Developing Energy Pathways:  Aerobic Energy System

The oxidative system involves four methods to generate ATP:

ü      Slow glycolysis (aerobic glycolysis)

ü      Krebs cycle

ü      Electron transport chain

ü      Beta oxidation

The first method is slow glycolysis.  It comes into play when exercise is sustained for 1-3 minutes.  The break down of glucose consists of a series of enzymatic reactions.  The end result of the enzymatic reactions is ATP.  An individual glucose makes 2 pyruvate molecules and 2 ATP.  Pyruvate molecules enter into the Krebs cycle, but oxygen must be available for this to happen.  Click in this link for a clear understanding of the enzymatic reactions that convert proteins, fats, and carbohydrates into intermediate substances- How the Krebs Cycle Works.  In order for fats to enter the Krebs cycle they must go through a series of enzymatic reactions called beta oxidation.  The reactions condense free fatty acids to acetyl CoA and hydrogen. Acetyl CoA can now enter the Krebs cycle and from this state, fat metabolism continues the same course as carbohydrates.

The next and final step is for the electron transport chain to finish work started by the Krebs cycle.  The electron transport chain makes use of NADH and FADH 2 formed during glycolysis and the Krebs cycle to produce large amounts of ATP.  For a better understanding, click on this link about the Electron Transport Chain: The Movie.

In order for fat cells to enter the Kreb's cycle, the cells must go through a process called Beta oxidation.  The process starts with fatty acids or fat cells, in the form of Acyl-CoA molecules.  These molecules are broken down in mitochondria to make Acetyl-CoA, the entrance molecule for the Kreb's cycle.

Developing Energy Pathways:  Aerobic Energy System

The last energy system I’m going to discuss is the Aerobic Energy System.  When physical activity lasts longer than 2 minutes, the body begins to utilize the aerobic energy system.  This energy system consumes proteins, fats, and carbohydrate (glycogen) in order to make ATP. Development of an aerobic energy system must include various training intensities that improve the aerobic zone or target heart rate zone, which is listed as a percentage (60%- 80%) of maximum heart rate.  Energy efficient/recovery zone intensity is between 60%- 70%.  Training inside this zone improves general endurance and aerobic power.  The aerobic zone is 70- 80%, which helps advance the cardiovascular system.

Use the following as a guide for determining your intensity level:

Novice or low fitness level: 50% to 60%

Intermediate or average fitness level: 60% to 70%

Advanced or high fitness level: 75% to 80%

How to figure out your Aerobic Zone:

The easiest way to estimate your target heart rate is to use the maximal heart rate formula. Keep in mind, this formula does not take into consideration fitness level, medical conditions, or environmental factors that might affect your heart rate. Calculate your Max Heart Rate: (MHR = 220-age)

Target Heart Rate:  MHR x intensity level (from above) = THR

Example: 

220 - 32 years= 188 MHR (the fastest your heart can beat)

188 x .60= 112.8 beats per minute for intermediate fitness level

 Next blog will explain the break down of the Aerobic Energy System.

Developing Energy Pathways:  Anaerobic Lactate Energy System

The next energy system for discussion is the Anaerobic Lactate (Glycolytic) Energy System.  When the ATP-CP energy system is depleted the bodies’ only alternative is to use the stored glucose for ATP.  When glucose is broken down through anaerobic conditions, energy is produced. The breakdown of glucose produces pyruvic acid and hydronium ions.  Since oxygen is not available pyruvic acid is converted into lactic acid.  In the past, lactate or lactic acid was thought to be the cause muscle fatigue and soreness along with delayed nerve response in muscles.  However, we now understand the buildup of hydronium ions (H+) to be the cause muscle fatigue and soreness.  Researchers currently recognize lactate as a very dynamic substance. It is a key source of energy for many physical activities, it is formed by only one energy system (anaerobic lactate energy system), and will be utilized by a further energy system (aerobic energy system) in a different part of the body.  

Process of Anaerobic Lactate Energy System:

-         CP stores are depleted

-         Stored glucose is used as fuel in the absence of oxygen

-         Rapid glucose breaks down to form pyruvate acid molecules and hydronium ions

-         If oxygen is present, pyruvate acid molecules enter the mitochondrion to go through
oxidation (aerobic/ slow glycolysis) or if there is a lack of oxygen the pyruvic molecules are converted into lactic acid (anaerobic/ fast glycolysis)

-         The concentration of hydronium ions only increases if there is insufficient oxygen to the active muscles.  When this occurs the environment becomes very acidic causing muscle fatigue and soreness. 

-          During anaerobic glycolysis, the formation of 4 ATP is produced from 1 molecule of glucose.  2 ATP are used in the process, resulting in only 2 ATP molecules of energy from the process of glycolysis

The chart below provides a breakdown of how to develop your anaerobic lactate energy system.  This energy system requires high intensity and short recovery time.  

