Metabolism
What is the primary fate of lactate?
To be oxidized.
What does epinephrine stimulate? What does insulin stimulate?
Epinephrine stimulates breakdown (glycogen into glucose, triglycerides into fatty acids,
Insulin stimulates storage (fatty acid, glucose, amino acids into tissues)
What proteins make up the sarcomere?
Contractile proteins: Actin and myosin
Regulatory proteins: Troponin and Tropomyosin
What are the two criteria we can use to visually determine what a muscle fiber is?
SDH (succinate dehydrogenase) and fast myosin
Describe lactate transport
When H+ ions are being accumulated in the skeletal muscles due to ATP splitting, they are able to leave the skeletal muscles by cotransporting with lactate through a symport into the blood.
Why is it important to keep insulin levels low during exercise?
To inhibit storage and ensure that fuel goes to working muscles
What neurotransmitter is released from the presynaptic cell of the neuromuscular junction and binds to ligand gated Na+ channels
Acetylcholine
What inhibits the synthesis of muscle proteins to conserve energy and we want to inhibit it to build more muscle?
Myostatin
Describe the lactate shuttle
How do epinephrine and norepinephrine stimulate the breakdown of glycogen?
Norepinephrine binds to alpha receptors on beta pancreatic cells to inhibit insulin production, which means that glucose will not be taken up by tissues
When released simultaneously, these hormones will make muscles draw upon their glycogen stores for fuel, not the fuel in the blood.
What are the invaginations of the sarcolemma that depolarization moves down and what stores calcium
T-tubules, sarcoplasmic reticulum
What type of muscle fiber has the most glycogen and creatine phosphate stores? What type of muscle fiber has the lowest level of force production and fatigability?
Type 2x and Type 1
How is RER able to reach above 1.0? How does this system work?
RER is able to be above 1.0 due to the bicarbonate buffer system, which is a non metabolic source of CO2 that takes the H+ ions moved into the blood and combines with bicarbonate HCO3- to become carbonic acid, which becomes CO2 and H2O and back.
How does glycogen sparing work?
Epinephrine concentration increases exponentially with exercise intensity, but as we train an untrained person, their epinephrine concentration during exercise decreases, meaning we can stretch out our glycogen reserves for longer and exercise longer
Describe the length-tension principle
As load increases, we need more cross bridges to bind, which causes velocity to slow down because it takes more time. However if we push length too far, no contraction can occur because there is no overlap between myosin and actin
What is responsible for initial strength gain during training and at what point does that source swap to a different source? What is that secondary source?
At what RER would the absolute fat utilization be the highest and why? What would be the relative fat utilization be the highest and why?
0.73, 0.85, 0.97
Absolute fat utilization would be highest at 0.85 RER because the ratio of fat to carbohydrate utilization is 50/50, but more fat is being utilized here than at 0.73 or 0.97. Less relative utilization, but more actual utilization
Relative fat utilization would be highest at 0.73 RER because fat is ~90% of the fuel source being used at this level of intensity, so while it is a smaller amount of fuel being used, fat is the most utilized relative to the whole.
This is the crossover concept in action. As exercise intensity increases, fat utilization will decrease and carbohydrate utilization will increase
Is glycogen completely used up at high intensity exercise? If not, when does it get fully used up
Glycogen is fully used up at 75% of VO2max. It is not used up at higher levels of exercise because we experience exhaustion before glycogen reserves can be exhausted
Describe excitation-contraction coupling from action potential reaching the presynaptic cell to the power stroke
- Action potentials reach the presynaptic cell and release acetylcholine.
- Acetylcholine binds to ligand gated Na+ ion channels and allow sodium into the postsynaptic cell
- The wave of depolarization moves down the sarcolemma down the T-tubules
- Release calcium from the sarcoplasmic reticulum
- Calcium binds to troponin, pulling away tropomyosin, exposing the myosin binding sites on the actin
- Myosin and actin bind, forming a cross bridge, performing a power stroke
What would happen to a person's muscle fibers if we took a sedentary person and started weight training them? What if we chose to start endurance training them?
Their muscle fibers would convert from Type 2x to Type 2a fibers due to increased mitochondrial requirement.
Their Type 1 fiber count would increase and Type 2a and 2x count would decrease due to oxidative requirement