Heat stress increases muscle glycogen use but reduces the oxidation of ingested carbohydrates during exercise

2002 ◽  
Vol 92 (4) ◽  
pp. 1562-1572 ◽  
Author(s):  
Roy L. P. G. Jentjens ◽  
Anton J. M. Wagenmakers ◽  
Asker E. Jeukendrup
Keyword(s):  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Oxidation Rate ◽  
Glucose Oxidation ◽  
Statistical Significance ◽  
Maximal Oxygen Consumption ◽  
Exogenous Glucose ◽  
Cool Environment ◽  
Lower Plasma Glucose ◽  
Glucose Plasma

The aim of the present study was to test the hypothesis that the oxidation rate of ingested carbohydrate (CHO) is impaired during exercise in the heat compared with a cool environment. Nine trained cyclists (maximal oxygen consumption 65 ± 1 ml · kg body wt−1 · min−1) exercised on two different occasions for 90 min at 55% maximum power ouptput at an ambient temperature of either 16.4 ± 0.2°C (cool trial) or 35.4 ± 0.1°C (heat trial). Subjects received 8% glucose solutions that were enriched with [U-13C]glucose for measurements of exogenous glucose, plasma glucose, liver-derived glucose and muscle glycogen oxidation. Exogenous glucose oxidation during the final 30 min of exercise was significantly ( P < 0.05) lower in the heat compared with the cool trial (0.76 ± 0.06 vs. 0.84 ± 0.05 g/min). Muscle glycogen oxidation during the final 30 min of exercise was increased by 25% in the heat (2.07 ± 0.16 vs. 1.66 ± 0.09 g/min; P < 0.05), and liver-derived glucose oxidation was not different. There was a trend toward a higher total CHO oxidation and a lower plasma glucose oxidation in the heat although this did not reach statistical significance ( P = 0.087 and P = 0.082, respectively). These results demonstrate that the oxidation rate of ingested CHO is reduced and muscle glycogen utilization is increased during exercise in the heat compared with a cool environment.

scholarly journals Oral [13C]glucose oxidation during prolonged exercise after high- and low-carbohydrate diets

1998 ◽  
Vol 85 (2) ◽  
pp. 723-730 ◽  
Author(s):  
F. Péronnet ◽  
N. Rhéaume ◽  
C. Lavoie ◽  
C. Hillaire-Marcel ◽  
D. Massicotte
Keyword(s):  
Oxygen Uptake ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Maximal Oxygen Uptake ◽  
Oxidation Rate ◽  
Glucose Oxidation ◽  
Prolonged Exercise ◽  
Exogenous Glucose ◽  
Low Carbohydrate ◽  
The Difference

The effect of a diet either high or low in carbohydrates (CHO) on exogenous 13C-labeled glucose oxidation (200 g) during exercise (ergocycle: 120 min at 64.0 ± 0.5% maximal oxygen uptake) was studied in six subjects. Between 40 and 80 min, exogenous glucose oxidation was significantly higher after the diet low in CHO (0.63 ± 0.05 vs. 0.52 ± 0.04 g/min), but this difference disappeared between 80 and 120 min (0.71 ± 0.03 vs. 0.69 ± 0.04 g/min). The oxidation rate of plasma glucose, computed from the volume of13CO2produced the13C-to-12C ratio in plasma glucose at 80 min, and of glucose released from the liver, computed from the difference between plasma glucose and exogenous glucose oxidation, was higher after the diet low in CHO (1.68 ± 0.26 vs. 1.41 ± 0.17 and 1.02 ± 0.20 vs. 0.81 ± 0.14 g/min, respectively). In contrast the oxidation rate of glucose plus lactate from muscle glycogen (computed from the difference between total CHO oxidation and plasma glucose oxidation) was lower (0.31 ± 0.35 vs. 1.59 ± 0.20 g/min). After a diet low in CHO, the oxidation of exogenous glucose and of glucose released from the liver is increased and partly compensates for the reduction in muscle glycogen availability and oxidation.