Developing Energy Pathways 

As we already know, energy pathways develop in different ways with some overlapping between them. Time and intensity are two key words in this discussion, which define the energy pathways in utilization. The charts below will give you examples on how to increase your upper and lower body explosive power by efficient utilization of this energy pathway.  Let’s talk about the football position called the running back.  Running backs are generally the fastest players on the offensive team. Their position requires them to sprint at a high intensity for a very short period of time.  For a running back to get better they must challenge their Anaerobic Adenosine Triphosphate – Creatine Phoshate (ATP-CP) Energy System and Anaerobic Lactate (Glycolytic) System. 

Process of ATP-CP energy system:

-         ATP can be stored in the muscle for 2 seconds

-         After the 2 seconds is used up, re-building of ATP from CP will last until CP stores are empty (4-6 seconds)

-         There is approximately 5-10 seconds of ATP production

-         For the body to continue using the ATP-CP energy system, there must be an adequate recovery time for CP stores to return to normal.  The longer the recovery time the greater the peak power output recovery (PPO).  Recovery time range is 15 seconds to 3 minutes.

One of the goals in a strength and conditioning program is to introduce and develop training methods that will improve the body’s ability to utilize all energy pathways.  A thorough training program with variation allows the body to become accustomed to the various energy sources.  The next blog entry will discuss the Anaerobic Lactate (Glycolytic) Energy System.

Table adapted from Fox E. L. et al, The Physiological Basis for Exercise and Sport, 1993

ATP- (Adenosine triphosphate) is the energy molecule of all living cells. Humans get energy from food; this energy must be converted to ATP before it can be used by the cells to carry out all necessary functions.  ATP is stored in the muscles and blood.

CP- (Creatine Phosphate): a chemical compound stored in muscle, which when broken down helps in the production of ATP. ADP and CP together produce ATP.

Muscle glycogen- is the main fuel during heavy and prolonged exercise and is only available in the muscle that stores it. Fatigue is linked with muscle glycogen depletion, even when fatty acids are available for fuel.

Lactic acid- provides fuels for many tissues in the body.  Lactic acid is formed during the breakdown of glucose to be used as energy when oxygen is low. The lactic acid system provides energy for high intensity activities lasting up to two or three minutes.

Fatty acids- are a major source of energy production at any time, except after a carbohydrate enriched meal, and they are the main nutrient utilized from fat stores in extended exercise (activity longer than 4 min).

When an athlete designs their strength and conditioning program it is necessary for the program to focus on development of their energy systems and sport specific skills.  Why is this important?  The development of your energy systems will have your muscles, nervous system, and hormones acting together in order to help your body work as efficiently as possible. When you learn a new skill the central nervous system will store the learned motor pattern for the future.  Each time you perform an exercise or a skill, the neuromuscular system continues to develop and build upon the previous experience. Frequent practice of sport specific exercises will create more neuro pathways which are essential for an athlete’s progression.  George Liset says in the article on sensory motor learning that “as an athlete begins to refine a skill, the information is fed back and forth between the brain and the senses until a successful and coordinated pattern of action is formed. This development may be accelerated by stimulation and may be slowed by injury or lack of stimulation. There is an orderly progression in the development of these abilities. Unnecessary and counterproductive muscular movement in the body is detected and weeded out. The movement gradually becomes more refined and efficient over time. Information is exchanged.”

Strength and conditioning principles, along with the terminology, can be really confusing.  For example, what is the difference between functional exercise and sport-specific exercise?  Sounds like the same thing, right?  Well, in certain aspects they are similar and in other aspects they are not. 

Functional exercise is connected to both everyday physical activity and sport specific exercise.  Examples of functional exercises, like everyday physical activity, are reaching in a cupboard or walking up and down a flight of stairs.  To get better at these daily movements, functional strength training is a must.  Functional equipment can include dumbbells, resistance bands, exercise balls, and medicine balls.   

The focus of sport-specific exercise is on the conditioning, strengthening, and skill component for the particular sport.  Remember that functional and sport-specific exercises do have the same purpose which is to restore balance, strengthen, lengthen, improve the neuromuscular relationship, and coordinate movement patterns specific to the particular sport, household, or recreational activities.   With that said, an athlete must plan a training program with the thought of how to meet the needs of their specific sport and this is where the SAID principle comes into the picture. 

 The SAID principle stands for Specific Adaptation to Imposed Demands.  In other words, the SAID principle describes how various exercises or training programs, targeted for a specific activity, can generate changes only in the muscles, soft-tissues, and energy systems stressed by the activity.  (The body has two main energy systems: aerobic and anaerobic energy systems.)  Remember, energy is needed for growth, repairs, and everyday physical activities.  The intensity and duration of the activity will change the amount of energy required for the body’s performance.

 Continuation of article next week.

Strengthening should transition from basic exercises to sport-specific exercises that are intended to replicate movements and skills common in your chosen sport.  Adjusting your strength training to be similar to sport movements will allow for a greater chance of positive transfer to that sport.  Sport-specific exercises are based on the principles of functional exercises.  Functional exercises are defined as exercises involving smooth rhythmic motions in all planes of motion.  The purposes of these exercises are to restore balance, strengthen, lengthen, improve neuromuscular relationship, and coordinate movement patterns specific to the particular sport. 

