exercise day urinary urea N excretion and total urea N excretion in sweat and urine, when added across all experimental days, were significantly greater in the ML phase compared to menses (8.5 +/- 0.96 vs 5.5 +/- 0.81 g and 24.8 +/- 2.38 vs 19.3 +/- 1.38 g, respectively, P less than 0.05). The data suggest that the greater protein use in the ML phase was due to the combined effects of exercise, a changing hormonal milieu and other unknown causes.

Adult↗
PubMed1986

Validity/reliability of sweat analysis by whole-body washdown vs. regional collections.

Six subjects (25.3 +/- 3.3 yr, mean +/- SD) exercised for 60 min at 42 +/- 4 [low (L)], 55 +/- 6 [moderate (M)], and 67 +/- 4 %VO2max [high (H)] in a moderate environment. Sweat collected from upper back (UB), lower back (LB), midchest (MC), stomach (S), and thigh (T) areas as well as by whole-body washdown (W) was analyzed for urea nitrogen (N). With the exception of the L where all regional measures were similar, all sites overestimated W (several significantly, P less than 0.05). Regression analysis estimations of W (mg/h) from regional collections were as follows--L: W = 0.727 (S) - 1.366(UB) + 1.181(T) + 65.470 +/- 29.5, R = 0.90; M: W = 0.598(MC) - 0.649(UB) + 0.244(LB) + 43.238 +/- 30.4, R = 0.99; H: W = 0.274(S) - 0.560(T) + 0.223(MC) + 131.104 +/- 4.3, R = 0.99; All Intensities: W = 0.497(MC) - 0.483(T) + 0.112(LB) + 69.554 +/- 31.5, R = 0.96. W recovery of exogenous urea N applied to each subject's body was 98.3 +/- 2.7% (mean +/- SE). Interinvestigator reliability coefficient (r = 0.511) was significant (P less than 0.01) but relatively low and the between investigator urea N recovery (93.3 +/- 3.7 vs. 103.2 +/- 3.5%) was significantly different (P less than 0.05). Repeated W determinations by the same investigator were not different (P greater than 0.05), but intrainvestigator reliability coefficients differed widely (0.385 vs. 0.820). Together, these data indicate that W solute recovery can be high; however, both inter- and intrainvestigator reliability can vary.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Effect of daily exercise and food intake on leucine oxidation.

Oxidation of the branched-chain amino acid leucine was studied in 22 male Sprague-Dawley rats (70-90 g) over 3 days following the ingestion on Day 1 of a mixed diet containing a tracer dose (10 muCi) of L-[1-14C]Leu. One group (E) completed 1 hr exercise at 80% VO2 max immediately after a 2-hr feeding period on all 3 days, while a second group served as a control. Rats from group E were sacrificed immediately after the 2 hr feeding on Day 1, following exercise on Days 1 and 3, and at the end of Day 3. The following were determined: (1) continuous 14CO2 production, (2) radioactivity remaining in the gastrointestinal tract, and (3) distribution of free vs protein bound 14C in muscle and liver. The results indicated that (1) 14CO2 production increased during exercise on all 3 days (P less than 0.01), (2) 14CO2 production also increased (P less than 0.05) following food intake (unlabeled diet), (3) 14CO2 production due to exercise was greater than that due to food intake (P less than 0.05), (4) absolute 14CO2 production decreased dramatically by 15 hr of Day 1 (P less than 0.01) with little change thereafter (except with exercise and food intake on Days 2 and 3), (5) greater than 98% of the labeled diet was absorbed from the GIT 51 hr postingestion, and (6) 14C in the free pool of muscle and liver could account for less than 15% of the total 14CO2 production. These results suggest that protein bound 14C in addition to free 14C may be responsible for a significant proportion of the observed increased 14CO2 production during exercise.

Animals↗
PubMed1985

Feasibility of sweat collection by whole body washdown in moderate to high humidity environments.

