1 Metabolic Response to Exercise Foss ch. 3 Brooks - Exercise Phys. Ch. 10 –selected sections - Brooks Ch. 5-7 Outline Fuel utilization - crossover concept Recovery –Glycogen re-synthesis –lactate –performance Lactate shuttles Endurance Training effects –lactate, Glycolysis, mitochondria Anaerobic Threshold??

2 Measurement of Metabolic Response Evaluation provides info about absolute and relative intensity of exercise bout (fig 10.1a) –absolute VO 2 (L/min or ml/Kg/min) –% of VO 2 max –% of HR max –multiples of Metabolic Rate (MET’s) 1kcal/Kg/hour at rest; 3.5mlO 2 /kg/min determination of metabolic response allows estimation of –Total energy cost –Nutritional requirements –Efficiency calculations –Estimation of workload indicates metabolic system utilization, and the potential for fatigue

3 Substrate Utilization Brooks p 133 Power output is the most important factor determining fuel utilization Crossover concept –post absorptive and resting lipid used predominantly –with increasing intensity fuel mix switches from lipid to CHO Fig 7-12 training - displaces absolute intensity at which crossover occurs –epinephrine suppression –inc lactate clearance –inc mitochondria –prolong onset of glycogen breakdown, depletion and fatigue Fig 7-10

4 Fuel Utilization Fig 7-11 Glucose - fatty acid cycle FFA breakdown inhibits glycolysis PDH is inhibited by Acetyl-CoA from Beta oxidation PFK is inhibited by inc citrate from Beta oxidation and ATP –in highly trained and glycogen depleted this is accentuated –Fig higher FFA utilization with higher mitochondrial enzyme activity following training Hexokinase is inhibited by its product G6P, which builds up if glycolysis is not active.

5 Recovery from Exercise Ch. 3 - Foss process of recovery from exercise involves transition from catabolic to anabolic state –breakdown of glycogen and fats to replenishment of stores –breakdown of protein to protein synthesis for muscle growth and repair Our discussion of recovery will include; –oxygen consumption post exercise –Replenishment of energy stores –Lactate metabolism (energy or glycogen) –Replenishment of oxygen stores –intensity and activity specific recovery –guidelines for recovery

6 Recovery Oxygen Recovery O 2 - Net amount of oxygen consumed during recovery from exercise –excess above rest in Litres of O 2 Fast and Slow components –Based on slope of O 2 curve –first 2-3 min of recovery - O 2 consumption declines fast –then declines slowly to resting Fig 3.1 Fast Component - first 2-3 minutes –restore myoglobin and blood oxygen –energy cost of elevated ventilation –energy cost of elevate heart activity –replenishment of phosphagen volume of O 2 for fast component = area under curve – related to intensity not duration

7 Recovery Oxygen Slow Component –elevated body temperature Q10 effect - inc metabolic activity –cost of ventilation and heart activity –ion redistribution Na+/K+ pump –glycogen re-synthesis –effect of catecholamines and thyroid hormone –oxidation of lactate serves as fuel for many of these processes duration and intensity do not modify slow component until threshold of combined duration and intensity –After 20 min and 80% –We observe a 5 fold increase in the volume of the slow component

8 Energy Stores Both phosphagens (ATP, CP) and glycogen are depleted with exercise ATP/CP - recover in fast component –measured by sterile biopsy, MRS –rate of PC recovery indicative of net oxidative ATP synthesis (VO 2 ) –study of ATP production mmol/L/min glycogen and all fuels during exercise –CP can drop to 20%, ATP to 70 % –CP lowest at fatigue, rises immediately with recovery Fig very rapid recovery of CP –30 sec 70%, 3-5 min 100% recovery

9 Phosphagen Recovery(cont.) Fig 3.3 –occlusion of blood flow - no phosphogen recovery –** requires aerobic metabolism –estimate 1.5 L of oxygen for ATP-PC recovery Energetics of Recovery Fig 3.4 –breakdown carbs, fats some lactate –produce ATP which reforms CP –high degree of correlation between phosphagen depletion and volume of fast component oxygen Fig. 3.5 –Strong correlation between phosphagen depletion and volume of the fast component of recovery oxygen - sea level and altitude anaerobic power in an athlete related to phosphagen potential - Wingate test

10 Glycogen Re-synthesis Requires 1-2 days - depends on –type of exercise and amount of dietary carbohydrates consumed Two types of exercise investigated –continuous endurance (low intensity) –intermittent exhaustive (high intensity) Continuous-( low-moderate intensity) Fig diet effect –minor recovery in 1-2 hours, does not continue with fasting –complete re-synthesis requires high carbohydrate diet ~ 2 days –Recovery does not occur without high carbohydrate diet –depletion of glycogen related to fatigue –Fig heavy training

11 Glycogen Re-synthesis Intermittent (high intensity) exercise Fig 3.8 –significant re-synthesis in 30 min-2 hrs does not require food intake –complete re-synthesis does not require high carbohydrate intake only ~ 24 hrs for 100 % recovery –rapid recovery in first few hours Continuous vs. intermittent –amount of glycogen depleted Much higher with long duration –precursor availability lactate, pyruvate and glucose available after high intensity exercise –Muscle fiber type involved in activity re-synthesis is faster in type II fibers which are utilized with higher intensity activity

