Lactic acid is formed in small amounts, continuously, at rest and in moderate exercise. During light exercise, muscular energy demands are adequately met by reactions that consume oxygen. Any lactic acid formed in steady state exercise is rapidly oxidised by the heart and adjacent muscle fibres with high oxidative capacities. As such, the blood lactate level remains fairly stable.

Blood lactate does not accumulate at all levels of exercise. It is only when removal does not match production that blood lactate accumulates.

Onset of Blood Lactate Accumulation (OBLA)
During steady-rate exercise, aerobic metabolism is used to meet the energy requirements of the active muscles. Under these conditions, there is little or no accumulation of blood lactate.

• Lactate threshold refers to the highest exercise level/intensity (or level of oxygen uptake) that is not associated with an elevation in blood lactate concentration above the pre-exercise level (or an increase less than 1.0 mM). At this point anaerobic mechanisms are starting to be used to provide energy for the muscular work.
• Onset of blood lactate accumulation (OBLA) occurs when a level of 4.0 mM of lactate per litre of blood is attained. At this point substantially greater numbers of fast twitch fibres are being recruited and a much larger percentage of anaerobic glycolysis is being used to provide energy for muscular work.

Often, the terms lactate threshold and OBLA are used interchangeably, although their precise points of demarcation in terms of exercise intensity are different.

Specificity of the Point of OBLA
OBLA is specific to the exercise task. Differences in the point of OBLA occur in individuals when comparing bicycle, treadmill, and arm-crank exercise at all levels of oxygen uptake. This happens because of variations in the amount of muscle mass activated in the exercise. The metabolic rate per unit of active muscle mass is higher in arm-crank and bicycle exercise than in treadmill walking or running. Therefore, the point of OBLA would be reached at a lower exercise level during cycling and arm-crank exercise.

This indicates that different forms of exercise should not be used interchangeably to determine and quantify the point of OBLA.