Muscle Mechanics (1) Flashcards
Explain what is happening at the cellular level during the 4 stages of an isotonic twitch
See pg. 316 for figure
- Isometric tension development
- Isotonic shortening
- Isotonic relaxation
- Isometric relaxation
Define velocity of shortening. Describe force versus velocity relationships for a skeletal muscle at different loads
Velocity of shortening = slope of shortening curve or first derivative. When load is light velocity is high & when load is heavy velocity is slow.
Since velocity is slope of shortening curve , high slope or high velocity occurs @ light weight & it slows @ heavier weight.
See pg. 317
Using the length-tension diagram to calculate the work generated during an isotonic contraction
Do problems on pg. 323
Explain what an isometric contraction is and describe its physiological relevance
When a muscle develops tension, but stays the same length because its ends are attached to immovable objects, the contraction is said to be isometric. Even though the length of the muscle is constant during the contraction, the tension increases. Isometric contractions are involved in maintaining posture (e.g., latissimus dorsi). Tension changes & muscle length stays constant.
Isometric contractions do no work & have no power, but still has tension: In an isometric contraction, since the muscle length is constant, and the load is not moved, no external work is performed. Since no work is done during an isometric contraction (dW=0), the power is also zero.
Too heavy a load cannot be lifted at all, which represents an isometric contraction.
Work =
Work = FΔd
Work equals Force (F) times the Distance an external object is moved (∆d), equivalent to the change in length of the muscle (W = F x Δd).
Power =
Work/ time = FΔd/ t
Explain what an isotonic contraction is and describe its physiological relevance
In an isotonic contraction, tension is kind of constant (low to high then constant to low tension–isotonic high tension when actually lifting) and the muscle’s length changes (DB bicep curl). You actually move things. Isotonic contractions do work & have power. Isotonic = isotension.
Integration of isometric & isotonic contractions
Most coordinated movements of the body involve a combination of isotonic contractions in some muscles and isometric contraction in other muscle.
Moving a heavy textbook requires that some muscles (e.g, the bicep) produce movement while other muscles (e.g., the back muscle – latissimus dorsi) increase postural rigidity in preparation for the increasing loads caused by lifting the massive text.
Myofibers produce maximum work & power @
Intermediate loads and intermediate velocity of shortening
Preload
Preload – For skeletal muscle, the preload is a weight that pulls the muscle to a given INITIAL length. It is the load that is required to stretch the muscle into its operating range.
Afterload
Afterload – For skeletal muscle, the afterload is equivalent to the total tension.
Total load =
Total load = Preload + Afterload
NOTE that total load = maximum tension on the graph, so do not subtract preload for total load!
Describe positive & negative work
During the rising phase where the load is raised at constant velocity the muscle is performing positive work. The rising phase is called a concentric contraction. The time in the denominator for power is only the time for positive work since the net distance would be zero if you did it for both positive & negative work.
During the declining phase when the load is lowered at constant velocity the muscle is technically performing negative work. This is called an eccentric contraction and again, by convention, the work performed is negative.
