So, the last newsletter wasn’t well received. I have been politely informed that it was too bogged down with minutia. Point taken. Nobody wants to see the sausage making, they just want the final product. Hopefully this edition will redeem the integrity of the newsletters. I put a lot of work into this one and even made literature references!
If you’re pressed for time (aka “no sausage making for me, thanks”) here’s the quick and dirty version of the whole newsletter: If you’re injured, can’t run or do cross-training, you’re in big trouble. You lose significant amounts of fitness in a matter of 2-3 weeks. On the other hand, if you do cross training while you’re injured, you’ll be fine (not ideal, but fine). That’s the newsletter. If you want the details, here is the minutia…
The injured athlete is the perfect expression of frustration. Whether it’s the classic overuse injury like shin splints, iliotibial band syndrome and plantar fasciitis, or it’s an acute injury like rolling your ankle a month before an Ironman. You just can’t run and it’s as frustrating as people who start sentences with “To be honest with you…”
In either case, there is the overwhelming dilemma: “If I take time off, how much of my previous hard work will be lost?” Let’s take a (quick) look at how time off affects different systems in the body and how to mitigate the losses.
VO2max: The negative effect on VO2max due to detraining varies a bit with different studies, with losses ranging from 4-14% when training is stopped for less than 4 weeks [1-8]. Obviously, the longer the inactivity, the more the negative impact on VO2max., to a point. For example one study found that endurance athletes lost 7% of their VO2max in the first 21 days of inactivity and eventually stabilized at a 16% loss after 56 days . For what it’s worth, you can calculate (here) an estimate that if you normally run a 23:00 minute 5K, a 7% loss in VO2max would result in about 90 seconds (24:30) slower for the 5K.
A different study found that over a 2400 meter run, women averaged 21 seconds slower following 15 days of inactivity. 
The better trained you were before the inactivity (higher trained-state VO2max), the bigger its decline when training is stopped .
Blood Volume: The majority of the detraining effects can be traced back to decreased blood volume. Total blood volume and plasma volume has been shown to decline by 5-12% [5,7,9,10] within a few weeks.
Stroke Volume: This is the amount of blood pumped out by one heartbeat. This has been shown to decline by 10 to 17% after 12 to 21 days of training cessation [1,2,5]. This is likely due to the decreased blood volume
Heart Rate: Since the heart is now pumping less blood per stroke, (because of the reduced blood volume) the heart has to pump more times. Results confirm this, as sub maximal and maximal heart rate will increase by about 5-10% [1,5,7,9].
Endurance Performance: Swimmers were found to be 7 seconds slower in a 400 meter freestyle swim after 10 days of inactivity . Other studies show a 4-25% reduction in time to exhaustion for endurance trained athletes [4,5-8,12]. The good news is that in runners at least, there was no change in running economy . This means that most of the detraining effects were cardiovascular in nature. This is important because as we will see later, if you can keep your cardiovascular fitness with some sort of cross-training, it will mitigate the negative effects of not running.
So as I mentioned above, I will not get into the details like changes seen in myoglobin, enzymatic activity, lactate kinetics etc. However, I do want to mention that studies show no change in muscle fiber distribution , muscle cross section area [7,17]or strength with a few weeks of inactivity in endurance athletes (this does not pertain to strength athletes). Again, this is important to know because it tells us that most of the detraining effects are seen in the cardiovascular system, not the muscular system. So if you keep your cardio training up with a different aerobic exercise you won’t lose as much VO2max, blood volume etc. Not an ideal scenario, but it helps as we see here:
32 trained subjects underwent a 2 mile running time trial and had their VO2max tested. They were then randomly assigned to water running, cycling, or running training for 6 weeks. After 6 weeks of training, all groups made a small but statistically significant decrease in VO2max. Most importantly, regardless of training modality, there was no change in 2-mile run time. It was concluded that over a 6-week period, runners who cannot run because of soft tissue injury can maintain VO2max and 2-mile run performance similar to running training with either cycling or water running .
