Emily WeimerLaboratory #6: Muscle Strength, Endurance, & FatigueIntroduction:The focus of this lab was to analyze the relationships between muscle strength, force, endurance and fatigue. These variables were studied while engaging in isometric exercises. Muscular strength is directly related to the cross sectional area of the muscle. Thus, having larger muscles will result in more muscular strength, and ultimately producing more force. When studying muscular strength in an individual, it is also to note that training status, gender, age, genetics, illness, and injury play roles in influencing strength. Increasing muscular force can be done through resistance training. Resistance training results in an increase in sarcomeres, which results in greater force generation from the muscles. Muscular endurance refers to the ability of a muscle or muscle group to sustain a force for a prolonged period of time. Muscular strength looks at how much force, whereas muscular endurance looks at how long. Muscular fatigue happens at the end of muscular endurance, referring to the decline in maximal force production during both short-term, high-intensity exercise or long-term submaximal exercise.The muscular contractions that happen in the body allow for exercise to take place. Thesecontractions are the generator of muscular force. They are dependent on the number of attached cross bridges and the regulation of actin and myosin across these bridges. These contractions are also based on the rate at which they are recruited, the number of motor units recruited, and the size of the muscle. In order for motor units to fire, they require action potentials. Action potentialswork in an “all-or-nothing” fashion, meaning that if the action potential is weak, the motor unit will not fire at all. When performing an easy task, fewer motor units will be recruited than if the task was more difficult. When firing motor units, smaller units are first activated, followed by larger motor units if necessary to produce a greater force. Lastly, rate coding also influences muscular force. This refers to how many action potentials can be sent down the motor unit per second. Fast fibers usually have faster rate coding than slow fibers, meaning that more action potentials are sent down per second. Fatigue happens as a result of a slowed activation rate. Slow fibers have a high number of mitochondria, which allows them to maintain maximal force longer, making them highly resistant to fatigue. Maximal force is reached when two forces add up, or summate, as a result of two activations following each other very closely in time.Muscular fatigue happens as a response to exercise, dependent on the type and mode of contraction, resulting in a reduced physiological ability to contract. Fatigue can either be centrallyor peripherally located. Central fatigue happens when there is a reduction in the number of functioning motor units or a reduction in motor unit firing rate. Peripheral fatigue happens when there is an inhabitation of excitation contraction coupling, resulting in the release of calcium and formation of cross bridges. During this lab, an electromyography (EMG) was used to measure muscular strength, muscular endurance, fatigue, and recovery. The maximal voluntary contraction (MVC) was used to indicate muscular strength. As the participant hits their maximal force, there is a decrease in the firing rates of the motor units, leading to fatigue. To see the relationship between multiple intense contractions and decreases in force, participants also participated in a muscular fatigue and recovery test. Methods:Using the BioPac computer program for data recording, all lab students will be asked to use the handgrip dynamometer. Each participant will produce three different MVC recordings. With elbow placed on the table, participant must clench handgrip dynamometer, for approximately three seconds. This process should then be repeated three times. MVC should be recorded after three force productions. For the fatigue recovery test, the participant in each group that produced the lowest MVCwill be used. This test involves the participant conducting twelve, ten-second contractions with maximal effort. During each the ten-second period, the participant will contract for seven secondsfollowed by relaxing for three seconds. After all twelve of these contraction/relaxation phases, theparticipant will conduct five MVC’s, each lasting approximately three seconds, as previously done in the first part of the lab. Following the twelfth contraction, the MVC’s will be done at 30, 60, 120, and 240 seconds. The two highest MVC’s (two male, two female) will then participant in the muscular endurance test. EMG pads will be placed on their dominant arm, one on the distal part of the radius, one on the proximal part of the ulna, and one on the back of the elbow. White, red, and black cords will be attached to these EMG pads, respectively. Based on each participant’s MVC, the BioPac program scale will be at 5% of their MVC, and midpoint at 30% of their MVC. Before test begins, participant should practicing maintaining 30% of their MVC. The test ends when the participant drops to 25% of their MVC.Results:Table 1. Recovery from Fatigue:PeakBaseline(N)Post MVC(N)30s 60s 120s 240sForce 242.41 153.62 152.08 186.98 189.72 217.09Fatigue index .634 .627 .771 .783 .896Table 2. Peak Force ResultsNameMax MVC(N)Forearm Circumference(cm)Mirra 299.55 22.5 Emily 245.49 24.4 Shayan 442.22 28.8 Kylie 242.41 23.5Jeana 307.59 25.5Liz 216.41 24.3 Ashley 208.05 24.1Zoe 373.00 28.5Jill 259.35 22.9Natalie 248.57 25.6Bekah 348.12 24.9Rae 319.7 27.7Hargon 292.7 23.4Anna 251.6 24.6Mikayla 220.4 24.3Shayan 442.22 28.8Brandon 474.2 29.8Ian 572.78 29.8Alec 435 27Seigen 498 28.5Adrian 442 28Table 3: Endurance ResultsName Training StatusMaxMVC(N)Time toFailure(s)InitialEMG(mV)FinalEMG(mV)Zoe Division 1 athlete, rowing 373.00 140 1.158 3.6Bekah Gym 1-2x/week 348.12 252.12 1.7 5.04Ian Occasional gym, ~3x/week, but takes afew weeks off572.78 119.32 4.06 9.99SeigenDance 5x/week 498 243 1.9 9.222.5 23.5 24.5 25.5 26.5 27.5 28.5 29.5 30.50100200300400500600Peak Force vs. Forearm CircumferenceForearm Circumference (cm)Max MVC (N)Discussion: During the fatigue test, force measurements were much lower than the previous MVC measurements. Our participant’s MVC was originally 242.41 N, and decreased to 153.62 N immediately following the fatigue test, the force stayed