Inadequate ATP Resynthesis

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1 Indiana Association of Track and Cross Country Coaches Clinic Causes of Fatigue in Sprint Events Chasing Mercury: Training to Combat Fatigue Jason Karp, Ph.D. RunCoachJason.com 2011 IDEA Personal Trainer of the Year inadequate ATP resynthesis via anaerobic metabolism acidosis & accumulation of metabolites creatine phosphate depletion CNS/neuromuscular? Inadequate ATP Resynthesis Improve anaerobic metabolism by increasing glycolytic enzyme activity, muscle buffering capacity, and muscle morphology. Sprint training increases glycolytic enzyme activity. Physically active subjects trained 3 x week for 7 weeks using 30-sec maximum-effort intervals (Wingate tests) on a cycle ergometer. Week 1: 4 x 30 sec w/4:00 rec. Week 2: 6 x 30 sec w/4:00 rec. Week 3: 8 x 30 sec w/4:00 rec. Week 4: 10 x 30 sec w/4:00 rec. Week 5: 10 x 30 sec w/3:30 rec. Week 6: 10 x 30 sec w/3:00 rec. Week 7: 10 x 30 sec w/2:30 rec. Data from MacDougall et al. (1998). *Significantly greater than pre-training (p<0.05). 49% 56% Peak anaerobic power (A) and total work (B) during 4 successive maximum 30-sec Wingate tests w/4:00 recovery. Clear bars indicate pre-training & black bars indicate posttraining values. Data from MacDougall et al. (1998). *Significantly greater than pre-training (p<0.05). Muscle Morphology Fiber Type Type I Type IIA Type IIB Slow-Twitch Fast-Twitch A Fast-Twitch B 1) Change characteristics of each fiber type 2) Change area taken up by fiber type 3) Conversion of fiber types? Increasing % of FT fibers would increase anaerobic power & capacity because FT fibers contain more myosin ATPase & faster rate of release of Ca ++ from SR. We combat fatigue by making muscles act as much like FT fibers as we can by causing 1, 2, &/or Dr. Jason Karp. All rights reserved. 1

2 Muscle Morphology Fiber Type Changes in Muscle Fiber Type Before and After Training Pre-training Post-training % Type I Fibers 45.8 (6.9) 36.2 (4.3)* % Type II Fibers 54.2 (6.9) 63.8 (4.3)* Avg. Diameter Type I ( m) 50.7 (0.8) 52.7 (1.0) Avg. Diameter Type II ( m) 57.9 (2.0) 57.8 (3.8) % Area Type I Fibers 43.0 (6.6) 34.4 (4.0)* % Area Type II Fibers 57.0 (6.6) 65.6 (4.0)* Data from Dawson et al. (1998). *Significantly different from pre-training values (p<0.05). Training consisted of sprint intervals (20-40 x % max speed w/1:6 work:rest ratio, decreasing to 1:4 ratio as training progressed) 3 x week for 6 weeks. Changes in Performances Before and After Training Pre-training Post-training 10-meter time (sec) 1.87 (0.02) 1.81 (0.03) 40-meter time (sec) 5.50 (0.05) 5.37 (0.08)* Supramaximal run (sec) (14 grade until exhaustion) Repeated sprint test time (sec) (6x40m starting every 30 sec) 49.9 (3.5) 55.5 (4.0)* (0.65) (0.49)* Repeated sprint test % decrement 7.1 (2.6) 5.9 (1.2) VO2max (ml/kg/min) 57.0 (2.4) 60.5 (1.9)* Data from Dawson et al. (1998). *Significantly different from pre-training values (p<0.05). Training consisted of sprint intervals (20-40 x % max speed w/1:6 work:rest ratio, decreasing to 1:4 ratio as training progressed) 3 x week for 6 weeks. % Type II fibers significantly correlated with 40m time (r = ) before training. After training, correlation increased (r = ) and 10m time also significantly correlated with % Type II fibers (r = ). ATP synthase adenylate kinase Metabolic Fatigue ADP + P i + H + ADP + ADP ATP + H2O ATP + AMP myosin ATPase stimulates phosphorylase & PFK, increasing glycogenolysis/glycolysis Metabolic Fatigue Inability to resynthesize ATP at required rate to sustain muscle force production limitations in anaerobic metabolism (phosphagen & glycolysis) Acidosis ( H +, ph) dissociation of lactic acid, ATP hydrolysis, glycolytic reactions inhibits Ca ++ release from SR # of cross-bridges & force exerted by each cross-bridge (via inhibition of myosin ATPase) inhibits glycolysis via inhibition of PFK Accumulation of other metabolites Pi inhibits Ca ++ release from SR & inhibits myosin ATPase ADP inhibits cross-bridge detachment extracellular K + & Na + interfere with muscle membrane depolarization & slows propagation of action potential Event-Specific Fatigue 100m/200m: inadequate ATP resynthesis accumulation of metabolites CP depletion CNS?? 400m: inadequate ATP resynthesis inadequate blood flow to/o 2 use by muscles acidosis & accumulation of metabolites CP depletion CNS?? Acidosis/Metabolite Accumulation Workouts that use anaerobic glycolysis as predominant energy system and repeatedly cause acidosis to improve acidosis tolerance, muscle buffering capacity, and anaerobic capacity Dr. Jason Karp. All rights reserved. 2