When sweat rates are sufficiently elevated, i.e., in high ambient temperatures or during exercise, due to potential losses of sweat by runoff, the whole body washdown technique of sweat collection is considered invalid in all but low humidity environments. This paper describes a modification of this technique that makes its use possible in moderate to high humidity environments. During exercise, sweat loss by runoff was minimized by maximizing evaporation of sweat (subjects wore little clothing and electric fans were utilized) and by drying the surface of the body when sweat became excessive (with small hand towels). Sweat rate was calculated from weight changes with appropriate corrections. Total sweat content and concentration of urea N were determined from the rinsings of the body, hand towels, and clothing. To validate this procedure, runoff sweat that was not collected was estimated from the weight change of collecting towels positioned under a bicycle ergometer. Eight subjects exercised at approximately 60% VO2max for 30 min in 22.6 degrees +/- 0.46 degrees C (means +/- SD) and 66.1% +/- 2.34% RH. Volume of sweat secreted was 581 +/- 31 ml (1.162 +/- .062 l X h-1; means +/- SE). Sweat content of the collecting towels (corrected for evaporation loss) was 4.675 ml (0.8%) of total sweat rate), indicating that it is possible to prevent significant sweat loss with this procedure. Moreover, we have found that this procedure can be employed with little difficulty at exercise intensities up to approximately 75% VO2max, in RH of approximately 70%, and with sweat rates as high as 1.65 l X h-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise Test↗
PubMed1982

In vivo leucine oxidation at rest and during two intensities of exercise.

After ingestion of a mixed diet containing a tracer dose (10 muCi) of L-[1-14C]leucine (Leu), 32 male Sprague-Dawley rats (70-90 g) remained at rest (R) or completed 1 h exercise at 80 (E80) or 40% VO2max (E40). 14CO2 production was assessed for 6 h (exercise occurred from h 2 to 3). Four rats were killed at 2, 3, 4, and 6 h (R), at 3 and 6 h (E80), and at 6 h (E40). Determinations were 1) tissue specific activity dpm X mumol-1 from a) mixed skeletal muscle (gastrocnemius, soleus, quadriceps, and hamstrings) and b) liver and 2) radioactivity remaining in the gastrointestinal tract (GIT). Leu oxidized (mumol) was estimated (14 CO2 dpm X tissue sp act dpm-1 X mumol-1) independently from skeletal muscle and liver. Results were 1) 14CO2 production increased in both E80 and E40 compared with R (P less than 0.05), 2) E80 14CO2 increase was greater than E40 (P less than 0.05), 3) GIT absorption was reduced in E80 and E40 compared with R (P less than 0.05), and 4) exercise Leu oxidation (weighted average of tissue estimates) was 26% greater than R (P less than 0.05). The origin and site of the increased Leu oxidation cannot be determined from the present data; however, due to the magnitude of increase in skeletal muscle metabolism relative to other tissues during exercise, it is probable that skeletal muscle plays a significant role.

Animals↗
PubMed1981

Effects of exercise on protein and amino acid metabolism.

At rest, especially during starvation, protein (via hepatic gluconeogenesis and/or direct oxidation) contributes significantly to the body's total metabolic requirement. During exercise, carbohydrate (CHO) and free fatty acids (FFA) are generally regarded as the major energy sources. Although protein has the capability, it has seldom been considered as an important exercise energy source based largely on 24-h urinary nitrogen (N) excretion values. Contrary to classical belief, recent determinations of N in sweat suggest that total N excretion is in fact increased with exercise. This should not be surprising when one considers that prolonged exercise substrate shifts and hormonal changes are in many ways analogous to the situation that occurs during starvation. In addition, in vitro experiments have demonstrated that skeletal muscle, as well as liver, has the capacity to oxidize a number of amino acids. This information, together with the in vivo exercise observations of an increased alanine output from skeletal muscle and an increased 14CO2 evolution following [14C] leucine injection or ingestion, indicates that some amino acids contribute to exercise energy needs. Although a number of mechanisms have been suggested, the current evidence strongly suggests that the branched-chain amino acids (glucose-alanine cycle) are the most important. In conclusion, it appears that the earlier studies which indicated that protein/amino acid utilization did not increase during exercise may have been premature. Although clearly not as important as either CHO or FFA, recent investigations employing both humans and laboratory animals suggest that protein/amino acids, under some conditions, may contribute significantly to total exercise calories.

Amino Acids↗
PubMed1980

Effect of initial muscle glycogen levels on protein catabolism during exercise.

