Fisiologia de ejercisio

Power, Strength, and Performance:
Harnessing the Musculoskeletal System

Yoshua Seidner

February 15th, 2012

HS342 – Exercise Physiology
Spring 2012

Professor Burgess

Yoshua Seidner
February 15, 2012
Exercise Physiology
Professor Burgess

Lab II – Power, Strength, and Performance:
Harnessing the Musculoskeletal System

Introduction:

The musculoskeletal system iscomprised of muscles and bones and serves the following purposes—support, protection, and ambulation. Even though the various movements performed in this lab require bone function (as do all movements), the focus of this lab will be the role of muscles. Muscles do work and induce movement through contractions (shortening and lengthening of muscle fibers). This is caused in the cellular level by theinteractions between myosin fibers with thinner action fibers. The formation of cross bridges and the pulling action by the myosin “arms” create the force that is seen as a muscle contraction. Contractions can be placed in two broad groups—static or isometric and dynamic. Static contractions are not accompanied with movement around the joint. On the other hand, dynamic contractions involve movementaround one or more joints. More specific groups of contractions include isotonic contractions and isokinetic contractions. Isotonic contractions involve the use of a constant load (as in free weight exercises), while isokinetic contractions involve constant angular rotation around a joint, meaning that the load moves at a constant speed. Apart from the various classifications described above,contractions can either be concentric or eccentric. This further specifies the contraction as either producing a force while shortening (concentric) or producing a force while lengthening (eccentric).
This experiment will involve the measuring of muscle strength through the use of a few techniques. Strength in this case is defined as the maximal force that can be produced by a muscle or muscle group.The most direct of measuring this strength is through the direct 1-RM test, or the one repetition maximum 1-RM test. In this test, progressively heavier weights are lifted, one at a time with rests in between, until a full repetition can no longer be done. This can be very time-consuming and inefficient in which case the indirect 1-RM test can be performed. The indirect version of the 1-RM makesuse of equations that describe the relationship between the percent of 1-RM performed and the number of repetitions. The handgrip test will also be used to give another measure of estimated overall strength. This test measures isometric strength of the forearm flexors.
It is important to note that muscle strength is not directly correlated to muscle power and endurance. Power is known to be moreclosely related to the functional activity being performed as well as muscle fiber type being used. The Wingate anaerobic power test will be used to estimate the muscle power of the subject. Muscle fibers are separated into two main groups, slow twitch and fast twitch. Slow twitch fibers contain a higher percentage of mitochondria as well as an increased level of myoglobin and blood capillaries.This allows for high oxidative capacity (aerobic) and a resistance to fatigue. Because of this, these fibers are used during long-term endurance activities. Fast twitch fibers on the other hand contract rapidly and come in two forms, type IIa and type IIb. Type IIa fibers contain a good amount of mitochondria and myoglobin leading to a medium oxidative capacity and a medium resistance to fatigue.Conversely, type IIb fibers have a low mitochondria and myoglobin composition leading to a low oxidative capacity. These are mostly used for very short-term, very high power activities relying on anaerobic energy pathways.
The purpose of this lab is to measure and analyze the muscle strength and power of an individual through the use 3 techniques: the handgrip test, the indirect 1-RM test, and...