Running endurance time and VO2max was tested in 42 untrained subjects. They then went through a 9 week training program of either in-line skating, running or no training. The treadmill time and the VO2max was equally improved in the runners and the skaters, but no change in the control group who did nothing .
A 5 week training session of either running only, or 50/50 running/cycling resulted in the same amount of improvements in VO2max and 5K time trial 
22 Women were assigned to a treadmill, elliptical or stairmaster 3X/week for 12 weeks. At the end of the study, all three groups had similar improvements in VO2max .
That’s all for now folks.
1. Coyle EF, Martin III WH, Sinacore DR, et al. Time course of loss of adaptations after stopping prolonged intense endurance training. J Appl Physiol 1984; 57 (6): 1857-64
2. Martin III WH, Coyle EF, Bloomfield SA, et al. Effects of physical deconditioning after intense endurance training on left ventricular dimensions and stroke volume. J Am Coll Cardiol 1986; 7 (5): 982-9
3. 48. Moore RL, Thacker EM, KelleyGA, et al. Effect of training/detraining on submaximal exercise responses in humans. J Appl Physiol 1987; 63 (5): 1719-24
4. Houston ME, Bentzen H, Larsen H. Interrelationships between skeletal muscle adaptations and performance as studied by detraining and retraining.Acta Physiol Scand 1979; 105: 163-70
5. Coyle EF, Hemmert MK, Coggan AR. Effects of detraining on cardiovascular responses to exercise: role of blood volume. J Appl Physiol 1986; 60 (1): 95-9
6. Ghosh AK, Paliwal R, SamMJ, et al. Effect of 4 weeks detraining on aerobic and anaerobic capacity of basketball players and their restoration. Indian J Med Res 1987; 86: 522-7
7. Houmard JA, Hortobágyi T, Johns RA, et al. Effect of shortterm training cessation on performance measures in distance runners. Int J Sports Med 1992; 13 (8): 572-6
8. Houmard JA, Hortobágyi T, Neufer PD, et al. Training cessation does not alter GLUT-4 protein levels in human skeletal muscle. J Appl Physiol 1993; 74 (2): 776-81
9. Cullinane EM, Sady SP, Vadeboncoeur L, et al.Cardiac size and VO2max do not decrease after short-term exercise cessation. Med Sci Sports Exerc 1986; 18 (4): 420-4
10. Thompson PD, Cullinane EM, Eshleman R, et al. The effects of caloric restriction or exercise cessation on the serum lipid and lipoprotein concentrations of endurance athletes. Metabolism 1984; 33 (10): 943-50
11. Claude AB, Sharp RL. The effectiveness of cycle ergometer training in maintaining aerobic fitness during detraining from competitive swimming. J Swimming Res 1991; 7 (3): 17-20
12. Madsen K, Pedersen PK, DjurhuusMS, et al. Effects of detraining on endurance capacity and metabolic changes during prolonged exhaustive exercise. J Appl Physiol 1993; 75 (4): 1444-51
13. Eyestone et al., Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. Am J Sports Med. 1993 Jan-Feb;21(1):41-4.
14. Melanson EL, Freedson PS, Jungbluth S. Changes in VO2max and maximal treadmill time after 9 weeks of running or in-line skating. Med Sci Sports Exerc 1996; 28(11):1422-6.
15. Mutton DL, et al., Effect of run vs combined cycle/run training on VO2max and running performance. Med Sci Sports Exerc. 1993 Dec;25(12):1393-7.
16. Egana M, Donne B. Physiological changes following a 12 week gym based stair-climbing, elliptical trainer and treadmill running program in females. J Sports Med Phys Fitness 2004; 44(2):141-6.
17. Wilber RL, Moffatt RJ. Physiological and biochemical consequences of detraining in aerobically trained individuals. J Strength Cond Res 1994; 8 (2): 110-24
18. Doherty et al., Fifteen-day cessation of training on selected physiological and performance variables in women runners. J Strength Cond Res. 2003 Aug;17(3):599-607