Sports Physiology Exercise Physiology Improvements through training

Muscle Fiber Type Slow Twitch (Endurance) Fast Twitch a (Intermediate) Fast Twitch b (Sprints) Make-up of calf muscle…a comparison Marathon runner - 90% Slow Twitch Sprinter - 25% Slow Twitch

Slow Twitch, Fast Twitcha, Fast Twitchb comparison ST FT a FT b Oxydative Capacity High Moderately High Low Glycolytic Capacity Low High Highest Contraction Speed Slow Fast Fast Fatigue Resistance High Moderate Low Muscle Fiber Low High High Strength

Let’s Play the Muscle Fiber Game! Slow twitch or Fast twitch?

I – Slow-twitch II – Fast-Twitch

Energy Systems (source of ATP for cross bridge formation) Phosphagen System (10 seconds) Stored ATP – 3 secs 4 moles ATP/min Phosphocreatine – 7 secs Glycolytic System (1-2 minutes) Glycolysis 2 moles ATP/min Inefficient but fast Buildup of Lactic acid – must be buffered Oxydative (aerobic) (indefinite) Very efficient 1 mole ATP/min

Capacity of Energy System vs. Exercise Duration

Fiber Type Recruitment Order (As you increase the effort you recruit more numbers of fibers but what about fiber type?) Low intensity (walk; slow jog) slow twitch Medium intensity (fast jog; run) slow twitchfast twitch a High intensity (run; sprint) slow twitch & fast twitch a  fast twitch b

Oxygen and Fuel Oxygen Fuel Glucose Fat Protein From blood Stored bound to myoglobin Fuel Glucose From blood (liver make it from glycogen) Stored in muscle (glycogen) Fast delivery rate Fat Very abundant energy source! Slow delivery rate Protein Abundant but not ideal source

Oxygen Debt

Tchotchke, Tchotcholate Tchallenge!

Assuming no change in physical activity, what would happen to the partial pressure of oxygen in veins of the systemic circulatory system if cardiac output were increased by a factor of 2?

Fatique Energy Depletion Buildup of Metabolic Byproducts Phosphocreatine (short, hard efforts) Glycogen Depletion (longer efforts) Buildup of Metabolic Byproducts Lactic acid Inhibits glycolytic enzymes Inhibits crossbridge formation (H+ interferes) Nervous System Mostly Psychological***

Can I Keep Going?

Endurance Training Increased Vascularization – more capillaries Increased Myoglobin More Mitochondria More Oxydative Enzymes Psychological factors Become comfortable with/embrace pain & discomfort

Anaerobic Training (increase Anaerobic Threshold and increase Anaerobic Capacity) More Glycolytic Enzymes Increased Capacity for Lactic Acid More blood More bicarbonate Increased ability of liver to metabolize lactic acid Psychological Factors Deal with Pain

A common nonsense polymorphism (R577X) in the ACTN3 gene results in complete deficiency of the fast skeletal muscle fiber protein a-actinin-3 in an estimated one billion humans worldwide. The XX null genotype is under-represented in elite sprint athletes, associated with reduced muscle strength and sprint performance in non-athletes, and is over-represented in endurance athletes, suggesting that a-actinin-3 deficiency increases muscle endurance at the cost of power generation. Here we report that muscle from Actn3 knockout mice displays reduced force generation, consistent with results from human association studies. Detailed analysis of knockout mouse muscle reveals reduced fast fiber diameter, increased activity of multiple enzymes in the aerobic metabolic pathway, altered contractile properties, and enhanced recovery from fatigue, suggesting a shift in the properties of fast fibers towards those characteristic of slow fibers. These findings provide the first mechanistic explanation for the reported associations between R577X and human athletic performance and muscle function.

A common nonsense polymorphism (R577X) in the ACTN3 gene results in complete deficiency of the fast skeletal muscle fiber protein a-actinin-3 in an estimated one billion humans worldwide. The XX null genotype is under-represented in elite sprint athletes, associated with reduced muscle strength and sprint performance in non-athletes, and is over-represented in endurance athletes, suggesting that a-actinin-3 deficiency increases muscle endurance at the cost of power generation. Here we report that muscle from Actn3 knockout mice displays reduced force generation, consistent with results from human association studies. Detailed analysis of knockout mouse muscle reveals reduced fast fiber diameter, increased activity of multiple enzymes in the aerobic metabolic pathway, altered contractile properties, and enhanced recovery from fatigue, suggesting a shift in the properties of fast fibers towards those characteristic of slow fibers. These findings provide the first mechanistic explanation for the reported associations between R577X and human athletic performance and muscle function.

Cost of Transport

1 m/sec = 2.24 miles/hr

Endurance running and the evolution of Homo Human Nature 432, 345-352 (18 November 2004) | doi:10.1038/nature03052; Received 25 July 2004; Accepted 23 September 2004 Endurance running and the evolution of Homo Dennis M. Bramble1 and Daniel E. Lieberman2 H. erectus Australopithecus afarensis [uh-fah-ren-sis] Chimp A.afarensis