The present data show that low dose bovine CPC supplementation provides a worthwhile improvement in TT40 performance following a period of HIT. In addition, there was a possible benefit of bovine CPC to enhance TT40 intensity and prevent a decrease in submaximal heart rate during HIT. Bovine CPC supplementation also provided a possible benefit to minimise fatigue and/or enhance recovery by maintaining ventilatory threshold 3–4 days following the HIT period.
Bovine CPC supplementation, when compared to the placebo, provided a likely benefit for TT40
performance at the end of a 5 day period of HIT. Improvements in time trial performance in already highly trained athletes following HIT are smaller than improvements in performance observed with untrained to moderately trained individuals following training.19,20
For highly trained athletes, a worthwhile improvement in performance is considered to be half of the coefficient of variation for that measure.16
The 1.65% improvement in TT40
for the bovine CPC group following HIT can be considered a small but worthwhile improvement as in our laboratory the coefficient of variation for TT40
performance following familiarisation is 0.9±0.7%.14
The placebo group experienced a slight decrease in TT40
3 performance from baseline, despite an increase in exercise intensity. Ronsen and colleagues21
have reported an increase in VO2
at the same submaximal exercise intensity when cyclists are fatigued from a prior bout of exercise, which may be the result of an increase in fat oxidation as a result of depleted muscle glycogen concentrations.21
The placebo group also experienced a decrease in average TT40
HR at the end of the HIT period, which may indicate greater fatigue when compared to the bovine CPC group. Declines in submaximal HR have also been reported by Verde et al22
and Lehmann et al10
following a period of intensified training, which has been associated with a decrease in performance.
Although the present data limit speculation as to the mechanism/s responsible for the improvements in TT40
performance for the bovine CPC group at the end of a 5 day HIT period, energy availability may have been enhanced. Increased muscle glycogen levels during normal training do not improve 1 h cycling performance23
or 45 min cycling performance (at an average intensity of 82% VO2max
However, during repeated days of high intensity exercise, enhanced muscle glycogen content may prevent and/or delay fatigue.25,26
Research has previously found that colostrum feeding in newborn calves increases plasma glucose concentrations and is associated with enhanced gluconeogenesis rate limiting enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase.27
Colostrum also contains IGF‐1 which has been found to enhance glucose uptake by skeletal muscle, independent of changes in GLUT‐4 protein.28
Whether bovine CPC improves muscle glycogen resynthesis during periods of intense training warrants investigation.
Research has previously found improvements in sprint and endurance running performance following bovine CPC supplementation at 8 weeks but not at 4 weeks.6,8
Somewhat consistent with this, the present study found the influence of bovine CPC on TT40
performance was unclear following 5 weeks of supplementation during normal training. However, in contrast, the effect on TT40
performance during normal training following 8 weeks of supplementation was also unclear. The disparate findings of enhanced performance in our previous work7
and an unclear influence on TT40
performance during normal training in the present study may be related to differences in the TT protocol used (2 h and 2.8 kJ/kg v
40 km in the present study) and fasting state. It is also possible that the smaller dose (10 g) of bovine CPC used in the present study may not have been sufficient to elicit the same improvements in performance during normal training periods as those reported by our group previously.7
It remains to be seen if a 10 g dose improves short duration (approximately 13 min) time trial performance following 2 h of submaximal endurance performance.
The five consecutive days of HIT were sufficient to induce short term fatigue in the placebo group, as evidenced by a decrease in ventilatory threshold. This is consistent with the findings of others,11,29
and it remains to be determined how bovine CPC, as shown in the present study, prevented the same degree of fatigue following HIT period. Cyclists in both groups seemed to have recovered from any residual fatigue resulting from the HIT period in 6–7 days; TT40
4 performance for both groups during the final week was faster than the TT40
3 completed at the end of the HIT period.
In contrast to the TT40
data, the influence of bovine CPC on TTF at 110% of the cyclists' ventilatory threshold was unclear. Both groups improved their TTF over the experimental period, however, there were no differences between the bovine CPC and placebo group. Previous literature has suggested that time to fatigue is a more sensitive marker of fatigue or over reaching than changes in VO2max
We hypothesised that we would observe a decrease in TTF in the placebo group, compared to the bovine CPC, in the week following the HIT period. While the placebo group experienced a decrease in ventilatory threshold 3–4 days following the HIT period, TTF performance, 5–6 days following the HIT period, remained unchanged. Cyclists in the placebo group may have recovered from any residual fatigue from the HIT period within 5–6 days.12
It is also possible that the mechanism responsible for improved TT40
performance is not associated with improvements in shorter duration exercise above threshold.
In summary, low dose bovine CPC supplementation was associated with a worthwhile improvement in TT40 performance and a reduction in fatigue following a 5 day HIT period. In addition, compared to placebo data, bovine CPC supplementation prevented a decrease in ventilatory threshold 3–4 days following the HIT period. The mechanism(s) for the observed performance improvements and reduction in fatigue following bovine CPC supplementation remain to be determined.
What is already known on this topic
- Colostrum is the first milk produced by mammals after parturition and contains high concentrations of growth and immune factors
- Bovine colostrum supplementation at 60 g/day enhances repeat running and cycling performance during normal training periods
What this study adds
- Bovine colostrum supplementation at 10 g/day enhances cycling performance during high intensity training
- Bovine colostrum supplementation at 10 g/day prevents a decrease in ventilatory threshold following a period of high intensity training