Measuring Metabolic And Electrical Changes For Muscle Fatigue

Muscle Contraction Lab Report

Purpose

The purpose of this lab is to explore the fatigue of muscle contraction by measuring both metabolic and electrical changes over a period of time. We will fulfill these objectives by measuring a subject's continuous grip strength and repetitive grip strength with a Vernier Hand Dynamometer and Electromyogram (EMG) Sensor. Continuous grip strength will quantify metabolic changes, and repetitive grip strength will quantify electrical changes.

Literature review

There are three types of muscle (smooth, cardiac, and skeletal), and this laboratory experiment deals with skeletal muscle, which can be controlled consciously (Godwin et al. 2009). Muscles are made up of muscle fibers, which are cells that are set off by neurons (Godwin et al. 2009). These fibers are made up of myofibrils, and a group of these filaments is called a sarcomere (Moyes and Schulte 2008). Different organizations of myofibrils allow for different amounts of force to be created when the muscle contracts (Moyes and Schulte 2008). Muscle contraction occurs when the membrane depolarizes and there is an increase in intracellular calcium concentration, allowing myosin to bind to the actin and shorten the sarcomeres (Moyes and Schulte 2008). After prolonged muscle contraction, muscle fatigue can occur.

Muscle fatigue is the lowering of the amount of force a muscle can create (Subasi and Kiymik 2010). One reason this happens to the muscle is because of not enough oxygen and other nutrients available within the circulatory system (Cifreka et al. 2009). It is also due to a difference in how effective a person’s nervous system is (Cifreka et al. 2009). Muscle fatigue can become a problem in real world scenarios, especially in relation to physical activities that involve “repetitive tasks” (Subasi and Kiymik 2010), such as repeatedly unloading heavy boxes at a construction site.

There has been a lot of research conducted on the relationship between constant muscle force exerted and muscle fatigue, but not much research has been done on how repeating muscle force relates to muscle fatigue. One study determined how different forms of repeated tasks influenced muscle fatigue (Iridiastadi and Nussbaum 2006). They discovered that performing these tasks using only 20 to 28% of maximum contraction force caused a great amount of muscle fatigue (Iridiastadi and Nussbaum 2006). Experiments on how different types of forces affect muscle fatigue can be valuable to many work fields. Discovering tasks that can be repeated while fatiguing the muscles at a slow rate would be helpful to minimize the amount of injuries in the workplace and more effectively get the job done.

This experiment will use a Vernier EMG Sensor to measure the electrical data. This sensor gives off a signal when it detects action potentials that muscles make while contracting (Raez et al. 2006).

Hypothesis

I hypothesize that nerve based fatigue will occur quicker than metabolic fatigue.

Materials and Methods

In this experiment, one subject’s muscle force was measured using a Vernier Hand Dynamometer. First the Hand Dynamometer and EMG Sensor were assembled and plugged into the computer. The Vernier computer interface was opened on the computer. The duration was switched to 100 seconds, and the Hand Dynamometer readings were zeroed. The Logger Pro electrode tabs were placed on the subject’s arm: two on the forearm and the third on the upper arm. The green and red clips were attached to the electrode tabs on the forearm, and the black clip was attached to the electrode tab on the upper arm. The subject sat with a straight back and arm bent parallel to their legs.

To start gathering the data, the green play button was pushed and the subject squeezed the Hand Dynamometer with as much force as they could for 100 seconds. After 80 seconds passed, the subject squeezed the Hand Dynamometer tighter.

On the Vernier computer interface, statistics were collected from the Grip Strength graph. The average force was recorded for the intervals 0 to 20 seconds, 60 to 80 seconds, and 80 to 100 seconds. Statistics were collected from the EMG graph. Maximum and minimum millivolt (mV) were recorded for the same time intervals. The difference between maximum and minimum mV for each interval were recorded. The slope from 0 to 100 seconds was recorded from the Grip Strength graph.

