Chapter 22 - Muscular and Circulatory Endurance Endurance is defined as the ability to resist fatigue endurance is probably the single most important factor in both athletics and physical fitness few sports do not require endurance, so much of training is improving endurance Endurance can be examined both locally (peripherally) and generally (central) Local Endurance appears related to 3 things: Strength of the muscle group Energy Stores Peripheral circulatory factors Central Endurance appears more complex, and is related to: Strength of the muscle group Energy Stores Systemic Circulatory factors - Aerobic ability (VO2, VE, Q, etc.) - Anaerobic ability (glycogen, atp/cp, pH buffers, etc.) Heat Dissipation Neural Control Local Endurance Simplest example - Isometric Contraction @ 60% MVC, virtually complete occlusion of the blood flow occurs therefore, contraction is limited to muscular factors atp/cp stored, rate of energy depletion, pH buffers, etc. it's believed that drop in pH causes fatigue in this muscle low pH reduces the binding of Ca++ with troponin, contraction inhibited therefore, isometric endurance decreases with the intensity (% MVC) refers to relative endurance (% MVC) relative endurance not related to strength absolute endurance is related to strength occlusion of blood flow is not constant with each muscle occurs at different % of MVC depends upon fiber orientation Recovery from maximal exertion occurs fast (about 10 minutes) differs between individuals depending upon the specificity of training the closer the fatiguing activity is to training, the faster recovery time is Factors affecting Muscular Endurance Age has relatively little effect Gender also has little effect Temperature heating decreases endurance cooling increases endurance (until 80 degree temperature - considered optimal) Cross - Educational effect training one limb also increases endurance in the other 10x increase in one resulted in a 3x increase in the other Circulation peripheral vascularization (capillaries) increases, so circulation increases probably the most important factor Training to improve Muscular Endurance Landmark study - 1956 - Hellebrandt and Houtz over 600 subjects used intermittent exercise bouts of 30 seconds on and 30 seconds rest performed sets of 25 contractions manipulated the workload by adjusting the resistance work curves plotted, optimal load determined subsequent days resulted in overloads for some subjects and underloads for others overloads resulted in substantial gains in strength, power, and endurance underloads did not since volume of work was much greater with the high resistance, comparisons were also made at equal volumes findings were conclusive - only overload training resulted in increased endurance Similar Research - Clarke and Stull Comparison made between low resistance - high repetition and high resistance - low rep endurance type vs. strength type training each produced comparable gains for strength and absolute endurance relative endurance was unchanged (this is what was desired to be improved) study replicated at least two times Conclusion: before beginning endurance training, Optimize strength General Endurance Activity involves more than just a few muscles / joints Body moves using a large percentage of musculature (running, cycling, etc.) Central factors are probably limiting factors of endurance Explosive actions (a few seconds) - atp/cp system Maximal activities (up to 1 minute) - glycolysis Maximal activities (beyond 1 minute) - increasingly dependent upon VO2 Consequently, VO2max and AT are the best predictors of performance Fatigue Theories Energy Substrate At exhaustion on a bicycle, muscle glycogen is depleted As cycling is dependent upon thigh muscles, is glycogen depleted by running? Answer is NO, so energy substrate is probably not the reason - Even cyclists can continue beyond fatigue by reducing intensity - FFA's allow workload to be reduced to only 60-70% max Genetic Factors Ultimately set the physiological "ceiling" for training improvements Should not be considered unless dealing with world-class athletes Motivation is almost always a much bigger factor VO2max Probably the single most important factor - except in events of several hours (glycogen depletion) Very high correlation's between race times and VO2 max Also, very high correlation's between AT and Marathon times. Why ??? Results of training Lower resting HR Lower HR at a given workload Greater Qmax Greater SV Lower VE (less Ve at a given VO2) Greater VO2max Greater O2 debt capacity Faster recovery time Training for Distance Events Involves 3 principles (should be familiar by now) 1. Identify what the goals of the program - then determine which training program best meets those goals 2. Place early season emphasis on weaknesses - concentrate on strengths during the latter phase of training 3. Use effective long range planning to reach goals - gradual increases in intensity and duration - prudent (yet ample) use of rest and recovery days Types of training LSD (long slow distance) purpose is to develop the cardiorespiratory system the circulatory system the muscles metabolic potential (mitochondria, etc.) intensity is low (65-75% of max) duration is long (1-2 hours) most appropriate at the beginning of a cycle Use of AT Knowledge of AT and training around it produce huge benefits Training below the AT maintains VO2 and endurance Proper training above AT increases VO2 Interval Training and AT Is difficult to maintain exercise above AT, so use Intervals short periods of work with short rest periods Can perform much more work than continuous Amount of work depends upon three factors Intensity of exercise Duration of exercise interval Duration of recovery interval These three factors can be manipulated to change the workload Best training effect: Higher intensity exercises w/ shorter intervals - both exercise / recovery Ideal is 30 second intervals of near maximal exercise However, athletes peak in 4-6 weeks of this Then, need to change workout - Follow periodization plan Marathon Training Goal is to increase AT Follow periodization of LSD and IT (Interval training) Progress from longer (5 mile) to shorter (1/4 mile) intervals Also should use some carbohydrate loading to store glycogen fully - Big bounce effect - The bigger the depletion, the bigger the storage