1. Exercise Metabolism Concepts Dr. Suzan Ayers Western Michigan University

2. Lecture Overview  Energy production  Oxygen supply during sustained exercise  Measuring exercise capacity  Cardiorespiratory system and oxygen supply during exercise  Human skeletal muscle cells  Activity’s energy cost  Dietary considerations  Sport-specific training NOTE: throughout this presentation, the use of [] connotes “concentration”

3. Energy Production  Adenosine triphosphate (ATP)  3 ATP-resynthesizing energy systems (Fig 10.4) Immediate energy system (stored energy, high-energy phosphagen, ATP-PCr system) 0-30s Anaerobic glycolytic system (lactic acid system) 20-180s Aerobic or oxidative system >3 min (see Table 10.1) All work along a continuum (fig 10.4) constantly Body breaks down nutrients (fats, proteins, carbs) to release energy from chemical bonds, which is then used to synthesize ATP Max exercise can produce 15-fold ↑ [lactic acid]  20-40 mins required to fully remove this lactic acid build-up  Light jog @ 30-60% max pace best active recovery

4. Oxygen Supply: Sustained Exercise  Oxygen consumption: VO 2  O 2 deficit initial few mins of exercise, insufficient O 2 uptake ATP provided by 2 anaerobic systems Period of adjustment for increased energy demand  Submaximal, [ ↔ ] exercise VO 2 steady state reached  Continually [>] exercise VO 2 increases steadily to max value/exercise capacity

5.  Supramaximal exercise (above VO 2 max) ATP, beyond that produced by oxidative metabolism, produced by anaerobic glycolysis ( ↑ lactate levels )  Post-exercise O 2 uptake EPOC: excess post-exercise O 2 consumption ( O 2 debt) Excess O 2 removes lactate & re-synthesizes muscle stores of glycogen, PCr and ATP Size of EPOC depends on [exercise]/duration  VO 2 max: Indicator of endurance ex capacity Max O 2 consumed/min during exercise (aerobic power) 40-50% genetically determined May increase up to 40% w/ training Not exclusive indicator of exercise performance

6. Measuring Exercise Capacity: Aerobic or Endurance Capacity  VO 2 max: measure of aerobic power  Endurance exercise capacity: performance measure  Mode of testing specific to athlete’s training  VO 2 max usually reached during final minute of exercise, immediately before volitional fatigue Major limiting factor for endurance exercise performance is O 2 delivery via the circulatory system to the working muscles

7. Measuring Exercise Capacity: Anaerobic Capacity  Anaerobic power: max power, possible in all-out exercise test  Anaerobic capacity: total work accomplished in a set time (30-60s)  General or sport-specific tests used 10- and 30-s cycle ergometer tests Vertical jumping Sprinting Stair climbing Both (an)aerobic tests help standardize [exercise] for exercise prescription

8. Cardiorespiratory System and Oxygen Supply During Exercise  Cardio: heart  Vascular: blood vessels  Respiratory: lungs and ventilation  Aerobic: with oxygen  Overall, HR, blood flow, & respiratory rate ↑ proportionally with ↑ [exercise]  Blood flow during submax exercise, ~50-60% of blood flow is directed to working muscles during max exercise, ~80% of blood flow is directed to working muscles

9. Human Skeletal Muscle Cells  Fiber types are classified by (Table 10.2) : Physiological (activities, functions) Biochemical (chemistry of biological processes) Histological (microscopic structure) properties  Motor neuron determines fiber type I (slow oxidative): smaller, ↓ force, ↑ time, posture IIa (fast oxidative glycolytic): large, fast, ↑ force, ↑ gylcolytic capacity, moderate: mitochondria, capillary supply, oxidative capacity than IIb fibers IIb (fast glycolytic): largest, fastest, most forceful, ↑ anaerobic glycolytic capacity, fatigue easily

10.  Fiber types activated proportionally to force Size principle:  I, then IIa, then IIb (as additional force needed)  Average human: 50% ST, 50% FT  Proportion of fiber types varies Elite distance runners: 80% I, 20% II Elite sprinters: 25-40% I, 60-75% II  Fiber types only a broad indicator of potential

11. Activity’s Energy Cost  Influential factors Activity, intensity, mechanical efficiency Body mass (non-supported activities-run, walk) Environmental factors (temperature, wind, rain)  Human body, at best, 25% efficient Economy of movement: O 2 cost of any activity Body mass supported: energy cost independent of body mass Unsupported activities: energy cost rises w/ ↑ body mass Most energy consumptive: whole body or large muscle group activities (swim, run) Consider energy cost of training in development of dietary planning

12. Dietary Considerations  High carbohydrate (CHO) diet ↑ muscle glycogen stores (ergo exercise capacity) Fig.10.14 “Hitting the wall”=glycogen depletion 24-48hr required to fully restore glycogen levels ↑ CHO diet ASAP after exercise aids repletion rate  Sports drinks, fruits, breads, wheat cereals, gels 60-80% daily intake=CHO  6-8g CHO/kg body wt/day Intense training or taper times  9-10g CHO/kg body wt/day

13.  Protein Tables 10.4, 10.5 Well-balance diet adequate for most athletes 12-15% daily intake=protein (0.8g protein/kg/day) Strength/Power/Speed athletes  1.5-2 g protein/kg body wt/day Endurance athletes  1.5-1.6 g protein/kg body wt/day EXCESS PROTEIN = EXPENSIVE URINE

14.  Water 70-80% energy produced during ex is heat (sweat) Depending on factors, 0.5-3L/hr sweat can be lost Losing 4-5% body mass impacts thermoregulation and exercise capacity Prolonged exercise w/o H 2 0 replacement  Blood volume may drop significantly  Heat loss slows/stops  Body temp can ↑ dangerously Guidelines  500-1000ml pts plain H 2 0 1hr before activity  250-500ml 20 mins before  250ml every 15 mins during  Intense exercise > 60 mins: add glucose & electrolytes  6% glucose in solution--[low electrolyte] promotes faster H 2 0 absorption  Several hrs may be needed to completely replace H 2 0

15. Sport-Specific Training  Anaerobic Energy Training Max force production (Abernathy:0-30 sec)  Stored ATP and PCr, muscle glycogen breakdown Anaerobic glycolysis  Up to 2 min events (Abernathy:20-180 sec) Limited support for training benefits here

16.  Aerobic Energy Training (Abernathy:0-30 sec) Evidence clear, dramatic, specific Endurance training has specific benefits  ↑ mitochondrial volume in muscle  ↑ enzyme activity in aerobic pathways  ↑ fiber’s ATP generating ability aerobically  ↑ # capillaries fueling each muscle fiber  ↑ intramuscular fat stores  improves fat burning ability  Improves muscle’s ability to access & utilize fat

17. Endurance training has general benefits  ↑ blood volume 10-15%  ↑ stroke volume  ↑ cardiac output (HR x stroke volume)  ↑ efficiency of the respiratory system  More air with fewer breaths  Greater tidal volume  Ventilation=tidal volume x frequency