Leaps Lab

In this experiment the results we obtained correlated with each hypothesis given. The effect on our muscles when fatigued or having gone thru environmental changes such as temperature, changed the pace at which our muscles were able to perform. In this discussion you will be able to understand in detail the how’s and why’s of this experiment and their results.

In Test A the physical changes from a relaxed state to a flexed state were visible specifically to our group in three identifiable ways. First, the circumference increased when the muscle contracted. Second, the rigidity of the biceps brachii from relaxed to contracted you can feel the hardness of the muscle. and lastly, when the muscle contracted, the muscle shortened. The type of muscle contraction that took place in Test A is known as a isotonic concentric contraction. This is a type of muscle contraction in which the muscles shorten while generating force. This is typical of muscles that contract due to the sliding filament mechanism as we stated in the introduction, “1) During a contraction, both the I band and the H zone narrow while the A band remains unchanged. 2) Myosin heads attach to actin to pull thin filaments toward the M line(referred to a the power stroke) that brings Z-discs closer together, which causes the sarcomeres to shorten and a contraction to take place,” and the contraction also alters the angle of the joints to which the muscles are attached, as they are stimulated to contract according again to the sliding filament mechanism. For example, a concentric contraction of the biceps would cause the arm to bend at the elbow as the hand moves from near the leg to the shoulder.

In Test B we tested the effects of a temperature decrease on a muscle. We hypothesized that if the temperature of the muscle is reduced then the muscle response time will increase. Our results showed that a drop in temperature did in fact alter the response time for contraction. Forces developed by muscles and their rates of force generation, contraction, relaxation, and power output are all altered by environmental effects in this case is temperature. There are multiple reasons why muscle contraction requires more work and therefore takes longer to produce when affected by temperature changes. If you have ever felt your muscle and joints feel stiff in the cold, it is due to lack of oxygen in the muscle. Oxygen plays a big role in muscle contraction, the rate at which oxygen molecules become unbound from hemoglobin affects that amount of oxygen that reaches the muscle. A greater force such as contraction requires a larger supply of oxygen. The temperature changes affects the ease at which oxygen is being released, causing the muscle to take longer to contract. Another reason that Grayson’s muscle slowed down after it had been submerged in water is a reaction of the reduction in blood flow. When your body receives signals that a decrease in temperature is taking place, your blood vessels constrict which limits the amount of blood that flow to the skin’s surface. Instead, the blood flow is redirected internally to keep the core of your body at a regulated homeostatic temperature.

In Test C, our group tested the effects of Clayton’s muscle after 10 sets of 20 second continuous repetitions of squeezing a tennis ball. Our results were as predicted, if the muscle is not given rest between contractions, then the muscle will not work at optimum level. To fully understand how fatigue affects the muscle it is important to know where your muscles energy comes from and how fatigue is brought on. Muscle contractions are fueled by ATP(adenosine triphosphate) a molecule that stores energy. There are 3 substances adapted from ATP that is used as our energy source; Free ATP, glycolysis, phosphocreatine, and cellular respiration. Free ATP generates enough energy for only about 10 seconds of muscle activity. Glycolysis happens as a series of reactions that breaks glucose down to pyruvate immediately following Free ATP. Pyruvate can replenish energy levels for only 30-40 seconds of muscle activity If oxygen is available pyruvate becomes 1 ATP, however if oxygen is lacking, pyruvate will forms into 2 molecules of lactic acid. Cellular respiration will follow and while the pyruvate generated through glycolysis can accumulate to form lactic acid, it can also be used to generate further molecules of ATP.

Mitochondria in the muscle fibers can convert pyruvate into ATP in the presence of oxygen via the Krebs Cycle, generating an additional 30 molecules of ATP. Cellular respiration is not as fast as the above mechanisms; however, it is required for exercise periods longer than 30 seconds. Cellular respiration is limited by oxygen availability, so lactic acid can still build up if pyruvate in the Krebs Cycle is insufficient. In both glycolysis and cellular respiration, lactic acid has the ability to continuously build up. Muscle fatigue is the decline of muscle force generation over time, the reason for this is a in large part to the lactic acid build up. This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.

This further inhibits anaerobic respiration, inducing fatigue. In our test as you will see in our results, Clayton’s squeezes per trial declined as we had hypothesized however, trials 9 and 10 his number of squeezes doubled and remained fairly constant for two trials. After the test was completed he informed us that during trial 9 he popped the tennis ball while squeezing. After he popped the ball, it became not only easier to create more squeezes, it also gave him a jolt of energy. Have you ever heard of someone suddenly finding a jolt of strength right before the end of a race? This is thanks to epinephrine, or as most people recognize “adrenaline.” Adrenaline is produced in the medulla in the adrenal glands and also parts of the CNS. It triggers the fight or flight response, this reaction causes air passages to dilate and provide the muscles with the oxygen it needs to fight or flee.

This causes a noticeable spike in strength and performance, but adrenaline is not permanent as it typically only lasts a few minutes, up to an hour. It is difficult to say for certain that adrenaline was in fact what Clayton was feeling on trials 9 and 10 or he simply was able to make more squeezes due to the release of tension from the popped tennis ball. For anyone recreating this experiment for themselves and they come across this same instance, I would strongly suggest repeating Test C until you have completed all 10 trials with the tennis ball intact.