Rigor Mortis is caused by muscles fibers running out of ATP that would have let the muscle finish itscontraction.12. Describe in detail the 4 factors that influence the strength of muscle contractions. Metabolic condition-the shape your muscles are in. Amount of load-is the stretching of muscles before lifting. Length-tension relationship- Refers to the length at which a muscle can produce the greatest force. Recruitment of motor units-is the bringing into activity of additional motor neurons, which causes additional muscle fibers to contract.13: Phases of a muscle contraction.A muscle contraction in response to a single nerve action potential is called a twitch contraction. Amyogram, a graph of muscle strength (tension) with time, shows several phases, shown in Figure 1: 1. The latent period is the time required for the release of Ca2+. 2. The contraction period represents the time during actual muscle contraction. 3. The relaxation period is the time during which Ca2+ are returned to the sarcoplasmic reticulum by active transport. 4. The refractory period is the time immediately following a stimulus. This is the time period when a muscle is contracting and therefore will not respond to a second stimulus. Since this is occurring at the same time as the contraction, it does not appear on the myogram as a separate event. (1)14: Treppe Effect The concept or phenomenon of "Treppe" occurs when a muscle contracts more forcefullyafter it has contracted a few times than when it first contracts. This is due to the fact that activemuscles require decreasing degrees of succeeding stimuli to elicit maximal contractions. Returningto our example of the second set of squats feeling easier than the first, during the first set there wasinsufficient warm-up, and the second set felt easier because the first set actually served as a warm-up. The phenomenon in which the contraction strength of a muscle increases, due to increasedCa2+ availability and enzyme efficiency during the warm-up. (1)Golfers need to warm-up too; all that practice is what makes a golfer’s movements so fluid.