The role of exercise intensity and contraction frequency in modulation of exercise response
Murphy, EndaORCID: 0000-0002-5999-9096
(2023)
The role of exercise intensity and contraction frequency in modulation of exercise response.
PhD thesis, Dublin City University.
High intensity exercise been shown to produce different acute exercise responses when
compared to moderate intensity. Manipulating the rate of muscle contraction to alter intensity
has received limited research. The primary purpose of this PhD was to investigate the potential
mechanism that produces the acute differences observed when comparing high and moderate
intensity exercise. Altering exercise intensity will be achieved through increased force and rate
of contraction, as well as increased contraction rate alone.
Methods
In study 1, twelve recreationally active male participants completed 3 trials in random order
consisting of 7x30second sprint cycles at 130%peak power output (PPO)(SIE), 60 minutes at
55% PPO (MICE), and a rest trial where no exercise was performed. In study 2 a separate
nineteen recreationally active male participants cycled for 1-hr at 55% PPO at either 65-rpm or
95-rpm. In study 3 a separate eighteen recreationally active males completed a replica study
similar to study 2 but with the addition of a 41minute submaximal trial at 95rpm at 55% PPO.
Indirect calorimetry was used to measure a number of metabolic variables during exercise.
Muscle biopsies were performed as part of study 1 and 3.
Results
Study 1: Significantly lower glycogen (94±24 vs 108±30 vs 125±31 mmol/kg/wt p=<.001) and
increased insulin sensitivity (0.28±0.05 vs 0.25±0.04 vs 0.22±0.04 GIR p=<0.05) were
observed 24 hours post SIE when compared to MICE. Study 2: Significantly greater
carbohydrate utilisation (2.48±0.2 vs 1.97±0.2g/min p=<.01) was observed when exercising at
95rpm vs 65rpm at 55%PPO. Study 3: Greater total glycogen use per contraction was observed
(-0.008±0.002 vs -0.006±0.002 mmol/kg/min p=<.05) at 95vs65rpm.
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Conclusions
There were no fibre specific differences in glycogen use between trials. Increased glycogen use
observed following SIE exercise is also observed following MICE at an increased contraction
rate. The increase in glycogen use was not shown to occur as a result of increased type 2 fibre
recruitment alone.