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Chapter 13, 16, 21
MUSCULAR ENDURANCE
Preparation: Ch. 13,16, 21
Whereas muscular strength is a function of the size of the muscle fibers and the number of motor units recruited for the contraction, muscular endurance is determined by the blood supply available to the muscle fibers. By definition, muscular endurance is the ability to maintain either a sustained isometric contraction or repeated isotonic contractions. Endurance in a muscle group ends or fatigue begins when the blood flow is occluded to the point where neither sufficient oxygen can be delivered to the muscle fiber nor metabolites and water effectively removed. Occlusion of the blood flow occurs due to the mechanical pressure of the contracting muscle and to the high intramuscular pressure. A contraction of 70% or more of the maximal voluntary contraction (MVC) results in total occlusion of the blood supply and the inability of the muscle to maintain a contraction. Isotonic tests of muscular endurance typically include the 1:00 sit-up and 1:00 bench press test. For isometric measurements the handgrip dynamometer is used.
Application
Success in aerobic activities is primarily dependent upon the blood supply available to repeatedly contracting muscle fibers. The blood supply surrounding muscle fibers is referred to as the capillary density. Capillary density is greater around large fibers and around those with more mitochondria (red, slow twitch fiber).
In adhering to specificity in training for endurance athletes it would seem most advantageous to select a workload resistance that would be heavy enough to over load the muscle and cause hypertrophy of the fibers and be of sufficient duration to stimulate the increase in the number of capillaries. A balanced resistance/volume program would have the athlete training in the range of 12RM – 15RM.
Indicated, also, would be the use of heavy resistance (3RM – 5RM) weight training in the off season to develop larger fibers, or strength. Presumably the stronger athlete could endure longer since it would take a larger effort or contraction of more motor units to reach 70% of his MVC, ie.,the point of insufficient blood supply.
Objectives:To understand the differences between muscular strength and muscular endurance.
To understand changes in the muscle due to aerobic training.
To explain reasons for muscle fatigue in individuals of varying strengths using absolute and relative workloads.
Equipment and Supplies
Bench Press or Vertical Press machine
Metronome
Stopwatch
Data Collection
Isotonic contractions – Bench Press or Vertical Press Test
Choose the same two participants (1 male and 1 female) as you used for the 1 RM testing so you will have the data from that lab to compare to absolute muscular endurance. If you conduct this lab with two different participants you will need to perform their 1 RM prior to completing this lab.
1. Set the weightmachine or equipment you used for the 1 RM testing to 35 lbs. for a female participant and 85 lbs. for a male participant.
2. Each participant lifts and lowers the weight in cadence with a metronome set on 60 bpm (30 reps / minute). Meaning that the participant will lower the resistance in 1 second and lift the resistance in 1 second. You can download a free metronome from your phone in the App store.
3. Time to fatigue (until participant fails to keep cadence) is recorded on the data sheet, last page of this lab.
Lab Interpretation
1. Is there a relationship between strength and endurance? Explain in at least a paragraph.
2. If you were to set the chest press or bench press exercise at a relative load of 70% of the participants 1 RM would participants with a greater 1 RM be able to complete more repetitions at this relative load? Please explain in detail.
3. What other factors may account for differences among participants with regard to muscular endurance?
4. Physiologically, how do you explain differences in the ability to endure between weakest and strongest participants when an absolute load is used? Explain in detail.
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