Friday, September 28, 2007

Fall Indoor Multirider Classes - Now Open!

Check out the latest action from our fall indoor class. These athletes are performing a field test to determine there training zones for the class. This also allows us to track their progress over the next 12 weeks. We have seen historically an average of 10% improvement after just 12 weeks!!! Enjoy

Wednesday, September 12, 2007

Notes - VO2max

VO2max is the maximal rate at which you can inspire oxygen (O2) from the environment and transfer to the muscles within the body during exercise. It can be measured using specific equipment which measures the O2 you breathe during a graded exercise test.

VO2max is largely influenced by genetics and heredity.

For an individual, the variables that determine VO2max are cardiac output (CO) (the amount of blood you pump with each heart beat) and the aVDO2 difference (the concentration of 02 in the arteriole blood minus the concentration of O2 in the venous blood, basically the amount of 02 you extract out of the blood as it rushes past the working muscle cells).

VO2max = CO * aVDO2

Cardiac Output is dependant upon:

Stroke Volume (SV) – the amount of blood pumped out of the hearts ventricle each beat.

Heart Rate (HR) – the amount of beats per minute

CO = HR * SV

With proper training, these mechanisms and the variables that influence them increase 1.) The amount of blood you get to the muscle with max exercise 2.) The amount of oxygen you can extract from the blood as it travels past the exercising muscle.

An increase in VO2max from endurance training is primarily the result of an increase in CO. In turn, the most influential variable to increase CO is the increase in stroke volume after training (aVDO2 plays a small role in increasing VO2max, it has more influence over work capacity at sub-maximal workloads).

Reasons for an increase in SV (and hence, CO)

1. An increase in the heart’s left ventricular dimension – the chamber becomes larger thereby storing more blood for each beat.

2. Increased contractility of the heart. The heart beats a little harder thereby decreasing the amount of blood volume left in the ventricle after it contracts.

3. An increase in the plasma volume (PV) of the blood (hypervolemia). With training you can increase the amount of blood in your body by as much as 20%. The Frank Starling Mechanism says that as the PV increases the end diastolic volume (EDV) (the amount of blood sitting in the left ventricle right before beating) thereby causing an increase in SV which increases CO.

↑ PV → ↑ EDV → ↑ SV → ↑ CO

Therefore, an increase in CO through specific endurance training means that at any given absolute sub-maximal workload there is less stimulation of the sympathetic nervous system (because blood pressure is maintained easier). This is the reason HR decreases (at rest and for a given absolute sub-maximal workload) after a block of training. There is also less blood flow redistribution during a given absolute sub-maximal workload due to an increased CO. This increases exercising blood lactate clearance, absorption of ingested food, and an increase in the formation of glucose by the liver. All of which make you a stronger endurance athlete.

Main point – Increasing your VO2max can benefit your performance at sub-maximal workloads, including lactate threshold, and this is primarily the result of an increase in the volume of blood you pump through your body during exercise.

Wednesday, September 5, 2007

*Notes - Lactate Threshold

During glycolysis (the breakdown of carbohydrate) pyruvate is formed. If the exercise intensity is low then pyruvate goes to the krebs cycle and produces energy using oxygen. If the exercise intensity is high then pyruvate is converted to lactate, along with other byproducts.

This process actually consumes some muscle energy. This inefficient form of energy production occurs because the muscle needs energy at a rate faster than can be supplied by oxidative phosphorylation (burning fat, aerobic) or via the krebs cycle (aerobic glycolysis).

Producing lactate also creates a byproduct called hydrogen ion (H+) which reduces muscle and blood pH (becomes more acidic). This is bad news for the muscle as H+ inhibits muscle contraction. (H+ displaces calcium within a muscle fiber, inhibiting cross-bridge cycling and reducing contraction force).

Contrary to what many may think it is not lactate that causes muscles to stop working or get sore after exercise (people afflicted with McArdle's disease cannot produce lactate and yet they still fatigue with exercise)

Lactate is formed even at rest, although at much lower levels, and is actually a preferred source of energy for the heart and slow-twitch muscle fibers (it gets converted back into ATP, the substance muscles need to contract and stimulates the liver to produce more glucose).

Lactate levels in the blood at rest are typically around 1-2 mmol and can exceed 20mmol during maximal exercise.

Lactate production and removal is a continual process within the muscle. As exercise intensity increases the rate of lactate production increases (our bodies need energy quickly at higher intensities and this pathway produces energy quickly, even at the expense of being inefficient). As intensity continues to rise higher lactate levels exceed the body's clearance capacity (via buffering or being used as a fuel source) and blood lactate levels rise precipitously.

The point where lactate begins to rise quickly is termed LT (Lactate Threshold) or OBLA (Onset of Blood Lactate Accumulation). These terms have replaced the misnomer "anaerobic threshold" because the muscle is never really out of oxygen as this term may imply.

Individual lactate threshold's typically occur around 4 mmol but can range from 3-6mmol depending on the individual.

(OK class pay attention – Extra credit)

*The limitation to exercise above the LT is not the increased levels of blood or muscle lactate but the associated increase in acidosis (H+) and other markers of muscular fatigue*

The physiological changes that occur at this threshold are significant for training the heart and lungs (metabolic acidosis, impaired muscle contraction, hyperventilation, altered oxygen kinetics, etc.).

Endurance training based around this threshold intensity has been shown to improve the absolute workload that can be performed at this threshold (increasing threshold power from 210 watts to 240 watts) as well as the percentage of VO2 max (increasing the threshold from 80% of VO2max to 85%).

This threshold and the percentage of VO2max it occurs are the single biggest predictors of you endurance performance.

To obtain your lactate threshold blood lactate samples are taken (via a finger tip prick) during an incremental exercise test and the results graphed to determine what intensity (HR, watts) a shift in production occurs. A separate VO2max test will further determine what potential an individual has for improvement of this threshold.