Which of the following is a common sign that an athlete is reaching their lactate threshold?

When an athlete is approaching their lactate threshold, the body starts to produce lactate at a faster rate than it can be cleared from the bloodstream, leading to a shift in energy production from aerobic to anaerobic metabolism. As a result, athletes may experience difficulty maintaining their pace during sustained efforts. This inability to sustain a desired pace is a key indicator that they have reached their lactate threshold, as the accumulation of lactate can lead to feelings of fatigue and discomfort.

The other options do not accurately reflect signs associated with reaching the lactate threshold. Consistently low heart rates would suggest the opposite of exertion and endurance, likely indicating a lower exercise intensity. Feeling refreshed and strong throughout exercise is indicative of being well below lactate threshold, as athletes typically do not encounter significant fatigue or discomfort in that state. Increased flexibility and range of motion are not related to metabolic changes or fatigue due to lactate accumulation; rather, they resemble physical conditioning and are not direct indicators of lactate threshold. Therefore, the inability to sustain pace is the most relevant sign of nearing this important physiological point during exercise.