VO2 max decreased by seven percent after 12 days, 14 percent after 56 days and 16 percent by day 84. Cardiac output declined by around 10 percent by day 84, declining by around seven percent after 12 days. Stroke volume decreased by 11 percent in the first 12 days and stabilized at a loss of 14 percent by day 84.
Heart rate increased during the detraining period, which partially compensated for decreases in stroke volume.
Many athletes confused about training seek to achieve the highest heart rate possible during workouts. As athletes achieve fitness, heart rate decreases. This makes achieving higher heart rates during training more difficult.
In separate research, when scientists looked at combined study results, it appears that blood-lactate concentrations increase exponentially when training ceases and a steady state level is reached around the 21- to 28-day mark.
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Biopsy data
Key enzymes that are essential to aerobic respiration decline and reach their lowest levels by day 56. Interestingly, myoglobin (the primary oxygen-carrying pigment of muscle tissue) and capillary density (affecting the volume of blood flow into muscles) were not affected by the detraining.
Two Phases of Fitness Loss
It appears that there are two distinct phases of fitness loss in highly trained athletes when they cease training. The first phase lasts some 21 to 28 days and is attributed to central adaptation losses. You can think of it as losses to your cardiovascular system.
The second phase is considered peripheral or linked to losses specific to trained muscles and muscle fiber changes.
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Changes in Strength
A separate study examined strength training in two mixed groups of men and women. The first group included those 20 to 30 years old and the second was 65 to 75 years old. The groups followed a strength program for nine weeks and then allowed 31 weeks of detraining to occur.
Using one-repetition maximum and isokinetic strength as the measurements, the study found no significant differences in strength gains or losses between the women and men in each group. This means gender had no effect on the percentage of strength gains and losses.
What's striking is that after 31 weeks of detraining, the young group lost around eight percent of their strength; however, the older group lost around 14 percent. Strength training losses in older athletes is more than in the younger group.
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Detraining or the Reversibility Principle
As you probably expected, if you quit training you will lose fitness. Science refers to this phenomenon as detraining or the reversibility principle. Scientists collected results from several studies to find the following average results for two periods of detraining. Short-term (ST) was three weeks or less and longer-term (LT) was 3 to 12 weeks.
- VO2 max decreased eight percent ST and 18 percent LT.
- Lactate threshold decreased seven percent ST and 18 percent LT.
The good news is that if you reduce training and keep some intensity in the training mix, you can significantly reduce your losses. This allows for recovery from the racing season without resetting your fitness to zero. This will be covered in Part II.
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