12 Lactate Recovery Blood lactate levels are fairly constant with rising intensity until a threshold of intensity is reached (10.1b) –After threshold, [lactate] rises sharply with intensity –[Lactate] is influenced by the duration of exercise and rest intervals between repeated bouts –Fig lactate turnover fig exhaustive exercise –~25 min for 1/2 recovery (passive) passive recovery - minimal activity Fig 3-11 active vs passive recovery Fig 3-12 intensity of active recovery –untrained % VO 2 Max –trained up to 50-60% - in some studies –glycogen re-synthesis is slowed with higher intensity active recovery

13 Recovery fig (fate of lactate) Fig 3.14 (lactate vs slow component) –close association between the slow component of O2 recovery and the removal of lactate - but not exact restoration of O2 stores –fast component seconds Ion concentrations –pH - rapid return after light exercise –heavy exercise dec. From –~20 min for recovery –close correlation to lactate and fatigue –Recovery of Maximum Voluntary Contraction correlates with Pi (both factors are restored in ~5 min)

14 Performance Recovery How quickly do we regain performance? - force, power, MVC Guidelines Table 3.2 –Dependant on energy system utilized Intensity of exercise and type of recovery Aerobic fitness (VO 2 max) is an important influence as well –good correlation between fast recovery of muscle function and VO 2 max why? –Fast component requires O2

15 Lactate Shuttles Intracellular lactate shuttle (Brooks p 69) –Within one cell –evidence of LDH in mitochondria of muscle, liver and other cells –evidence that mito in liver and heart oxidize lactate more than pyruvate –lactate- more than pyruvate - is link between glycolytic and oxidative met Fig 5-13, 14 (Brooks) –rapid glycolysis -creates a rise in cytosolic lactate –lactate enters mitochondria via MCT pyruvate/lactate carrier (Brooks p79) –oxidized to pyruvate in mito –continues through TCA (Krebs) –NADH formed inside mitochondria, as well as recycled in cytosol

16 Intercellular Lactate Shuttle Between different cells (Brooks p 78) Lactate actively oxidized - preferred fuel in heart and slow twitch muscle produced in Type IIb fibers –transported directly between cells in same muscle –or through blood circulation to type I fibers or heart muscle cells Fig 5-20 (Brooks)

17 Muscle as Consumer of Lactate P (Brooks) Similar to discussions in Foss EPOC - Excess post-exercise oxygen consumption- instead of Recovery Oxygen Causes for excess oxygen used in recovery –13 % increase in BMR / degree Celsius similar to Q10 effect –Fig uncoupling of mitochondria - inc ATP needs –Calcium- accumulates with contraction - mitochondria may sequester Ca++- ATP required to remove it, which may alter net oxidative phosphorylation

18 Endurance Training Table 6-1, 6-2 With endurance training, we observe a doubling of enzyme activity –TCA and ETC - in all muscle fiber types a doubling of mitochondrial content Table 6-3 –improvements in oxidative capacity correlate with running endurance ~ 90 percent correlation –Correlation between oxidative capacity and VO 2 max is not as strong ~ 70 percent correlation ~ % increase in VO 2 max with training vs. ~100% for oxidative capacity With increased mitochondrial content –A given rate of O2 consumption can occur at a higher ATP/ADP ratio –Fig 6-13 –reducing carbohydrate breakdown in favor of lipid metabolism

19 Anaerobic Threshold? Brooks p 215 Historically, the non linear rise in blood lactate at ~60% VO 2 Max was termed anaerobic threshold –does not however provide info about anaerobic metabolism –reflects balance between lactate entry and removal from blood (turnover) –Lactate inflection point is now the preferred term Inflection often corresponds to ventilatory threshold –(non linear rise in ventilation) (talk test) However; Fig –Patients with McArdles syndrome lack of phospohorylase - unable to breakdown glycogen –Have normal ventilatory threshold Association, therefore, is not causal

20 Lactate Inflection Point Many factors may influence either the production or removal of lactate Type II b fiber recruitment - increases with intensity - results in higher lactate production Symp NS activity increases with intensity of exercise –vasoconstriction (many tissues) –Leads to reduced oxidation of circulating lactate - ie. less removal *local factors (paracrines) in muscle –Stimulate vasodilation –raises % of Cardiac Output to working muscle Epinephrine and glucagon –inc glycogenolysis and glycolysis –higher lactate production inc Calcium with contraction - activates glycogenolysis - (Fig 10-18)

21 Learning Objectives Understanding of metabolic influences in glucose fatty acid cycle Distinction between fast and slow components of recovery oxygen –What contributes to the volume of each component Pathways for recovery of energy stores - –Phosphagens, glycogen Recovery of resting lactate concentrations –Active vs passive recovery Performance recovery –Force, power, MVC Lactate shuttles –Oxidative use of lactate - intra vs inter cellular Training impacts on fuel use and recovery Influences on lactate inflection point