PowerPhys:Activity 2 Twitch Contractions and Summation Essay

O B J E C T I V E S 1. To define these terms used in describing muscle physiology: multiple motor unit summation, maximal stimulus, treppe, wave summation, and tetanus. 2. To identify two ways that the mode of stimulation can affect muscle force production. 3. To plot a graph relating stimulus strength and twitch force to illustrate graded muscle response. 4. To explain how slow, smooth, sustained contraction is possible in a skeletal muscle. 5. To graphically understand the relationships between passive, active, and total forces. 6. To identify the conditions under which muscle contraction is isometric or isotonic. 7. To describe in terms of length and force the

The lab chart was then stopped once the 5s contraction period had ended. Then the maximum force in Neutons (N) for that trial was calculated by the chart. The 5s MVC procedure was then repeated two more times and the MVC for each trial was calculated by the chart software and the highest MVC contraction and MVC for each trial was then identified and all the values were out into table 1.5. Then each participant 90% MVC was calculated by taking the 100% MVC and multiplying it by 0.9 which was then put into the second table, and the guideline of the participants 90% max was then put into the lab chart. The participant then prepared to hold their 90% MVC for 1 minute. With their knee already extended as far as they could without contracting with no slack in the line or chain the lab chart was started and the participant was instructed to kick out to achieve maximal force and tried to hold it for 1 minute to the best of their abilities and then relax when the minute has

Every time our body moves, our muscles contract. As the muscle contracts, the muscle becomes fatigued; unable to maintain force output. There are two types of fatigue; central and peripheral (1). Central fatigue involves the central nervous system, whereas peripheral fatigue includes fatigue outside of the central nervous system in the muscles (5). Changes to these systems affect the rate at which the muscle fatigues, including the speed of contraction, the strength of the load, and feedback (5). Therefore, the purpose of this study was to determine whether increased force would influence the time of fatigue, with and without visual feedback. It was hypothesized that as the magnitude of force increased, the time to fatigue would decrease, whereas while the magnitude of force decreased, the time to fatigue would increase. Overall, visual feedback would have increased time to fatigue, compared to non-visual feedback, which would have decreased time to fatigue.

The amplitude of the muscle contraction increased as the voltage increased until a threshold was met.

Fast muscle fibers (fast twitch) contract more quickly and powerfully and fatigue easily, short burst intense activity weight lifting or sprinting. ATP production, anaerobically, thicker

Nerves are responsible for the controlling the contraction of muscles, determining the number and the sequence and force of muscle contractions (Muscle Fatigue, 2015). The movements that are required for a force far below what a muscle is able to generate and with the exception of pathology nervous fatigue is seldom an issue. For extremely powerful contractions that are close to the upper limit of a muscle’s ability to generate force, nervous fatigue can be limiting factor in untrained individuals.

To fully understand the mechanisms that cause graded muscle contractions, the effects of fatigue, twitch summation, twitch recruitment, tetanus and muscle stretch on skeletal muscle were observed. The gastrocnemius muscle of the Rana pipiens frog was used for each of the 5 experiments performed. When twitch recruitment was observed, one trial was conducted by stimulating the sciatic nerve and the other, conducted by stimulating the skeletal muscle. The contractile force of the muscle was increased until reaching its maximum amplitude. This occurred at a preload of 0.37 (N) raw twitch of 0.39 (N). Optimal length was concluded to be greater than or equal to 5.9 mm, but an exact value was not found due to limitations on stretching. Summation was studied by decreasing inter-stimulus intervals until two twitches summed together. This occurred at 100ms, the point where two twitches could no longer be differentiated. One trial was run at different pulse intervals at 500mV to observe tetanus. Tetanus occurred

While the impulse generated by a single motor unit is quite weak, the combination of several can be detected by surface electrodes (EMG) (Michell, 2011). This is coupled with the measurement of power (DYN). When all of the available motor units are recruited at maximum strength, the muscles will fatigue rather quickly. However, when only a few of the motor units are recruited, the muscles will take more time to fatigue as the motor units will use those that are in reserve whenever one reaches fatigue (MacIntosh, Gardiner & McComas, 2006).

In order to stimulate all muscle fibers in an area, the stimulus must have a high voltage. However, there are a limited number of muscle fibers within each muscle, so there is a limit on how great the force of the contraction can be (Sedava et al, 2014). I hypothesized that if the stimulus applied to the muscle increases in voltage, then the force of the contraction will increase in strength until it reaches its maximal force where all individual muscle fibers will be recruited. This hypothesis was tested by delivering stimuli of increasing voltages to the muscle and recording the corresponding contraction forces (Holbrook et al, 2017). Through observation of the contraction and graphing the recorded values, it was possible to determine whether the results followed the

3. How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Are these results called treppe or wave summation? How well did the results compare with your prediction?  When the stimulation frequency was increased to the point in which muscle relaxation did not occur the amount of force progressively increased with each stimulus.  When muscle twitches overlap, no muscles relax, and stimuli occurs one after another in a short amount of time, the muscle contraction is higher than if a single stand alone contraction had occurred

Slow-twitch muscle fibers contract the slowest out of all of the muscle fibers. This is because they do not have a large amount of myosin ATPase and therefore, cannot split ATP at a fast rate. This slow contraction causes them generate much less force than fast-twitch muscle fibers (Silverthorn, 2009). Slow-twitch muscle fiber contractions last an extended period of time because the calcium is not recycled quickly by the SR (Silverthorn, 2009). This makes them ideal muscles for maintaining posture. Slow-twitch muscle fibers also do not fatigue easily due to the presence of large amounts of mitochondria and capillaries. Since they rely on aerobic respiration to create energy, the presence of many mitochondria allows large amounts of energy to be generated, keeping the muscle energized for long periods of time (Silverthorn, 2009). Slow-twitch

The expansion in size of muscle is alluded to as hypertrophy. The "pump" one feels from a solitary activity session is alluded to as transient hypertrophy. This fleeting impact is inferable from the liquid aggregation, from blood plasma, in the intracellular and interstitial spaces of the muscle. Conversely, interminable hypertrophy alludes to the expansion in muscle size connected with long haul resistance preparing. Increments in the cross-sectional territory of muscle filaments range from 20% to 45% in most preparing studies (Staron et al., 1991). Muscle fiber hypertrophy has been appeared to require more than 16 workouts to create huge impacts (Staron et al., 1994). Furthermore, quick jerk (glycolytic) muscle fiber can possibly indicate more noteworthy increments in size when contrasted with moderate jerk (oxidative) muscle fiber (Hather, Tesch, Buchanan, and Dudley, 1991).

1.) In the article by Duchateau, Semmler & Enoka, they explained the importance of the behavior of single motor units that follow training. The Motor Unit is a vital part in both strength training and skill training. The motor unit is comprised of a motor neuron in the spinal cord, its axon and all of the fibers that innervates. Motor unit’s main function is to transform synaptic input that is received by the motor neuron. On average, 300 muscle fibers are innovated, however, the range can extend far beyond that median number. Muscle fibers have many varieties that are affected through levels of fatigue, force and contraction speed. The most important is the size of the motor neuron. The influence of the size creates

When performing many feats of physical skill, calculating how fast a person can perform the action has become a custom that has gained prominence in recent years. Observing how long it takes a person to perform an action, now known as observing the reaction time, has even gained enough importance to the point that it has even used in some scientific investigations. The purpose of this scientific investigation, for instance, is to test whether or not an outside force, such as music, will affect the reaction time of any given test subject. Whether the change will be a positive one, such as helping

The strength of a muscle is proportional to the surface area of its cross section.