Caffeine Timing Revisited: Taking Your Caffeine Supplement During (Longer) Workouts Works, Too - Ca. 4% Faster Times

Yes, it may in fact make sense to shovel down another scoop of your preworkout if you train for 2h. Just try to remain below the sign. stress-dosage of 600-800mg caffeine/day (Beaven. 2008).
I have previously addressed the question "When is the Best Time to Consume Your Pre-Workout Caffeine?", so why do I need to revisit it? Well, the answer is, as you'd expect, the publication of new scientific evidence which suggests that you can also consume your caffeine much later and still see performance gains.

The aim of said study was to assess if low and moderate doses of caffeine delivered in a carbohydrate-electrolyte solution (CES) late in exercise improved time trial (TT) performance. Fifteen (11 male, 4 female) cyclists (22.5 ± 0.9 yr; 69.3 ± 2.6 kg; VO2peak, 64.6 ± 1.9 ml / min / kg-1) completed four double-blinded randomized trials.
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Subjects completed 120 min of cycling at ~60% VO2peak with five interspersed 120 s intervals at ~82% VO2peak, immediately followed by 40 s intervals at 50 W. Following 80 min of cycling, subjects either ingested a 6% CES (PL), a CES with 100 mg (low dose, 1.5 ± 0.1 mg  / kg body mass) of caffeine (CAF1) or a CES with 200 mg (moderate dose, 2.9 ± 0.1 mg / kg body mass) of caffeine (CAF2).
Table 1: Overview of caffeine timing in previous studies (from Talanian. 2016); here the study by Cox et al. (2002) may be of greatest interest, because it shows that a very low dose (~1.3 mg / kg)ingested 20-40 min before the TT improved performance to a similar extent to a high moderate dose (6 mg  / kg) initially ingested 120 or 180 min before the TT.
Now, it is important to understand that after 80 minutes of cycling, the time trial was conducted 40 (total 120) minutes after the ingestion of the caffeine at a constant resistance requiring the subjects to invest 6 kJ /kg body weight to "finish" (e.g. you weigh 80 kg, you have to burn 2400 kJ).

Figure 1: Effects of placebo, 1,5 mg/kg (CAF1) and 2.9 mg/kg (CAF2) on time trial performance in minutes and power output in watts (Talanian. 2016); both dosages work, but CAF2 is clearly superior to CAF1; there was no difference between respiratory, heart rate, glucose, free fatty acid, body weight, hematocrit or USG measurements between treatments.
The results of the study are nevertheless intriguing: the CAF2 (26:36 ± 0:22 min:sec) TT was completed faster than CAF1 (27:36 ± 0:32 min:sec, p < 0.05). It does therefore appear to be certain that "both doses of caffeine delivered late in exercise improved TT performance over the PL trial and the moderate dose (CAF2) improved performance to a greater extent than the low dose (CAF1)" (Talanian. 2016).
Figure 2: We do have good evidence that high dose caffeine can be too much of a good thing... at least if you measure "good thing" via the testosterone to cortisol ratio which will decrease after 800 mg by 14%; ± 21% (Beaven. 2016).
Before I wrap this up, with a reminder on limitations of the study design, I would like to put the results of Beaven's 2008 study into the potentially counter-productive effects of high(er) dosage caffeine on the cortisol to testosterone ratio, of which the scientists from the Horticulture and Food Research Institute of New Zealand were able to show that it is dose-dependently modulated by caffeine intake - with 600mg maximizing and 800mg reducing the T:C ratio, again.
Fig 3: Cox' study was sort of an intra-workout study, too (Cox. 2002).
Remember: This is not an "intra-workout" supplementation study in the strict sense. The caffeine was administered after what you may call "round one" of the workout. A similar situation may occur when do you cardio first and then want to HIIT the weights later in the workout... well, sort of similar.

Eventually, it would be more interesting to see if a longer time-trial (like a marathon) would still benefit from consuming caffeine at similar dosages a few minutes in, e.g. 200 mg after 10 minutes - would this allow a runner to hit is normal personal best on the marathon track?

Well this exact study has not been done yet, but the previously cited study by Cox et al. did compare the effects of high dose to lower-dose pre- vs. intra-ingestion of caffeine and found only a non-significant advantage when their subjects consumed 6mg/kg caffeine 60 minutes before vs. smaller amounts every 20 minutes during a steady-state 2h pre-test (time trial | see Figure 3) activity. This is not the study I would like to see, but it appears to suggest that benefits could be observed in my marathon example, too | Comment!
  • Beaven, C. Martyn, et al. "Dose effect of caffeine on testosterone and cortisol responses to resistance exercise." International journal of sport nutrition and exercise metabolism 18.2 (2008): 131.
  • Cox, Gregory R., et al. "Effect of different protocols of caffeine intake on metabolism and endurance performance." Journal of Applied Physiology 93.3 (2002): 990-999.
  • Talanian, Jason L., and Lawrence L. Spriet. "Low and Moderate Doses of Caffeine Late in Exercise Improve Performance in Trained Cyclists." Applied Physiology, Nutrition, and Metabolism ja (2016).
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