Aerobic threshold

Lactate inflection point (LIP), is the exercise intensity at which the blood concentration of lactate and/or lactic acid begins to exponentially increase. Often expressed as 85% of maximum heart rate or 75% of maximum oxygen intake. When exercising at or below the LT, any lactate produced by the muscles is removed by the body without it building up.

The onset of blood lactate accumulation (OBLA) is often confused with the lactate threshold. With a higher exercise intensity the lactate production exceeds at a rate which it cannot be broken down, the blood lactate concentration will show an increase equal to 4.0mM; it then accumulates at the muscle and then moves to the bloodstream.

Regular endurance exercise leads to adaptations in skeletal muscle which prevent lactate levels from rising. This is mediated via activation of PGC-1α which alters the isoenzyme composition of the LDH complex and decreases the activity of the lactate generating enzyme LDHA, while increasing the activity of the lactate metabolizing enzyme LDHB.

The lactate threshold is a useful measure for deciding exercise intensity for training and racing in endurance sports (e.g., long distance running, cycling, rowing, long distance swimming and cross country skiing), but varies between individuals and can be increased with training.

Interval training uses different work and rest periods allowing the body to temporarily exceed the lactate threshold at a high intensity, and then recover (reduce blood-lactate). This type of training uses the ATP-PC and the lactic acid system whilst exercising, which provides the most energy when there are short bursts of high intensity exercise followed by a recovery period. Interval training can take the form of many different types of exercise and should closely replicate the movements found in the sport. Interval training can be adjusted to the individual, however it is important to consider the intensity of each interval, duration or distance of each interval, length of rest/recovery, number of repetitions, frequency of training and recovery type.

Fartlek and interval training are similar, the main difference being the structure of the exercise. Fartlek is a Swedish word, meaning speed play. This type of training is a combination of continuous (generally aerobic) and interval training (generally anaerobic), involving consistent changes of pace/intensity throughout the session.

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