Section 1 – Energy The Energy Continuum / Thresholds

Session Objectives By the end of this session you should be able to: explain the factors that determine how the energy systems combine to provide energy for different sporting activities identify the importance of thresholds explain the term ‘OBLA’

Background Energy when exercising is FUEL for contraction The body has 3 energy pathways that are always operating The primary source of energy is dependent on the intensity, and to a lesser extent the duration of the activity The body will supply energy, continuously (energy continuum) for the entire duration of the activity, and beyond, to repay the oxygen debt incurred (recovery process)

The need for a continuum Some activities fit neatly into the realm of one or other of bodies energy pathways e.g. 100m sprint ATP-PC system

The mix The majority of sports / activities / events require varying proportions of aerobic and anaerobic energy production

The energy continuum explained The ‘energy continuum’ refers to the ability of the body to sustain energy production for activities to exceed the limits of one or more energy system or that experience changing levels of intensity throughout the duration At one end of the continuum you would experience events that require 100% aerobic metabolism, and at the other end you would have events that require 100% anaerobic metabolism

Energy continuum applied

Position on the continuum An activities position on the continuum is governed by the intensity of the sport i.e. how quickly the energy needs to be supplied and the duration A good indication of intensity is to look at Heart Rate and calculate a percentage of the performer’s maximum at which they are performing (VO 2 is more accurate)

Where does the 1500m fit in?

Practical application – 1500m The 1500, track race would fall in the mid range of the continuum The beginning and the end of the race requires anaerobic energy production (approx 55% of total energy) with the mid race relying predominately upon aerobic energy production (approx 45% of total energy)

The Science Initially, as exercise begins, ATP’ is consumed directly, then replaced via the ATP—PC anaerobic energy system, as well as glycolysis and aerobic conversion of carbohydrates to provide energy for ATP manufacture.

Thresholds When exercising you will either be in the “Zone” of one of the energy pathways / systems or you will be in the “Threshold” between two of the of energy pathways / systems. When reaching a threshold a particular energy pathway is no longer able to sustain energy production at the level required and an additional energy pathway will begin to play a more significant role.

Energy System Thresholds

The transition between energy systems Consider the following: If exercise is intense enough, active cells rapidly run out of PC, so the replacement ATP-PC mechanism stops as the alactic-lactic threshold is reached

Threshold Change: PC →Lactic Acid 1.Stored ATP is used up during the initial contractions. 2.After stored ATP has been used up ADP reacts with PC to recreate ATP. This is the PC Energy system and will provide energy for up to 10 seconds. 3.As the PC begins to run out another energy supply needs to be found. The body begins to use the Lactic Acid System to make up the shortfall of energy to enable contractions to continue at a similar intensity. 4.As the PC stores become depleted the intensity level will drop off slightly and this will enable the Lactic Acid System to provide the majority of the energy.

Which energy system? Whilst intensity is a key factor in which energy system is being used, other factors include: Supply of oxygen – and whether we can avoid OBLA Activation of various enzymes and food fuels being used (see chart)

Activators for Energy Systems Energy SystemControlling Enzymes Activator PC systemCreatine kinaseIncrease in ADP Lactic Acid system Phosphofructo- kinase Decrease in PC Aerobic SystemPhosphofructo- kinase Increase in adrenalin / decrease in insulin levels

OBLA There becomes a point where the aerobic system cannot supply the energy quickly enough and the body has to switch to anaerobic processes This is known as the ‘onset of blood lactic acid’ (oxygen debt)

Measurement of Blood Lactic Acid Measuring blood lactic acid is an indicator of OBLA Normal values are between 1-2mmol per litre of blood Once value reaches 4mmol, OBLA has been reached

Factors affecting OBLA The onset of OBLA depends largely on the fitness of an individual Untrained individuals reach OBLA at around 50% VO 2 max Highly trained athletes reach OBLA at around 85% VO 2 max

Effects of OBLA Lactic acid levels rise Drop in pH of blood Inhibits enzyme action Leads to muscular fatigue Has negative effect in performance