3 Training Anaerobic Capacity Examples of Workouts Intervals from 45 seconds to ~2 min ( meters) 6 x % of 400m pace w/1:2-3 work:rest ratio 4 x % of 400m pace w/1:3 work:rest ratio Creatine Phosphate Depletion During intense exercise, CP decreases, but is restored within 3-5 min of rest creatine kinase CP + ADP ATP + C H + + HCO3 - H2CO3 CO2 + H2O Creatine Phosphate Depletion Workouts that use phosphagen (ATP-CP) system as predominant energy system to improve anaerobic power. However... Contrary to the increase in muscle glycogen content that results from depleting muscle glycogen by running long distances, research has shown that creatine phosphate doesn t increase in response to its depletion during training. Fatigue is combated by increasing the rate of CP breakdown rather than by increasing CP storage. Examples of Workouts Intervals from 5 to ~15 seconds ( meters) w/ long rest periods to replenish CP & avoid involvement of glycolysis 10 x 50 near max speed w/ 3-5 min passive rest 6 x 150 near max speed w/ 3-5 min passive rest CP + ADP ATP+ C Power Output (W) Influence of Rest Periods sec sprint, 60 sec rest 6-sec sprint, 30-sec rest * * * * * Weight Training & Plyometrics Power = Force x Velocity Heavy weight training targets the force (strength) component of power. Plyometric training targets the velocity (speed) component of power. Reps Data from Holmyard et al. (1988). *Significantly different from 30-second recovery (p<0.05) Dr. Jason Karp. All rights reserved. 3

4 Weight Training & Plyometrics Training Goal Muscular Strength Hypertrophy Neuromuscular Amount of Weight (% 1RM) > 80% > 95% Reps Rest # Sets min 3-5 min Sample Plyometric Program To get the most out of plyometric training, try to spend as little time on the ground as possible between hops/bounds/jumps. Do exercises on a soft surface, such as grass, a track, or a gymnastic mat. Begin with two sessions per week of two sets of ten repetitions (2 x 10) with full recovery between sets. Week Single leg Bleacher Double leg Alternate Squat Depth Box hops hops bound leg bound jumps jumps jumps 1 2 x10 2 x x10 2 x x10 2 x10 2 x10 2 x x10 2 x10 2 x10 2 x10 2 x x10 2 x10 2 x10 2 x10 2 x10 2 x10 2 x x10 2 x10 2 x10 2 x10 2 x10 2 x10 2 x10 Single leg hops: 1) On one leg, hop up and down; 2) hop forward and back; 3) hop side-to-side. Bleacher hops: Standing at the bottom of the bleacher steps on one leg, hop up the steps. Walk back down and hop up again on the other leg. Double leg bound: From a squat position with both legs, jump forward as far as you can. Alternate leg bound: In an exaggerated running motion, bound (which looks like a combination of running and jumping) forward from one leg to the other. Squat jumps: With hands on hips in a squat position, jump straight up as high as you can. Upon landing, lower back into a squat position in one smooth motion, and immediately jump up again. Depth jumps: From a standing position on a one-foot tall box, jump onto the ground and land in a squat position. From this squat position, jump straight up as high as you can. Box jumps: From the ground, jump with two feet onto a box about one foot high, and then immediately jump into the air and back down to the ground. As you get experienced with the exercise, try jumping with one foot at a time. ph P i ADP K + Reduced CNS drive to muscles may result from feedback from muscles metabolic condition or feedforward from neural downregulation or changes in brain neurotransmitters. Force produced by superimposed electrical stimulation is greater than that produced voluntarily (Belanger & McComas, 1981). Subjects can temporarily increase force production when loud verbal encouragement is given (McNair et al., 1996). When isolated fatigued muscle fibers are bathed in solution with caffeine, force production increases (Edman & Lou, 1990; Lännergren & Westerblad, 1991). brain serotonin during prolonged exercise may perception of effort and feelings of tiredness & lethargy (Davis & Bailey,1997; Meeusen et al., 2006). Subjects who trained with 2 legs simultaneously reduced fatigue only during 2-leg task but not during 1-leg task & vice versa, suggesting that CNS command is different for 2-leg tasks compared to 1-leg tasks (Rube & Secher, 1990). Bilateral vs. unilateral training The Brain as the Central Governor After first maximal sprint, signal to cortex or brainstem would indicate that repeating this intensity would damage muscles. Therefore, neural command may be down-regulated & power output consequently declines. Data from St. Clair Gibson et al. (2001). Distance (m) Rep # Session 1 Session 2 Session 3 Session 4 Studies comparing muscle force production & muscle activation level before & after intense running (e.g., 6K at AT; 5 x 300m w/1:00 rest; 10 x max aerobic speed & 18% grade w/2:00 rest) have found: slight MVC force (5-7%) a greater force produced w/electrical stimulation compared to MVC force a statistically significant force produced w/electrical stimulation Non-sig. difference in activation level suggest that fatigue is peripheral, rather than CNS, in nature (Lattier et al., 2004; Škof & Strojnik, 2006a,b) Dr. Jason Karp. All rights reserved. 4

5 Prevailing evidence is that fatigue, at least during short-term exercise, is not caused by CNS but rather by changes occurring in muscle. The CNS seems to play a greater role in fatigue during prolonged exercise. This conclusion is due partly to lack of objective experimental measures of CNS fatigue & less understanding of CNS compared to muscle function. Other Sources of Fatigue Muscle fiber damage repeated sprinting & heavy weight training can cause structural damage to muscles, which results in fewer functioning actin-myosin crossbridges & delayed-onset muscle soreness (DOMS) research has found that muscular force declines during period of DOMS after 24 hrs: 14-50% after 48 hrs: 11-50% (Donnelly et al., 1992; Newham et al., 1987; Talag, 1973; Weber et al., 1994) 2013 Dr. Jason Karp. All rights reserved. 5