The influence of continuous vs split training protocols on endurance performance

Reports of twice daily training being used routinely by elite level endurance runners can be traced back to the 1960s. Coaches and runners have engaged in training protocols conducted during the foundational stage of training, that split the long, low intensity training (LIT) session into two sessions performed twice daily, in order to maintain volume of exercise (aligned with a single, long LIT session). Despite this, few studies to date have explored the acute physiological responses or the long-term (chronic) physiological adaptations to ‘twice daily training’. There is an assumption of parallel benefits of once daily training versus twice daily training based on total volume of exercise accumulated, however, this assumption has not been tested. The primary aim of this thesis was therefore to investigate the effects of once daily and twice daily training on factors associated with running performance.

Before addressing this primary aim, a comparison of a 5 km performance TT in both the laboratory and outdoor environments was made. The laboratory is commonly used a testing ground in scientific research, however, there are often questions over the ecological validity of laboratory-based trials and their transferability into a field based competitive environment. Results generated here demonstrate that there are significant performance differences in these environments. However, participants disclosed their discomfort when testing outdoors which drove the decision to limit all testing in Studies 2 and 3 exploring differences in once and twice daily training to the laboratory. Study 1 also derived four prediction equations designed to be used by athletes and coaches. Equations 1 and 2 were to predict laboratory 5 km TT times and 4 and 5 were to predict outdoor 5 km TT times.

Findings from Study 2 demonstrated that in the acute setting, significant differences are seen between once daily training and twice daily training for running economy (RE) (6.4 ± 2.9 mL.kg-1.km-1) (p = 0.033), respiratory exchange ratio (RER) (-0.05 ± 0) (p<0.001) and estimated fat metabolised (12.9 ± 2.4 grams) (p<0.001). Furthermore, the twice daily group did not reduce
their velocity over the course of the day to the same degree as the once daily group. These differences provided a rationale for investigating twice daily training as part of a training plan.

Findings from Study 3 demonstrated that when MTRs incorporate once or twice daily training as part of a six week training plan, significant differences were seen between the two groups in RER (-0.06) (p<0.001) and the estimated fat metabolised (13.3 grams) (p<0.001) during the long run.

Study 3 found significant differences in RER and substrate utilization of MTRs who performed either once or twice daily training as part of a six week training plan. The twice daily group used more CHO in the second run when compared with the second half of the once daily group’s run. As CHO is the more efficient fuel source for high intensity exercise such as a 5Km runs this will have contributed to the faster speeds observed for this group. Furthermore, while both groups saw significant improvements in a 5 km after performing either once daily (-13 ± 27 seconds) or twice daily (-30 ± 20 seconds) training plans, the group conducting the twice daily training saw significantly greater improvements (p = 0.03).

The findings in this research therefore demonstrate that, rather than previous suggestions that performance typically declines (Svedenhag & Sjodin, 1985) during the foundational stage of training where an increase in volume is achieved, conducting either of the once or twice daily training plans developed in Study 3 for six weeks resulted in improvements in 5 km RP.