Now that your physical fitness analysis is complete you can use your results to build your strength and conditioning program.  Completion of the physical fitness analysis allows you to structure your training program to improve muscle deficiencies, maintain strengths, or enhance sport specific neuro-muscular activation.  Keep in mind, athletes will not improve with just weight lifting alone.  Athletes require sport specific resistance training, such as, explosive power, muscular endurance, maximal strength or some combination of all three in order to excel. 

When selecting exercises understanding the exercise type is important.  Exercise type is classified as either core exercises or assistance exercises.  Core exercises involve large muscles.  Core exercises are chosen first because they have a direct effect on improving sport performance.  Assistance exercises isolate smaller muscles and are considered less important to overall improvement of sport performance.  However, the regular use of assistance exercises is for injury prevention and rehabilitation.  Incorporating both core and assistance exercises into your program is extremely valuable in order to improve performance. 

Examples of Core exercises:  bench press (chest), squat (thighs), shoulder press (shoulders), dead lift (hip and thigh)

Examples of Assistance exercises:  abdominal crunch (abdomen), seat row (upper back), lateral shoulder raise (shoulders)

Muscle balance

Keeping muscle properly balanced is another vital component to injury prevention.  The larger muscle groups work together in pairs called agonist and antagonists and those muscle pairs need to be balanced in terms of strength and flexibility.  Agonist is the muscle responsible for contracting during movement.  The antagonist does the opposite, allowing the muscle to relax and stretch.    For example, we bend our knee by using the hamstring muscles.  It's pair is the quadriceps muscle.  The quadriceps muscle must be willing to stretch for the hamstrings to contract and bend the knee fully.

Agonist & Antagonist Pairs

Sport specific exercises:  SAID Principle next blog….

There are many different steps you can take when beginning a strength and conditioning program.  The first step is to get your doctor’s approval!  With your doctor’s permission you can begin by assessing your fitness level.  The big question in terms of fitness is “where are you at?”  It’s best if you determine at least a few things about your current fitness level so you can set realistic goals and have a standard for measuring your improvement.

The three key components that encompass total physical fitness are strength, flexibility, and endurance. The following physical fitness tests and corresponding desired norms for physical fitness are based on the nationally accepted fitness test standards for ages 18 and older.  Tests can be performed in any order and you have the option to test yourself in all areas or only a few.  Testing is intended to give you a good representation of your current fitness level and how well you will perform specific training activities. 

The President’s Challenge Adult Fitness Test website is an excellent resource for the physically active.  The website has links that will take you to in depth instructions and tips on performing each test.  After completing the tests you can enter your data online to receive an evaluation. 

The President’s Challenge Adult Fitness Test Website Link

Data Entry Online Link

Physical Assessment Tests and Desired Norms

STRENGTH

1.  Pushups

Pushup Standards:

Male: Average = 30; Excellent = 50

Female: Average = 7; Excellent = 25

2.  Pullups

Pullup Standards:

Male: Average = 8; Excellent = 13

Female: Average = 1; Excellent = 8

Flexed Arm Hang: (Alternative, if no pullups can be completed)

Flexed Arm Hang Standards:

Male: Average = 30 seconds (no Excellent standard for males as they should be able to perform pullups)

Female: Average = 7 seconds; PFT perfect score 1 min.,10 seconds

3.  Curl-ups (Situps):

Situps Standards:

Male: Average = 44; Excellent = 55

Female: Average = 34; Excellent = 44

FLEXIBILITY

1.  Sit and Reach Test

Sit and Reach Standards:

Male: Average = 15.5"; Excellent = 18.6"

Female: Average = 16"; Excellent = 19"

2.  V-Sit and Reach

V-Sit Standards:

Male: Average = 3"; Excellent = 7"

Female: Average = 4.5"; Excellent = 8"

ENDURANCE

1.  One mile run/walk

One Mile Standards:

Male: Average = 7:35; Excellent = 6:30

Female: Average = 10:51; Excellent = 8:22

2.  3 Minute Step Test (alternative to 1 mile run)

3-min. Step Test Standards:

National Strength and Conditioning Association Position Statements

Health Aspects of Resistance Exercise and Training

http://www.nsca-lift.org/publications/health aspects of resistance training.pdf

Youth Resistance Training

 http://www.nsca-lift.org/youthpositionpaper/Youth_Pos_Paper_200902.pdf

Basic Guidelines for the Resistance Training of Athletes

http://www.nsca-lift.org/publications/Basic guidelines for the resistance training of athletes.pdf

Explosive/ Plyometric Exercises

http://www.nsca-lift.org/publications/PLYOforWeb.pdf

The Squat Exercise in Athletic Conditioning

http://www.nsca-lift.org/publications/SQTforWeb.pdf