Anaerobic Sprint Efforts

Anaerobic/High-Intensity "Sprint" Efforts

• Common in many sports, involving maximal energy release (mostly anaerobic) for 2-60s
• Important for sports performances, including straight-line speed, changing pace, and the "flying finish"
• The rate and capacity of energy supply are essential

Energy System Review

• ATP+PCr system predominates during very short, high-intensity efforts (<5s)
• The glycolytic system predominates during short, high-intensity efforts (5s - 1 or 2 min)
• The oxidative system predominates during extended high-intensity efforts (1 or 2 min - 1 or 2 h) with glycogen stores as primary fuel
• The oxidative system predominates during endurance exercise efforts (> 1-2h) with fats as primary fuel as glycogen diminishes

Energy Supply During Sprints

• Single, short sprints mainly use ATP+PCr and anaerobic glycolytic systems
• Prolonged or repeated sprints need significant aerobic input

Outcomes of Anaerobic Sprint Efforts

• PCr falls as it supplies energy to resynthesize ATP
• Anaerobic glycolysis stimulates energy supply
• Lactate & H+ are produced, decreasing pH
• The anaerobic glycolytic system begins to fatigue, tapping into aerobic sources, which slows the rate of supply
• The aerobic system is predominant by ~75s

Goals of Anaerobic Training

• Increase the rate of energy supply
• Increase the capacity of anaerobic systems to supply energy
• For efforts with more aerobic contribution, increase aerobic energy supply rate

Measuring Anaerobic Performance

• Unlike aerobic fitness (VO2max), there's no standard test for anaerobic systems
• Common tests include the Wingate test, maximal accumulated oxygen deficit (MAOD), and sport-specific time-trials/simulations (assessing CP and W')

Training Anaerobic Energy Systems

• Anaerobic training is exercise above VO2max, stimulating anaerobic energy production
• Adaptations are specific to the training and muscles used
• Aim to improve rate and capacity of energy supply
• Uses high-intensity intervals (HIT or HIIT)
• High-intensity/maximal training is needed, matching event intensities by dividing sprints into intervals to allow more work

Simplifying Anaerobic Training Sessions

• Sessions split into those being <10s, and those between 10-60s
• Repeated short sprints (<10s)
• Repeated prolonged sprints (10-60s)
• Sometimes called speed and speed endurance

Energetics of Repeated Efforts

• Insufficient recovery between efforts builds up fatiguing metabolites like H+ and causes insufficient recovery of energy systems like PCr and lactate
• Short sprints with minimal recovery or prolonged sprints with short recovery increases the contribution of oxidative supply systems and limits work rate

Adaptations to Anaerobic Training

• Adaptations are more debated than aerobic training and difficult to study
• Adaptations are generally peripheral, affected by exercise length, rest time, work:rest ratio, and time between sessions
• Two categories of adaptations occur including metabolic and muscular

Metabolic Adaptations

• Metabolic changes occur in trained muscles, increasing the capacity to produce energy
• This could be due to enzyme increases, enhanced fuel storage, and improved accumulation control of fatiguing metabolites

ATP + PCr Energy System

• Short, maximal sprints rely on energy from PCr
• Elite sprinters deplete PCr stores rapidly, but ATP concentration is buffered by energy systems, preventing drastic drops
• Running out of ATP would be catastrophic

ATP + PCr Energy System - Creatine Kinase

• Short sprint training may increase creatine kinase (CK) activity, which could allow faster PCr breakdown to resynthesize ATP, though studies disagree
• Prolonged sprint training relies more on glycolytic/aerobic energy as it doesn't allow PCr recovery
• Overall, CK likely doesn't play a large part due to inconsistent results

ATP+PCr Energy System - Myokinase

• ADP levels rise rapidly as energy is used
• Short sprint training may increase myokinase (MK, adenylate kinase) activity
• Prolonged sprint training may develop similar adaptations with sufficient rest, enhancing ATP resynthesis
• Several days between training stimuli may improve response

Adaptations Within the Glycolytic System

• Glycolysis rapidly supplies energy at the start of high-intensity anaerobic exercise
• Peak supply rate within ~5s and can be maintained for several seconds
• Powerful energy supply, predominant for 1-2 minutes (~75s of maximal exercise) like a 400m run or 100-200m swim
• The side effect is lactate and H+ accumulation, leading to anaerobic glycolysis

