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Fiona Iredale, Frank Bell and Myra Nimmo

Fourteen sedentary 50- to 55-year-old men were exercised to exhaustion using an incremental treadmill protocol. Mean (±SEM) peak oxygen uptake (V̇O2peak) was 40.5 ± 1.19 ml · kg1 · min−1, and maximum heart rate was 161 ± 4 beats · min−1. Blood lactate concentration was measured regularly to identify the lactate threshold (oxygen consumption at which blood lactate concentration begins to systematically increase). Threshold occurred at 84 ± 2% of V̇O2peak. The absolute lactate value at threshold was 2.9 ± 0.2 mmol · L−1. On a separate occasion, 6 subjects exercised continuously just below their individual lactate thresholds for 25 min without significantly raising their blood lactate levels from the 10th minute to the 25th. The absolute blood lactate level over the last 20 min of the steady-state test averaged 3.7 ± 1.2 mmol · L−1. This value is higher than that elicited at the threshold in the incremental test because of the differing nature of the protocols. It was concluded that although the lactate threshold occurs at a high percentage of V̇O2peak, subjects are still able to sustain exercise at that intensity for 25 min.