Oxidation of an oral [13C]glucose load at rest and prolonged exercise in trained and sedentary subjects

1999 ◽  
Vol 86 (1) ◽  
pp. 52-60 ◽  
Author(s):  
Y. Burelle ◽  
F. Péronnet ◽  
S. Charpentier ◽  
C. Lavoie ◽  
C. Hillaire-Marcel ◽  
...  
Keyword(s):  
Oxygen Uptake ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Glucose Oxidation ◽  
Prolonged Exercise ◽  
Glucose Load ◽  
Exogenous Glucose ◽  
Glycogen Stores ◽  
Male Subjects ◽  
Sedentary Subjects

The purpose of this study was to compare the oxidation of [13C]glucose (100 g) ingested at rest or during exercise in six trained (TS) and six sedentary (SS) male subjects. The oxidation of plasma glucose was also computed from the volume of13CO2and13C/12C in plasma glucose to compute the oxidation rate of glucose released from the liver and from glycogen stores in periphery (mainly muscle glycogen stores during exercise). At rest, oxidative disposal of both exogenous (8.3 ± 0.3 vs. 6.6 ± 0.8 g/h) and liver glucose (4.4 ± 0.5 vs. 2.6 ± 0.4 g/h) was higher in TS than in SS. This could contribute to the better glucose tolerance observed at rest in TS. During exercise, for the same absolute workload [140 ± 5 W: TS = 47 ± 2.5; SS = 68 ± 3 %maximal oxygen uptake (V˙o 2 max)], [13C]glucose oxidation was higher in TS than in SS (39.0 ± 2.6 vs. 33.6 ± 1.2 g/h), whereas both liver glucose (16.8 ± 2.4 vs. 24.0 ± 1.8 g/h) and muscle glycogen oxidation (36.0 ± 3.0 vs. 51.0 ± 5.4 g/h) were lower. For the same relative workload (68 ± 3% V˙o 2 max: TS = 3.13 ± 0.96; SS = 2.34 ± 0.60 l O2/min), exogenous glucose (44.4 ± 1.8 vs. 33.6 ± 1.2 g/h) and muscle glycogen oxidation (73.8 ± 7.2 vs. 51.0 ± 5.4 g/h) were higher in TS. However, despite a higher energy expenditure in TS, liver glucose oxidation was similar in both groups (22.2 ± 3.0 vs. 24.0 ± 1.8 g/h). Thus exogenous glucose oxidation was selectively favored in TS during exercise, reducing both liver glucose and muscle glycogen oxidation.

scholarly journals Substrate source utilization during moderate intensity exercise with glucose ingestion in Type 1 diabetic patients

2007 ◽  
Vol 103 (1) ◽  
pp. 119-124 ◽  
Author(s):  
M. Robitaille ◽  
M.-C. Dubé ◽  
S. J. Weisnagel ◽  
D. Prud'homme ◽  
D. Massicotte ◽  
...  
Keyword(s):  
Oxygen Uptake ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Maximal Oxygen Uptake ◽  
Glucose Oxidation ◽  
Substrate Oxidation ◽  
Moderate Intensity ◽  
Diabetic Patients ◽  
Control Subjects ◽  
Exogenous Glucose

Substrate oxidation and the respective contributions of exogenous glucose, glucose released from the liver, and muscle glycogen oxidation were measured by indirect respiratory calorimetry combined with tracer technique in eight control subjects and eight diabetic patients (5 men and 3 women in both groups) of similar age, height, body mass, and maximal oxygen uptake, over a 60-min exercise period on cycle ergometer at 50.8% (SD 4.0) maximal oxygen uptake [131.0 W (SD 38.2)]. The subjects and patients ingested a breakfast (containing ∼80 g of carbohydrates) 3 h before and 30 g of glucose (labeled with 13C) 15 min before the beginning of exercise. The diabetic patients also received their usual insulin dose [Humalog = 9.1 U (SD 0.9); Humulin N = 13.9 U (SD 4.4)] immediately before the breakfast. Over the last 30 min of exercise, the oxidation of carbohydrate [1.32 g/min (SD 0.48) and 1.42 g/min (SD 0.63)] and fat [0.33 g/min (SD 0.10) and 0.30 g/min (SD 0.10)] and their contribution to the energy yield were not significantly different in the control subjects and diabetic patients. Exogenous glucose oxidation was also not significantly different in the control subjects and diabetic patients [6.3 g/30 min (SD 1.3) and 5.2 g/30 min (SD 1.6), respectively]. In contrast, the oxidation of plasma glucose and oxidation of glucose released from the liver were significantly lower in the diabetic patients than in control subjects [14.5 g/30 min (SD 4.3) and 9.3 g/30 min (SD 2.8) vs. 27.9 g/30 min (SD 13.3) and 21.6 g/30 min (SD 12.8), respectively], whereas that of muscle glycogen was significantly higher [28.1 g/30 min (SD 15.5) vs. 11.6 g/30 min (SD 8.1)]. These data indicate that, compared with control subjects, in diabetic patients fed glucose before exercise, substrate oxidation and exogenous glucose oxidation overall are similar but plasma glucose oxidation is lower; this is associated with a compensatory higher utilization of muscle glycogen.