The subject then sat in the same position as before, holding the Hand Dynamometer upright. For 100 seconds, the subject squeezed then relaxed the Hand Dynamometer, repeating this motion two times per second. After 80 seconds passed, the subject squeezed the Hand Dynamometer with more force, continuing the repetitive motion.

On the Vernier computer interface, statistics were collected from the Grip Strength graph. The average force was recorded for the intervals 0 to 20 seconds, 60 to 80 seconds, and 80 to 100 seconds. Statistics were collected from the EMG graph. Maximum and minimum millivolt (mV) were recorded for the same time intervals. The difference between maximum and minimum mV for each interval were recorded. The slope from 0 to 100 seconds was recorded from the Grip Strength graph.

Results

Figure 1.

Figure 1 shows the differences between the continuous and repetitive grip forces of different subjects. The continuous grip force is over 75 N and under 300 N. The repetitive grip force does not go above 225 N. A majority of the subjects have similar measurements of continuous and repetitive grip forces. The orange subject has the highest continuous force, about 300 N, and the lowest repetitive force, about 40 N. Five of the subjects remained in the range of 75 to 200 N for both types of grip (Question 2).

Figure 2.

Figure 2 shows the slopes of continuous and repetitive grip types for different subjects. Measurements for both grip types are about the same for each subject. A majority of them are negative. Slopes for repetitive grip are grouped closely together near zero. Slopes for continuous grip are more spread out and more negative. Subject 1 is an outlier with both grip types being positive ranging from 2 to 3.

Figure 3.

Figure 3 shows the average grip strength (N) of both continuous and repetitive grip during three different time ranges. The highest average grip strength for both grip types is from 80 to 100 seconds. Continuous has a measurement of 83.6 N and repetitive has a measurement of 52.9 N. In the time intervals 0 to 20 seconds and 80 to 100 seconds, continuous grip has a higher average strength. The lowest average strength for both grip types is from 60 to 80 seconds. Continuous has a measurement of 30.7 N and repetitive has 33.1 N.

Figure 4.

Figure 4 shows the EMG Sensor readings for the change of mV of continuous and repetitive grip types. For all time intervals, continuous grip has a smaller difference between maximum and minimum mV. The largest difference for both grip types is from 80 to 100 seconds. Continuous has a difference of 0.74 mV and repetitive has a difference of 1.06 mV. The smallest difference is from 60 to 80 seconds for continuous, with a difference of 0.15 mV. The smallest difference is from 0 to 20 seconds for repetitive, with a difference of 0.83 mV.

Discussion

Results from this experiment do support the hypothesis that nerve based fatigue will occur quicker than metabolic fatigue. The results show that even though there is a difference, it is not very significant. For this experiment, nerve based fatigue was measured using a repetitive grip force, and metabolic fatigue was measured using a continuous grip force.

Figure 1 shows how on average after 80 seconds, muscle fatigue does occur at a quicker rate when repetitively gripping than when continuously gripping. These differences are not significant for a majority of the subjects. Over time the maximum repetitive grip strength becomes lower than continuous, but not by many Newtons (Question 2). Figure 3 does a better representation of demonstrating how nerve based fatigue occurs at a faster rate. From 60 to 80 seconds, the muscle exerts about the same amount of force for gripping continuously or repetitively. When 80 seconds is reached, this is when the subject had to exert more force and grip the Hand Dynamometer tighter. The amount of grip force exerted in Newtons with continuous grip is almost double the amount exerted with repetitive grip. This shows that when a muscle repeatedly contracts then relaxes, this quickens the rate at which the muscle fatigues.

Figure 4 shows that there was a larger difference between maximum and minimum mV for repetitive grip than for continuous grip. Since the EMG signal detects when an action potential is taking place (Raez et al. 2006), a larger the difference of mV means more action potentials are occurring with repetitive gripping. When more action potentials occur, the muscle contracts more, causing it to exert more energy. This is what causes muscle fatigue to occur. Since repetitive gripping has a larger difference in mV, this supports the hypothesis that nerve based fatigue occurs quicker.