Anaerobic Glycolytic System - Phosphorylase

• Phosphorylase (PHOS) converts glycogen to glucose 6-phosphate for glycolysis
• PHOS activity increases, increasing glycogen breakdown for glycolysis
• PHOS is increased with prolonged or short sprint training

Anaerobic Glycolytic System - PFK

• Phosphofructokinase (PFK) is a rate-limiting enzyme in glycolysis
• Its activity increases after prolonged sprint training or a combination of long and short sprints
• Short sprint training has a slight effect, needing greater stimulation of glycolysis

Anaerobic Glycolytic System - LDH

• Lactate dehydrogenase (LDH) converts pyruvate to lactate
• Pyruvate and lactate are a store for H+ so that glycolysis can continue rapidly
• Increasing LDH activity allows glycolysis to continue faster and longer
• LDH tends to increase with prolonged or short sprint training

Glycolytic Enzyme Changes - Summary

• Increased glycolytic enzymes lead to increased rate and duration of energy supply, improving short, high-intensity exercise

Adaptations Within the Aerobic System

• ATP+PCr and anaerobic glycolytic systems have limited capacity
• Prolonged sprints need aerobic energy
• Repeated efforts with limited recovery increase aerobic supply, restricting the rate of supply

Aerobic Energy System

• Training prolonged sprints or repeated sprints with minimal rest stimulates the aerobic system and is likely to cause adaptations in previously untrained participants
• SDH, CS, and VO2max may increase
• Introducing these efforts into endurance programs may improve high-intensity function without hindering aerobic adaptations

Aerobic Energy System

• Higher aerobic fitness increases PCr recovery rate between efforts, requiring O2, and HLa- clearance, which improves training quality for repeated sprints, e.g. in team sports

Changes in Resting Metabolites - ATP + PCr

• ATP+PCr stores are largely unchanged post anaerobic training, ATP stores may diminish following high volume/intensity training
• Heavy training may decrease ATP:ADP
• Leads to increased adenylate kinase reaction to supply energy
• 2 ADP are converted by myokinase/adenylate kinase into ATP + AMP, leading to an increase in myoadenylate deaminase reaction converting AMP to IMP + NH3, resulting in loss of purine bases needed to resynthesize ATP

Changes in Resting Metabolites - Glycogen

• Storing more glycogen in muscles might allow faster access and greater capacity for glycolysis
• Studies on the effect of anaerobic training on increased glycogen stores have been mixed, and it is difficult to control CHO intake during the study

pH Buffering

• High-intensity exercise using anaerobic glycolysis leads to increased lactate + H+, which results in decreased pH and causes fatigue
• Blood pH can drop as low as 6.9 after intense anaerobic efforts

pH Buffering

• Results are mixed, but typically, training increases monocarboxylate transporters (MCT)
• Usually, max HLa- is higher, which is representative of better clearance and slows the rate of accumulation within the muscle
• Improvements in capillarization, if the aerobic system is also stimulated, may improve metabolite transfer

Muscular Adaptations

• Muscle is highly trainable and will respond to anaerobic training
• General changes include changes in fiber types
• Changes in fiber size
• Changes in sarcoplasmic reticulum

Changes to Fiber Types

• Sprint trained athletes have a higher proportion of type II fibers in their exercising muscles
• Type II fibers are more powerful and relax more quickly
• Genetics plays a part, 50/50 genetics/environment
• Anaerobic training generally leads to increased type II fibers (IIA and IIX combined)

Recovery Times Between Sprints

• Shorter sprints and adequate recovery lead to better type II development
• Prolonged/repeated sprints with short recovery reduce type II development and lead to some type I development due to increased aerobic input and fatiguing of type II fibers

Recovery Times Between Sessions

• Frequency of training and recovery time between sessions can be significant
• Less frequent sessions favor type II fibers, while more frequent sessions favor type I

Changes in Muscle Fiber Size:

• Type II fiber cross-sectional area will increase
• Type I may also increase in cross-sectional area
• Short-term training is less effective
• A minimum of 6 weeks to several months is necessary
• Power:weight is more important than cross-sectional area alone

Sarcoplasmic Reticulum (SR) Development

• Type II fibers have double the terminal cisternae volume and area of type I fibers, resulting in quicker Ca2+ reuptake
• Type II fibers have 5-7x greater Ca2+-ATPase enzyme density = an ability to fluctuate force levels
• Ca2+-ATPase transports Ca2+ to and from the SR
• SR volume might increase post anaerobic training