Emily Weimer Laboratory 6 Muscle Strength Endurance Fatigue Introduction 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 These contractions 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 potentials work 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 centrally or 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 MVC will 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 seconds followed by relaxing for three seconds After all twelve of these contraction relaxation phases the participant 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 Peak Post MVC Baseline N N Force 242 41 153 62 Fatigue index 634 Table 2 Peak Force Results Max MVC Name N Mirra 299 55 Emily 245 49 Shayan 442 22 Kylie 242 41 Jeana 307 59 Liz 216 41 Ashley 208 05 Zoe 373 00 Jill 259 35 Natalie 248 57 Bekah 348 12 Rae 319 7 Hargon 292 7 Anna 251 6 Mikayla 220 4 Shayan 442 22 Brandon 474 2 Ian 572 78 Alec 435 Seigen 498 Adrian 442 30s 60s 120s 240s 152 08 627 186 98 771 189 72 783 217 09 896 Forearm Circumference cm 22 5 24 4 28 8 23 5 25 5 24 3 24 1 28 5 22 9 25 6 24 9 27 7 23 4 24 6 24 3 28 8 29 8 29 8 27 28 5 28 Table 3 Endurance Results Name Training Status Zoe Bekah Ian Division 1 athlete rowing Gym 1 2x week Occasional gym 3x week but takes a few weeks off Dance 5x week Seige n Max MVC N 373 00 348 12 572 78 Time to Failure s 140 252 12 119 32 Initial EMG mV 1 158 1 7 4 06 Final EMG mV 3 6 5 04 9 99 498 243 1 9 9 2 Peak Force vs Forearm Circumference 600 Max MVC N 500 400 300 200 100 0 22 5 23 5 24 5 25 5 26 5 27 5 28 5 29 5 30 5 Forearm Circumference cm 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 about the same 30 seconds post test as well At 60 seconds post test force increased from 152 08 N to 186 98 N