After listening to the first half of the podcast, I read the DMS article on the Scott Janish site and then the article cited under the Yeast Storage/Health section: Yeast Handling Studies. I. Agitation of Stored Pitching Yeast.
The study involved yeast which was collected from a production fermenter and then stored (for 5 days at 1 degree Celsius) under beer with no agitation, under water with 2 hours of agitation per day, or under water with constant stirring via a Corning magnetic stirrer. It did not involve making starters.
The yeast stored under water with constant agitation decreased in viability by 25% and in glycogen by 85%. The yeast stored still under beer or under water with 2 hours of agitation per day decreased in viability by 8% and in glycogen content by 12%.
The authors suggested that the oxygen provided to the yeast by stirring accelerated the metabolic processes of the cells which required expenditure of stored cellular glycogen. They then noted that had this occurred in wort the glycogen could have been used by the cells to form sterols, possibly in “a concentration sufficient to negate the need for wort oxygenation and to shorten the initial lag phase after pitching” (assuming all the glycogen dissimilated during storage was so used). However, since the yeast was stored in water under nutrient-deficient conditions, this did not occur. Once the stored glycogen was depleted, the cells died.
Further, they stated that additional cell losses may have been caused by oxygen toxicity.
Interestingly, they also estimated that 15% of the of the original cells were lost through mechanical breakage caused by stirring, and this may have resulted in an increase of respiratory deficient mutants (from 1% to 15% of the population) which are believed to be better protected from mechanical breakage due to their smaller size.