Respective oxidation of13C-labeled lactate and glucose ingested simultaneously during exercise

1997 ◽  
Vol 82 (2) ◽  
pp. 440-446 ◽  
Author(s):  
F. Péronnet ◽  
Y. Burelle ◽  
D. Massicotte ◽  
C. Lavoie ◽  
C. Hillaire-Marcel
Keyword(s):  
Oxygen Uptake ◽  
Plasma Glucose ◽  
Oxidation Rate ◽  
Prolonged Exercise ◽  
The Other ◽  
Energy Yield ◽  
Exogenous Glucose ◽  
Gastrointestinal Discomfort ◽  
Cumulative Amount ◽  
Male Subjects

Péronnet, F., Y. Burelle, D. Massicotte, C. Lavoie, and C. Hillaire-Marcel. Respective oxidation of13C-labeled lactate and glucose ingested simultaneously during exercise. J. Appl. Physiol. 82(2): 440–446, 1997.—The purpose of this experiment was to measure, by using13C labeling, the oxidation rate of exogenous lactate (25 g, as Na+, K+, Ca2+, and Mg2+ salts) and glucose (75 g) ingested simultaneously (in 1,000 ml of water) during prolonged exercise (120 min, 65 ± 3% maximum oxygen uptake in 6 male subjects). The percentage of exogenous glucose and lactate oxidized were similar (48 ± 3 vs. 45 ± 5%, respectively). However, because of the small amount of oral lactate that could be tolerated without gastrointestinal discomfort, the amount of exogenous lactate oxidized was much smaller than that of exogenous glucose (11.1 ± 0.5 vs. 36.3 ± 1.3 g, respectively) and contributed to only 2.6 ± 0.4% of the energy yield (vs. 8.4 ± 1.9% for exogenous glucose). The cumulative amount of exogenous glucose and lactate oxidized was similar to that observed when 100 g of [13C]glucose were ingested (47.3 ± 1.8 vs. 50.9 ± 1.2 g, respectively). When [13C]glucose was ingested, changes in the plasma glucose13C/12C ratio indicated that between 39 and 61% of plasma glucose derived from exogenous glucose. On the other hand, the plasma glucose13C/12C ratio remained unchanged when [13C]lactate was ingested, suggesting no prior conversion into glucose before oxidation.

Oral [13C]glucose and endogenous energy substrate oxidation during prolonged treadmill running

2002 ◽  
Vol 92 (3) ◽  
pp. 1255-1260 ◽  
Author(s):  
Stéphane Couture ◽  
Denis Massicotte ◽  
Carole Lavoie ◽  
Claude Hillaire-Marcel ◽  
François Péronnet
Keyword(s):  
Plasma Glucose ◽  
Oxidation Rate ◽  
Glucose Oxidation ◽  
Substrate Oxidation ◽  
Treadmill Running ◽  
Energy Substrate ◽  
Running Exercise ◽  
Sweat Production ◽  
Glucose Ingestion ◽  
Endogenous Glucose

