Question for Science-minded swimmers...

First let's agree that not everything is being lost in a matter of a week or two. The loss in fitness that occurs in such a small period of time is mainly due to a drop in cardiac output (caused by a drop of plasma volume) as well as a drop of intramitochondrial enzyme efficiency. Think of those enzymes as being the employees that process a large portion of metabolic functions within the mitochondria. With fitness, these employees are capable of processing more metabolic at a higher rate. With a two week brake, they just need a week or two to regain this loss efficiency. Also, some hormones tend to overreact a bit after this sort of break. Drop in cardiac output along with increased activity of adrenalin for instance tend to increase the heart rate (sometimes considerably). Following 5 months of competitive training (approximately 9,000 yards.d-1, 6 d.wk-1), three groups of eight male swimmers performed 4 wk of either reduced training (3,000 yard.session-1) or inactivity. Two groups reduced their training to either 3 sessions.wk-1 (RT3) or 1 session.wk-1 (RT1), whereas the third group (IA) did no training. Measurement of muscular strength (biokinetic swim bench) showed no decrement in any group over the 4 wk. In contrast, swim power (tethered swim) was significantly decreased (P less than 0.05) in all groups, reaching a mean change of -13.6% by week 4. Blood lactate measured after a standard 200-yard (183 m) front crawl swim increased by 1.8, 3.5, and 5.5 mM over the 4 wk in groups RT3, RT1 and IA, respectively. In group RT1, stroke rate measured during the 200-yard swim significantly increased (P less than 0.05) from 0.54 +/- 0.03 to 0.59 +/- 0.03 strokes.-1 while stroke distance significantly decreased (P less than 0.05) from 2.50 +/- 0.08 to 2.29 +/- 0.13 m.stroke-1 during the 4-wk period. Both stroke rate and stroke distance were maintained in group RT3 over the 4 wk of reduced training. Group IA was not tested for stroke mechanics. Whereas maximal oxygen uptake decreases significantly (P less than 0.05) over the 4 wk in group RT1 (4.75 to 4.62 l.min-1), no change in maximal oxygen uptake was observed in group RT3. These results suggest that aerobic capacity is maintained over 4 wk of moderately reduced training (3 sessions.wk-1) in well-trained swimmers. Muscular strength was not diminished over 4 wk of reduced training or inactivity, but the ability to generate power during swimming was significantly reduced in all groups. It's several things. Some happen right away, some take longer. If you want to read the scientific literature on this, the term to search is "deconditioning." As in, the opposite of conditioning. Every adaptation that your body makes to training gets lost if you don't keep training. Off the top of my head: Skill memory Motor unit recruitment efficiency Enzymes in energy pathways Physical muscle changes (e.g., capillary density) If you're really interested in this stuff, read Maglischo. Fantastic explanation! I was looking for this type of answer. I should have not put in my original question any reference to being "sick". I should have used an example of a world class athlete (ie- Ryan Lochte) who is otherwise healthy that takes a 2 week vacation and his first day back in the pool he is not swimming the same workout splits that he was swimming prior to "Worlds" or the "Olympics" Thank you everyone for your answers!!

First let's agree that not everything is being lost in a matter of a week or two. The loss in fitness that occurs in such a small period of time is mainly due to a drop in cardiac output (caused by a drop of plasma volume) as well as a drop of intramitochondrial enzyme efficiency. Think of those enzymes as being the employees that process a large portion of metabolic functions within the mitochondria. With fitness, these employees are capable of processing more metabolic at a higher rate. With a two week brake, they just need a week or two to regain this loss efficiency. Also, some hormones tend to overreact a bit after this sort of break. Drop in cardiac output along with increased activity of adrenalin for instance tend to increase the heart rate (sometimes considerably). Following 5 months of competitive training (approximately 9,000 yards.d-1, 6 d.wk-1), three groups of eight male swimmers performed 4 wk of either reduced training (3,000 yard.session-1) or inactivity. Two groups reduced their training to either 3 sessions.wk-1 (RT3) or 1 session.wk-1 (RT1), whereas the third group (IA) did no training. Measurement of muscular strength (biokinetic swim bench) showed no decrement in any group over the 4 wk. In contrast, swim power (tethered swim) was significantly decreased (P less than 0.05) in all groups, reaching a mean change of -13.6% by week 4. Blood lactate measured after a standard 200-yard (183 m) front crawl swim increased by 1.8, 3.5, and 5.5 mM over the 4 wk in groups RT3, RT1 and IA, respectively. In group RT1, stroke rate measured during the 200-yard swim significantly increased (P less than 0.05) from 0.54 +/- 0.03 to 0.59 +/- 0.03 strokes.-1 while stroke distance significantly decreased (P less than 0.05) from 2.50 +/- 0.08 to 2.29 +/- 0.13 m.stroke-1 during the 4-wk period. Both stroke rate and stroke distance were maintained in group RT3 over the 4 wk of reduced training. Group IA was not tested for stroke mechanics. Whereas maximal oxygen uptake decreases significantly (P less than 0.05) over the 4 wk in group RT1 (4.75 to 4.62 l.min-1), no change in maximal oxygen uptake was observed in group RT3. These results suggest that aerobic capacity is maintained over 4 wk of moderately reduced training (3 sessions.wk-1) in well-trained swimmers. Muscular strength was not diminished over 4 wk of reduced training or inactivity, but the ability to generate power during swimming was significantly reduced in all groups. It's several things. Some happen right away, some take longer. If you want to read the scientific literature on this, the term to search is "deconditioning." As in, the opposite of conditioning. Every adaptation that your body makes to training gets lost if you don't keep training. Off the top of my head: Skill memory Motor unit recruitment efficiency Enzymes in energy pathways Physical muscle changes (e.g., capillary density) If you're really interested in this stuff, read Maglischo. Fantastic explanation! I was looking for this type of answer. I should have not put in my original question any reference to being "sick". I should have used an example of a world class athlete (ie- Ryan Lochte) who is otherwise healthy that takes a 2 week vacation and his first day back in the pool he is not swimming the same workout splits that he was swimming prior to "Worlds" or the "Olympics" Thank you everyone for your answers!!