by Robh » Tue Jan 20, 2009 1:59 pm
From Juerg :-
"Effects of detraining on the major physiological systems "
Cardio-respiratory detraining :-
Maximal oxygen uptake (VO2max) has been shown to decline by anything from 4-20% with inactivity of two weeks or more (2-5).
With detraining of endurance-trained athletes blood volume is reduced by 5-12% within the first two days (6). This reduction in blood volume is the primary reason for the observed rapid decline in cardiovascular function (4). As a direct result there is a decrease in cardiac output (amount of blood pumped per minute) and stroke volume (amount of blood pumped per beat) with an attendant increase in heart rate during submaximal exercise – consistent with the equation
Respiratory function is also altered with inactivity. Maximal voluntary ventilation has been shown to decrease by 10-14%, while in the longer term the ventilatory response to increasing carbon dioxide levels increases after two years without training. It also appears that the energy cost of breathing is increased with detraining as increasingly more blood flow is ‘stolen’ by respiratory muscles working at more than 55% of forced vital capacity (7,8).
Metabolic detraining:-
Respiratory exchange ratio (RER) is calculated from the amount of oxygen consumed versus the amount of carbon dioxide produced during exercise, and gives an indication of which fuels (fat, carbohydrate and protein) predominate. After detraining has occurred, there’s a comparative increase in the amount of carbohydrate used as fuel during both maximal and submaximal exercise, with less energy derived from fat (12,14).
As a consequence of hard training at or close to lactate threshold for a number of weeks, two main adaptations occur providing evidence of improved endurance: reduced submaximal blood lactate and a higher exercise intensity before lactate threshold is reached (see box below). However, with detraining the opposite occurs, and higher blood-lactate concentrations have been measured in swimmers and in endurance-trained runners and cyclists at a lower percentage of VO2max after just a few days of inactivity. However, when compared to sedentary individuals, those previously highly trained still have a lactate threshold at a higher percentage of their VO2max, even after detraining."