Six male subjects were studied during running exercise (120 min, 69% maximal oxygen consumption) with ingestion of a placebo or 3.5 g/kg of [13C]glucose (∼2 g/min). Indirect respiratory calorimetry corrected for urea excretion in urine and sweat, production of 13CO2 at the mouth, and changes in plasma glucose 13C/12C were used to compute energy substrate oxidation. The oxidation rate of exogenous glucose increased from 1.02 at minute 60 to 1.22 g/min at minute 120 providing ∼24 and 33% of the energy yield (%En). Glucose ingestion did not modify protein oxidation, which provided ∼4–5%En, but significantly increased glucose oxidation by ∼7%, reduced lipid oxidation by ∼16%, and markedly reduced endogenous glucose oxidation (1.25 vs. 2.21 g/min between minutes 80 and 120, respectively). The oxidation rate of glucose released from the liver (0.38 and 0.47 g/min, or 10–13%En at minutes 60 and 120, respectively), and of plasma glucose (1.30–1.69 g/min, or 34 and 45%En and 50 and 75% of glucose oxidation) significantly increased from minutes 60 to 120, whereas the oxidation of muscle glycogen significantly decreased (1.28 to 0.58 g of glucose/min, or 34 and 16%En and 50 and 25% of glucose oxidation). These results indicate that, during moderate prolonged running exercise, ingestion of a very large amount of glucose significantly reduces endogenous glucose oxidation, thus sparing muscle and/or liver glycogen stores.

Effect of cold exposure on fuel utilization in humans: plasma glucose, muscle glycogen, and lipids

2002 ◽  
Vol 93 (1) ◽  
pp. 77-84 ◽  
Author(s):  
François Haman ◽  
François Péronnet ◽  
Glen P. Kenny ◽  
Denis Massicotte ◽  
Carole Lavoie ◽  
...  
Keyword(s):  
Heat Production ◽  
Cold Exposure ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Glucose Oxidation ◽  
Future Research ◽  
Oxidation Rates ◽  
Low Intensity ◽  
Glucose Ingestion ◽  
Shivering Thermogenesis

The relative roles of circulatory glucose, muscle glycogen, and lipids in shivering thermogenesis are unclear. Using a combination of indirect calorimetry and stable isotope methodology ([U-13C]glucose ingestion), we have quantified the oxidation rates of these substrates in men acutely exposed to cold for 2 h (liquid conditioned suit perfused with 10°C water). Cold exposure stimulated heat production by 2.6-fold and increased the oxidation of plasma glucose from 39.4 ± 2.4 to 93.9 ± 5.5 mg/min (+138%), of muscle glycogen from 126.6 ± 7.8 to 264.2 ± 36.9 mg glucosyl units/min (+109%), and of lipids from 46.9 ± 3.2 to 176.5 ± 17.3 mg/min (+376%). Despite the observed increase in plasma glucose oxidation, this fuel only supplied 10% of the energy for heat generation. The major source of carbohydrate was muscle glycogen (75% of all glucose oxidized), and lipids produced as much heat as all other fuels combined. During prolonged, low-intensity shivering, we conclude that total heat production is unequally shared among lipids (50%), muscle glycogen (30%), plasma glucose (10%), and proteins (10%). Therefore, future research should focus on lipids and muscle glycogen that provide most of the energy for heat production.

Effect of carbohydrate ingestion on metabolism during running and cycling

2001 ◽  
Vol 91 (5) ◽  
pp. 2125-2134 ◽  
Author(s):  
Melissa J. Arkinstall ◽  
Clinton R. Bruce ◽  
Vasilis Nikolopoulos ◽  
Andrew P. Garnham ◽  
John A. Hawley
Keyword(s):  
Body Mass ◽  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Lactate Threshold ◽  
Glucose Oxidation ◽  
Dry Mass ◽  
Carbohydrate Oxidation ◽  
Total Carbohydrate ◽  
Carbohydrate Ingestion ◽  
Glycogen Utilization

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-14C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 ± 20 vs. 42 ± 16 g/h; P < 0.01) and cycling (57 ± 16 vs. 35 ± 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 ± 4 vs. 23 ± 3%; P < 0.01) and cycling (36 ± 5 vs. 22 ± 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 ± 32 vs. 141 ± 34 mmol/kg dry mass) or cycling (227 ± 36 vs. 216 ± 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.

