Hill, Karen M (2017) How do different dietary dairy proteins, ingested post-exercise, effect adaptations to endurance training? PhD thesis, Victoria University.

Abstract

It is well established that endurance exercise training leads to cardiovascular, skeletal muscle, and metabolic adaptations, with important implications for both athletic performance and health. While many studies have addressed the effects of endurance exercise training on such adaptations, very few have examined the role of post-exercise nutritional supplementation in facilitating or increasing the magnitude of the adaptive response. The beneficial effects of post exercise nutrition, in the form of carbohydrate and protein, following an acute bout of exercise has been the focus of many investigations. The results however remain equivocal due to methodological differences, such as the training status of participants, the treatment groups not being isocaloric, differing CHO contents, different protein sources, exercise modes and protocols, and outcome measurements all being different. The quality of the protein source used in post exercise supplementation may also affect training adaptations. Animal-source of proteins, such as milk and the constituent proteins of milk, casein and whey, are classified as being of high biological availability and quality. The types of proteins that are best for achieving muscle recovery and adaptations after endurance exercise are not defined. The significant aim of this PhD candidature was to determine the role of protein supplementation, when included in the training diet over an extended period, on endurance training adaptations. Along with investigating how different proteins affect the signalling pathways that regulate endurance training adaptations. As such the research presented in this thesis examines 8 weeks of supplementation, with and without an endurance training program, with micellar caseins or caseinates, whey protein isolates or a carbohydrate matched and isocaloric group in animal and human models. The first study demonstrated that after 8 weeks of supplementing with whey protein isolates, this group had lower body fat compared to the carbohydrate group at week 4 (P < 0.05) and week 8 (P < 0.05). The micellar caseins group had lower body fat compared to carbohydrate group only after 8 weeks (P < 0.05). A key finding in the second study was that despite matching all rodents across groups according to exercise performance, the carbohydrate supplemented animals were unable to perform for as long in the time to exhaustion test compared to both whey protein isolates and micellar caseins groups (P < 0.05); 14:19 ± 4 min, 29:81 ± 11 min and 25:51 ± 6 min.. There was no significant difference between protein groups in several measures including; enzyme activity of citrate synthase and β-hydroxyacyl-CoA dehydrogenase (βHAD), mitochondrial respiration or lean mass. The third study examined post-exercise supplementation with calcium caseinates compared to whey protein isolates in trained cyclists in a double-blind manner. Participants were provided all meals and snacks for the duration of the study. Endurance exercise performance, body composition and mitochondrial respiration, along with proteins involved in mitochondrial biogenesis showed no difference between protein groups after 8 weeks of supplementation and endurance training. This research has established that micellar caseins and whey protein isolates may have beneficial effects on body composition and mitochondrial function without exercise, however following exercise training these mitochondrial function differences are diminished. Despite this, animals supplemented with the different proteins and undertook an endurance training protocol for 8 weeks performed significantly better in the time to exhaustion test. Thus, it appears that this improved time to exhaustion is not related to improved mitochondrial function, but by some other, yet to be determined factor.

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