Background
It is well documented that high intensity interval training (HIIT) is a time
efficient and effective method of training to improve exercise performance.
However, there are a wide range of intervention protocols used in both
research and applied fields, making comparison of data difficult. Previous
work from our laboratory (Lloyd-Jones et al., under review) suggested that the
work:rest ratio used during this type of training may be important in
determining adaptations, and in selecting the most efficient training approach,
although this a poorly understood and often neglected consideration.
Therefore the aim of this study is to compare different work:rest ratio, all using
a 6 second sprint but with either a 1:8, 1:10 or 1:12 work:rest ratio.
Methods
35 active male and females (age: 24 ± 4 years, height: 1.77 ± 0.09m, body
mass: 74.7 ± 12.9kg, body fat: 16.8 ± 6.1%, height, body mass, body fat)
initially completed a VO2max step test, followed at least 24hrs later by a thigh
occlusion test whilst wearing near-infrared spectroscopy over the vastus
lateralis muscle, and a 10km cycling time trial.
Participants then completed 6 sessions of HIIT on a cycle ergometer split over
2 weeks, consisting of 10x6 sec sprints with either 48sec rest (1:8 group),
60sec rest (1:10 group) or 72sec rest (1:12 group), and compared with a
control group in a randomised controlled trial. Peak and average power output
were calculated for each sprint session and peak power calculated for each
individual sprint.
Results
There was no significant change in VO2max following 2 weeks of training in
any group, or 10km time trial performance (1:8: pre: 780 ± 258sec post: 751 ±
270sec, 1:10 pre: 572 ± 138sec post: 563 ± 134sec, 1:12: pre: 641 ± 100sec
post: 615 ± 94sec, Con: pre: 716 ± 207sec post: 761 ± 229sec). Peak power
output increased significantly in the 1:8 group (1038 ± 330 -1095 ± 357 watts),
1:10 group (1092 ± 282 - 1148 ± 286 watts) and 1:12 group (1043 ± 201 -
1097 ± 226 watts). The average range of the change in power over the
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training session, for all the six sprint sessions for the 1:8 group was 62watts,
the 1:10 group was 44watts and the 1:12 group was 45watts. There was no
change in muscle oxygen kinetic data in any group following 2 weeks of HIIT
as assessed by thigh occlusion.
Conclusion
The performance improvements in 10km time trial performance were largest
in the 1:8 and 1:12 groups. It is possible that there was insufficient recovery
time in the 1:8 condition, resulting in metabolic stress to the cardiovascular
system, and that adaptations in the 1:12 condition may be a consequence of
repeatedly achieving peak power output, facilitated by a sufficient recovery
period. It is therefore possible that adaptations following HIIT can be elicited
from different stimuli, and this should be considered in future research and
practice
