This meta-analysis investigated "the role of exercise intensity and the trainability of VO2max". While I don't think that pursuing a higher VO2 Max should be a goal in training (I think it's more of a result of good training while pursuring performance goals), it is interesting to learn about the effectiveness of different intervals which can be applied in training.
A few interesting notes from the study are:
A total of 334 subjects (120 women) from 37 studies were identified. Participants were grouped into 40 distinct training groups, so the unit of analysis was 40 rather than 37. An increase in VO2max of 0.51 L ·min−1 was observed.
A subset of 9 studies, with 72 subjects, that featured longer intervals showed even larger (∼0.8–0.9 L · min−1) changes in VO2max with evidence of a marked response in all subjects.
The conventional wisdom is that intervals of 3–5 minutes are especially effective in evoking increases in exercise capacity. Consistent with this idea, the nine studies that generated the biggest increases in VO2max (∼0.85/min) generally used intervals of 3–5 minutes and high intensity continuous training.
PRACTICAL TAKEAWAY - intervals fo 3-5 duration are probably the most effective means of increasing VO2 Max. When I shared this there were some excellent replies and other useful data from shared on twitter so I'd encourage you follow those on Twitter.
INTERVALS: Active vs. passive recovery during an aerobic interval training session in well‑trained runners
How we perform intervals can be change the stimulus and how effective they are. The authors of this study set out to "compare cardio-metabolic, perceptual and neuromuscular responses to an aerobic interval training (AIT) run- ning session, with active (AR) vs. passive recovery (PR)".
The results were that:
There were no differences in time spent in the “red zone” (i.e. > 90% V̇O 2max ) between sessions, although the PR exhibited a greater time spent at peak V̇O2 close to significance.
However, the AR elicited a higher mean VO 2. The AR favored a lower [La] after sessions and a higher RPE during sessions.
Considering that PR elicited lower perceptual loading for a similar cardiorespiratory response, its use would be preferable, at least, for this type of AIT running sessions.
PRACTICAL TAKEAWAY - how you recover between intervals can slightly change the impact of the session, however, you shouldn't worry that passive resting will make the session too easy or reduce the benefit of intervals. I prefer a strategy of walking half the recovery interval and then jogging the second half to start the next interval from a moving state.
Studies that investigate the impact of eccentric exercise are important for trail runners as there is a large eccentric demand for downhill running. This study compared the rate of glycogen resynthesis between eccentric and concentric exercise.
The findings were that:
The glycogen content (mmol/kg dry wt) in the vastus lateralis of concentric leg (CL) muscles averaged 90, 395, and 592 mmol/kg dry wt at 0, 24, and 72 h of recovery.
The eccentric leg (EL) muscle, on the other hand, averaged 168, 329, and 435 mmol/kg dry wt at these same intervals.
In both groups, however, significantly less glycogen was stored in the EL than in the CL.
PRACTICAL TAKEAWAY - eccentric exercise can have significant impact on the rate of glycogen resynthesis. Consider that sessions with large amounts of downhill running may require greater recovery. As noted in the replies to this tweet, athletes who are accustomed to this type of exercise should see less of an impact on the rate of glycogen resynthesis.
Many athletes perform multiple training sessions a day which place significant demands on achieving an optimal nutrition strategy. This study "investigated the effect of consuming carbohydrate (CHO) and protein with water (W) following exercise on subsequent athletic (endurance/anaerobic exercise) performance".
The findings were that:
Ingesting CHO + W improved exercise performance compared with W.
Improvement was attenuated when participants were 'Fed' (a meal 2-4 h prior to the initial bout) as opposed to 'Fasted'.
Ingesting PRO + CHO + W did not affect exercise performance compared with CHO + W.
PRACTICAL TAKEAWAY - if you're doing multiple training sessions in a day, make sure to eat enough CHO throughout the day and around the sessions.