Muscle glycogen oxidation during prolonged exercise measured with oral [13C]glucose: comparison with changes in muscle glycogen content

2007 ◽  
Vol 102 (5) ◽  
pp. 1773-1779 ◽  
Author(s):  
C. R. Harvey ◽  
R. Frew ◽  
D. Massicotte ◽  
F. Péronnet ◽  
N. J. Rehrer
Keyword(s):  
Plasma Glucose ◽  
Muscle Glycogen ◽  
Glucose Oxidation ◽  
Prolonged Exercise ◽  
Vastus Lateralis ◽  
Energy Yield ◽  
Vastus Lateralis Muscle ◽  
Tracer Technique ◽  
Total Carbohydrate ◽  
Tracer Techniques

Plasma glucose and muscle glycogen oxidation during prolonged exercise [75-min at 48 and 76% maximal O2 uptake (V̇o2 max)] were measured in eight well-trained male subjects [V̇o2 max = 4.50 l/min (SD 0.63)] using a simplified tracer technique in which a small amount of glucose highly enriched in 13C was ingested: plasma glucose oxidation was computed from 13C/12C in plasma glucose (which was stable beginning at minute 30 and minute 15 during exercise at 48 and 76% V̇o2 max, respectively) and 13CO2 production, and muscle glycogen oxidation was estimated by subtracting plasma glucose oxidation from total carbohydrate oxidation. Consistent data from the literature suggest that this small dose of exogenous glucose does not modify muscle glycogen oxidation and has little effect, if any, on plasma glucose oxidation. The percent contributions of plasma glucose and muscle glycogen oxidation to the energy yield at 48% V̇o2 max [15.1% (SD 3.8) and 45.9% (SD 5.8)] and at 76% V̇o2 max [15.4% (SD 3.6) and 59.8% (SD 9.2)] were well in line with data previously reported for similar work loads and exercise durations using conventional tracer techniques. The significant reduction in glycogen concentration measured from pre- and postexercise vastus lateralis muscle biopsies paralleled muscle glycogen oxidation calculated using the tracer technique and was larger at 76% than at 48% V̇o2 max. However, the correlation coefficients between these two estimates of muscle glycogen utilization were not different from zero at each of the two work loads. The simplified tracer technique used in the present experiment appears to be a valid alternative approach to the traditional tracer techniques for computing plasma glucose and muscle glycogen oxidation during prolonged exercise.

scholarly journals Effects of carbohydrate availability on sustained shivering I. Oxidation of plasma glucose, muscle glycogen, and proteins

2004 ◽  
Vol 96 (1) ◽  
pp. 32-40 ◽  
Author(s):  
François Haman ◽  
François Péronnet ◽  
Glen P. Kenny ◽  
Éric Doucet ◽  
Denis Massicotte ◽  
...  
Keyword(s):  
Heat Production ◽  
Plasma Glucose ◽  
Indirect Calorimetry ◽  
Muscle Glycogen ◽  
Glucose Oxidation ◽  
Fuel Selection ◽  
Glucose Ingestion ◽  
Diet And Exercise ◽  
Tracer Methods ◽  
A Minor

Carbohydrates (CHO) can play an important thermogenic role during shivering, but the effect of their availability on the use of other oxidative fuels is unclear. Using indirect calorimetry and tracer methods ([U-13C]glucose ingestion), we have determined the specific contributions of plasma glucose, muscle glycogen, proteins, and lipids to total heat production (Ḣprod) in men exposed to cold for 2-h (liquid-conditioned suit perfused with 10°C water). Measurements were made after low-CHO diet and exercise (Lo) and high-CHO diet without exercise (Hi). The size of CHO reserves had no effect on Ḣprod but a major impact on fuel selection before and during shivering. In the cold, a complete shift from lipid oxidation for Lo (53, 28, and 19% Ḣprod for lipids, CHO, and proteins, respectively) to CHO-based metabolism for Hi (23, 65, and 12% Ḣprod for lipids, CHO, and proteins, respectively) was observed. Plasma glucose oxidation remains a minor fuel under all conditions (<13% Ḣprod), falling to 7% Ḣprod for Lo. Therefore, adjusting plasma glucose oxidation to compensate for changes in muscle glycogen oxidation is not a strategy used for maintaining heat production. Instead, proteins and lipids share responsibility for this compensation. We conclude that humans can show remarkable flexibility in oxidative fuel selection to ensure that heat production is not compromised during sustained cold exposure.

