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6. Muscle Damage.docx

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Kinesiology 2230A/B
Glen Belfry

Lecture 6 Sprinting It is in this phase just before the foot strikes the ground that the hamstrings, most commonly the biceps femoris muscle, are injured. The muscles are maximally activated and are approaching their maximum length There is extension of leg over a relatively short angle of hip 1. During sprinting, the hamstring muscles work eccentrically to decelerate the tibia as it swings out. The hamstrings are going from complete shortening… 2. to a lengthening situation very quickly 3. the leg is at full extension, the hip is starting to extend At the last stage, the hamstrings are at their greatest length as well as instantly maximally activated. This is a huge lengthening contraction (lengthening = actin myosin bridges broken). • It is in this phase just before the foot strikes the ground that the hamstrings, most commonly the biceps femoris muscle, are injured. • It usually occurs past 30 meters down the course because metabolically you are switching from ATP-PCr to a slower glycolysis, meaning energy will be produced at a slower rate.  energy that the muscle requires to contract AND relax is going to take longer, therefore the cross bridges will not break as fast. Remember that relaxation is slower than contraction  where injury will occur Recall: Muscle Spindles Muscle spindles are located regularly throughout muscle. They monitor information on the change of muscle length (position) and rate of change. Any change in length of the muscle is either going to generate greater tension on central area (lengthening) or less tension (contraction/shortening). • At rest there is a particular nervous frequency (10 Hz). As the muscle lengthens, the frequency becomes faster. • As soon as there is no tension, you are unable to change frequency. So, as the muscle shortens the contractile units on either side maintain some tension on the central area to maintain observance of change in tension/length on central area – frequency. Stretch Reflex: time between hitting the patellar tendon and the reflex contraction that ensues. The contraction is initiated by the quick lengthening of the muscle spindle. Golgi Tendon Organs Located at interface of muscle and tendon. Sensitive to tension System of afferent nerves interwoven in cartilaginous tissue. Any force generated will be transmitted to the tendon area and it will monitor the tension. It will give feedback information about force levels in the muscle to the central nervous system. There is also a protective reflex - when put under extreme tension the Golgi tendon organs will cause inhibition of the muscle that has had an extreme load applied (agonist). It will also lead to a contraction of the antagonist. • There is an inhibition of this reflex with training. Muscle Soreness and Recovery Acute muscle soreness: may be pain due to ischemia or accumulation of end products (H+ and H2O) • A drop in pH causes significant pain Delay onset muscle soreness (DOMS): Muscle soreness a few days after over use • Not directly related to lactate build up Muscle Soreness is observed with eccentric (lengthening) vs. concentric (shortening) contractions • During a muscle lengthening you will have disruption of membrane at the anchor points (Z and M line) as well as in the myofibrils themselves • Symptoms include: increased muscle enzymes
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