Serum urea increases with exercise duration suggest prolonged exercise may be analogous to starvation where protein catabolism is known to occur. The purpose of this investigation was to alter muscle glycogen levels and to study the effect on protein catabolism. Six subjects (27-30 yr) pedaled a cycle ergometer for 1 h at 61% VO2max (mean VO2 = 2.33 +/- 0.7 1 . min-1) 1) after CHO loading (CHOL) and 2) after CHO depletion (CHOD). The following urea N measures were made: pre-exercise serum and urine, exercise serum and sweat (15-min serial samples), and serum and urine during 240 recovery min. Results demonstrated that 1) exercise serum urea N increased in CHOD attaining significance (P less than 0.01) at 60 min; 2) serum urea N increases continued into recovery at all measurement points of CHOD (P less than 0.01) and at 240 min of CHOL (P less than 0.05); 3) sweat urea N increased 154.2-fold (CHOD) and 65.6-fold (CHOL) (P less than 0.05). Calculations indicate that CHOD sweat urea N excretion was equivalent to a protein breakdown of 13.7 g . h-1 or 10.4% of the total caloric cost. It was concluded that protein is utilized during exercise to a greater extent than is generally assumed and that under certain conditions protein carbon may contribute significantly to exercise caloric cost.

Adult↗
PubMed1980

Exercise VO2 estimation using recovery sampling.

Various situations present a challenge to determine oxygen uptake (VO2) accurately simply because of the restrictions imposed by the equipment employed. This investigation was undertaken to 1) compare a select number of recovery VO2 measurements with respect to their accuracy in estimating actual exercise VO2 and 2) to determine whether absolute workload or VO2max affect this relationship. Fifteen subjects [8 highly trained (HT), VO2max +/- SD = 70.2 +/- 3.5 ml/kg . min-1 and 7 untrained (UT), VO2max = 49.7 +/- 3.8 ml/kg . min-1] completed a number of 5 min workbouts on a bicycle ergometer at 25-70% VO2max (VO2 = .899--3.879 l . min-1). VO2 and VCO2 (l . min-1) were monitored continuously throughout the exercise and for 5 min of recovery via a breath-by-breath system. The results indicated that 1) exercise VO2 +/- Sy.x can be estimated from several recovery collection periods, the first breath y = .953X + .441 +/- .319, the first two breaths y = 1.046X + .327 +/- .270, the first three breaths y = 1.089X + .260 +/- .241, and the second three breaths y = 1.101X + .387 +/- .234, and 2) VO2max does not affect this relationship (p greater than 0.05) while increasing absolute workload produces a greater exercise VO2 underestimation (p less than 0.05). It was concluded that using this method exercise VO2 can be estimated with reasonable accuracy (Sy.x = .234--.319, r = .92--.94, p less than 0.01).

Adult↗
PubMed1977

Physiological profile of professional fire fighters.

This investigation assessed the physical characteristics, functional capacities, and body composition of 45 professional fire fighters, aged 23 through 49 years. Maximum oxygen uptake (VO2), Recovery Oxygen Uptake, arm and leg strength, all showed a negative linear relationship with age. On the other hand, percent body fat increased with age from 18% to 21%. Hand grip strength did not decline significantly as the grip strength values remained fairly constant for all of the fire fighters. Most of the data collected were considered to be within the normal range of the sedentary North American population. It was concluded from these data that professional fire fighters might well benefit from a training program designed to develop and maintain a higher level of personal fitness.

Aerobiosis↗
PubMedDate not supplied

The importance of protein for athletes.

Although it is generally believed that carbohydrate and fat are the only sources of energy during physical activity, recent experimental results suggest that there are also significant alterations in protein metabolism during exercise. Depending on several factors, including intensity, duration and type of exercise, as well as prior diet, training, environment and perhaps even gender or age, these changes may be quite large. Generally, exercise promotes: a decrease in protein synthesis (production) unless the exercise duration is prolonged (greater than 4h) when increases occur; either an increase or no change in protein catabolism (breakdown); and an increase in amino acid oxidation. In addition, significant subcellular damage to skeletal muscle has been shown following exercise. Taken together, these observations suggest that the protein requirements of active individuals are greater than those of inactive individuals. Although the underlying reasons are different, this statement applies to both endurance and strength/power athletes. At present, it is not possible to precisely determine protein requirements. However, because deficiencies in total protein or in specific amino acids may occur, we suggest that athletes consume 1.8 to 2.0 g of protein/kg of bodyweight/day. This is approximately twice the recommended requirement for sedentary individuals. For some athletes this may require supplementation; however, these quantities of protein can be easily obtained in a diet where 12 to 15% of the total energy is from protein. Although the effect of exercise on protein metabolism has been studied for many years, numerous questions remain. Hopefully, with the recent renewed interest in this area of study, most of these answers will soon be available.

Dietary Proteins↗