scholarly journals Adolescent Pitcher Fatigue: Ulnar Collateral Ligament Stress, Flexor-Pronator Mass Energy Depletion, and Correlation to Pitch Count

2021 ◽  
Vol 9 (7_suppl4) ◽  
pp. 2325967121S0024
Author(s):  
Manuel Schubert ◽  
Tariq Awan ◽  
Aaron Sciascia ◽  
Emily Pacheco ◽  
Jennifer DeMink ◽  
...  
Keyword(s):  
Grip Strength ◽  
Muscle Glycogen ◽  
Repeated Measures ◽  
Statistical Significance ◽  
Ulnar Collateral Ligament ◽  
Glycogen Storage ◽  
Collateral Ligament ◽  
Time Points ◽  
Subjective Fatigue ◽  
Forearm Flexor

Objectives: There has been a rise in elbow ulnar collateral ligament (UCL) injuries in youth pitchers over recent years. With forearm flexor-pronator mass fatigue, the dynamic stability provided could be diminished placing greater stress on the UCL. Pitch count limits have been instituted in an attempt to help curtail this rise in throwing injuries, especially in youth athletes. In order to provide more objective data regarding current pitch count limits for youth pitchers, the purpose of this pilot study was to evaluate for potential fatigue of the flexor-pronator mass by assessing changes in medial elbow laxity, noninvasively characterizing changes in muscle glycogen storage within the forearm flexor-pronator mass, and evaluating changes in subjective fatigue, strength, range of motion (ROM), pitching velocity, and accuracy with increasing number of pitches thrown by 10-year-old pitchers up to their recommended 75 pitch count limit. Methods: After appropriate power analysis, male pitchers 10 years of age were recruited for the study (n=22). Pitchers threw a total of 75 pitches divided into sets of 25 pitches, with standardized periods of rest in between throws and sets to best simulate a game. Bilateral medial elbow laxity was measured by applying 10 decanewtons of valgus force with a standardized stress device and utilizing ultrasound imaging (Figures 1A-B) prior to pitching and after each pitching set. The change in medial ulnohumeral joint distance (Figure 1C) after stress was applied was calculated from baseline without stress. Relative changes in muscle glycogen storage, detected as changes in echogenicity, within the flexor carpi radialis (FCR) and the flexor digitorum superficialis (FDS)/flexor carpi ulnaris (FCU) muscles were measured non-invasively with ultrasound-based software (Figures 1D-E) and recorded as fuel percentile. Repeated measures analysis of variance and post-hoc testing were used to determine statistical significance (alpha=0.05). Results: There were no significant differences in medial elbow laxity between arms or time points. There was a trend for similar decline in FCR fuel percentile values between each arm, indicating relative decreases in glycogen storage bilaterally. However, only the throwing arm demonstrated a statistically significant decline in fuel percentile from baseline to after 75 pitches (p=0.05). There were no statistically significant differences across time points for FDS/FCU fuel percentile values. Fatigue measurements for both arms were significantly higher at all time points compared to baseline (p≤0.03). Grip strength of the dominant arm after 75 pitches was significantly decreased compared to after 25 pitches (p=0.02). There were no statistically significant changes in other strength measurements, ROM, velocity, or accuracy between all time points. Conclusions: By the recommended 75 pitch count limit in 10-year-olds, subjective fatigue and a decrease in grip strength had occurred. Furthermore, relative glycogen storage of the flexor-pronator mass of the throwing arm decreased between pitching 50 to 75 pitches, but without an increase in medial elbow gapping. This study provides a foundation and raises questions for further objective testing of physiologic changes that occur throughout increasing pitching to better guide pitch count limits and ensure the safety of young athletes

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