Title: Physiological Determinants of Muscle Endurance
Thesis Supervisor: Dr. Cameron Mitchell
Committee Members: Dr. Robert Boushel, Dr. Martin MacInnis, Dr. Jamie Burr
Chair: Dr. Daniel Gamu
Abstract: Muscle endurance is the ability for a muscle to perform sustained contractions over a length of time against a submaximal load. There is a non-linear negative relationship between contraction intensity and time to task failure such that as the intensity becomes lower the time to task failure rises. There is an inflection point in this relationship where a given decrease in load leads to an exponential rise in performance which is theorized to be the critical occluding tension. The critical occluding tension (COT) is the lowest contraction intensity (or range of intensities) that completely occluded exercising muscle blood perfusion halting oxygen delivery. Exercise at intensities below the COT would then have some perfusion occurring allowing oxygen to get to the working tissues and elongate performance time. It remains unclear if the COT occurs at a similar relative load (i.e., 40% of maximal strength) or absolute load (i.e., 20 kg) for all individuals as there is conflicting evidence in support of both theories. When this perfusion is available those who are better suited for oxygen extraction, such as endurance trained people, should see greater performance than those with a less oxidative muscle phenotype. Further, there is a positive relationship between strength and the pressure generated within a muscle during contraction which suggests that stronger/larger individuals may generate greater pressure during contraction which could lead to differences in when the COT occurs based on strength/size. It remains unclear if participants will generate similar intramuscular pressures when loads are expressed either relative to their maximal strength or matched as absolute loads between individuals, and this unknown relationship may be pertinent in understanding the COT.