Victoria NewburyLab Tuesday 1:00Due Date: 4/18/14KIN 470 Exercise PhysiologyGrad TA: Ben HoffmanLab Report 6: Muscle strength, endurance, & fatigueINTRODUCTIONThe important vocabulary terms for the purposes of this lab are as follows. Muscle strength can be defined as the ability of the body to produce force against resistance. Muscle endurance, which can often be paired with muscle strength in terms of ability, is the ability for the muscle to resist fatigue and perform muscular contractions against resistance for multiple sets. Muscle fatigue is the point of time at which the muscle in inability to perform any successive contractions without first resting. Excitation-contraction coupling is when an electrical signal is converted into a mechanical action by the body. The message to contract originates in the brain and is sentto the muscle via the CNS and PNS. The electrical signal becomes chemical in the motor neurons, which create a mechanical contraction. The force of the contraction is dependentupon the message that was sent to the muscles. EMG (electromyography) is a measurement of the electrical activity occurring in a muscle. It is often used for the heart in order to track heart beat via depolarization and polarization. Greater amplitude signifies a greater amount of electrical activity in the muscle via alpha motor neuron Recruitment is a measure of how many motor neurons are activated in a muscle. Motorneurons innervate the muscle fibers in a muscle. Certain muscles have a high innervationsratio to produce more precise movements, such as the eye. Muscles with low innervationsratios are much more adept for producing force, such as the bicep. A greater force will be produced in muscle with high recruitment. Rate coding is the frequency of motor unit activation. This is the speed at which your body can react to a message sent from the brain to contract. Force production is dependent on this variable because a greater rate coding produces more force. The purpose of this experiment was to examine force, fatigue, and endurance among male and female participants. We used the forearm as the primary isolated muscle under study. Females tend to be weaker than males due to a lack of testosterone therefore it is expected that the females will have a lower maximal voluntary contraction (MVC). Itis also expected that individuals who do not train as much will fatigue easier due to a lackof adaptation in the muscle and nervous system. Endurance is associated most with type Imuscle fibers so those who train aerobically will likely do better in the endurance portion of the experiment. METHODSThe first step was to obtain the force capacity of each of the participants in our small group. This was done using the “Muscle Endurance” function on the Biopac program. The participants sat with their elbows resting on the table and used their dominant hand to squeeze the hand-grip dynamometer with as much strength as possible. This produced an isometric contraction in the forearm and is performed for 3-4 seconds. After the data was collected, it was analyzed to find their peak force. The member withthe lowest force capacity proceeded to the fatigue phase of the experiment. The participant with the highest force capacity participated in a competition among the highest scoring participants from the other 5 groups.The fatigue phase of the experiment entailed the participant to perform 12, 7-second contractions with hand-grip dynamometer. Each contraction had 3 seconds of rest following it. This procedure totaled to 120 seconds and was recorded on the Biopac. Immediately following the fatigue phase, the participant participated in the recovery phase of the experiment. During the recovery phase, the participant performed 4 recovery MVC’s with a 3-4 second contraction. There was a contraction immediately after the 12th contraction, 30 seconds after, 60 seconds after, 120 seconds after, and 240 seconds after. This concluded the protocol required for the participant who originally had the lowest force capacity.The participant who has the highest force capacity moved on to perform in the endurance portion of the experiment against the representatives from the five other groups. EMG sticky pads were attached to their dominant arms (distal region of the radius, proximal region of the ulna, back of the elbow). A white cord was attached to the one over the ulna, a red cord to the one over the radius, and black to the one over the elbow. They then performed their MVC and we calculated 5% and 30% of their MVC in order to scale the force measurements to this value. The next step was for each participantto squeeze the hand dynamometer at 30% of his or her MVC for as long as possible. The test ended when they dropped below 25% of their MVC. We then calculated the time theywere able to hold at 30% of their MVC and compared each of the participants.RESULTS Table 1. Recovery from Fatigue: (Me)Peak BaselinePost MVC 30s 60s 120s 240sForce 168.67 89.98 105.2 129.84 168.85 192.11Fatigue index 46.65 37.6 23.02 -.1067 -13.897Forearm circumference: 9.5 cmTable 2. Subject Characteristics Gender Training StatusS1 Male 6x/week resistance & cardioS2 FemaleMostly cardio (biking), some weightsS3 MaleModerate cardio, resistance training 5x/weekS4 Female Hockey 5x/week, weights 2x/weekS5 Male4x/week cardio & weights (more cardio)S6 Female 5x/week cardio & weightsTable 3. Peak Force Results Max MVC Forearm CircumferenceS1 639.6 N 32.4 cmS2 377.2 N 24.6 cmS3 474.89 N 29.3 cmS4 377.7 N 24.8 cmS5 602.52 N 31.5 cmS6 332 N 22.2 cmTable 4. Endurance Results Max MVC Time to Failure Initial FinalEMG EMGS1 639.6 N 216 seconds .7986 mV 2.545 mVS2 377.2 N 360 seconds 1.5 mV 7.1 mVS3 474.89 N 202 seconds .9844 mV 3.217S4 377.7 N 250 seconds .71 mV 2.52 mVS5 602.52 N 103 seconds 1.57 mV 2.97 mVS6 332 N 416 seconds 1.01 mV 3.04 mVCalculations:Fatigue Index = ((peak force-min force/peak force)* 10030 seconds:((168.67-105.2/168.67)* 100 = 37.6DISCUSSIONDuring the fatigue test, the participant’s force production decreased with every succeeding contraction. The reason for this occurring could be because of muscular fatigue. This occurs in response to short-term, high intensity exercise, which the fatigue test would be considered as it required several maximal contractions of the forearm for a little over a minute. This fatigue could have happened due to a number of physiological occurrences in the body such as when there