ET vs SIT

Methods of Weight Cutting

One of the most prominent adaptations to training is a change in skeletal muscle substrate metabolism. Often, endurance training (ET) when compared to high-intensity sprint interval training (SIT) is described to have a higher effect on muscle oxidative capacity, substrate utilization and endurance performance. This unique experiment was to compare changes in exercise capacity and molecular and cellular adaptations in skeletal muscle after low-volume SIT and high-volume ET which had never been done before.

The protocol taken up in the experiment was to recruit sixteen healthy men from McMaster University who generally took up recreational exercise, two to three weeks prior to the experiment. None of the men were engaged in regular sport specific training. The men were randomly separated into two groups to undergo SIT and ET training respectively.

Pre-Experimental Procedures
To acclimatise the subjects to the experimental procedures of training and testing, several pre-experimental procedures were taken up. These included the following:

1. Subjects were made familiar with the laboratory in order to become orientated with the testing procedures and training devices.
2. During one of these visits, subjects performed an incremental test to exhaustion on an electronically braked cycle in order to determine VO2 peak using an online gas collection system.
3. All subjects also performed a 50kJ time trial and 750kJ time trial in order to become familiarized with the exercise tests employed during the main experimental trials. In a time trial subjects were instructed to complete 50 and 750 kJ self-paced laboratory time trials on an electronically braked cycle ergometer as quickly as possible with no temporal, verbal or physiological feedback. The only feedback provided during the time trials was presented as ‘distance covered’ on a computer monitor. In the experiment, 50 kJ was equated to 2 km, and 750 kJ was equated to 30 km. Exercise duration and average power were recorded upon completion of each test
4. Subjects in the SIT group also performed a familiarization Wingate test, and subjects in the ET group performed a submaximal exercise test to determine the workload that elicited ∼65% VO2 peak. A Wingate test is a test wherein Subjects in the SIT group completed a 30s maximal effort on an electronically braked cycle ergometer at a resistance equivalent to 7.5% of their body mass. The ergometer was interfaced with a computer containing software that applied the appropriate load for each subject. Subjects were instructed to begin pedalling as fast as possible ∼2 s before the computer applied the load and received extensive verbal encouragement throughout the test. Peak power, mean power and fatigue index were calculated and recorded by an online data acquisition system.
Note: All exercise tests performed during the familiarization period were performed on days separated by at least 24 h, and at least 3 days prior to baseline testing.

Experimental protocol
The experimental protocol consisted of:

• Baseline testing
• Two-week training intervention
• Post-training procedures.

Baseline Testing

Prior to training, all subjects underwent a resting needle muscle biopsy procedure. Here, a tissue sample from the vastus lateralis muscle was obtained. The muscle sample was immediately frozen in liquid nitrogen after removal from the leg. After this, two performance tests were taken up by all sixteen subjects. This was a 50kJ time trial an hour after the procedure and another 750kJ time trial two days after the procedure.

Training (Two Days After the 750kJ Time Trial)

This consisted of six sessions spread over 14 days, including 1 or 2 days recovery between training sessions. Both groups performed training on Mondays, Wednesdays and Fridays for 2 weeks.

• For the SIT group, training consisted of repeated 30 s maximal cycling efforts, interspersed with 4 min of recovery. The training progressed by increasing the number of repeats from four repetitions during sessions 1 and 2, to five repetitions during sessions 3 and 4, and finally to six repetitions during sessions 5 and 6.
• For the ET group, training consisted of 90–120 min of continuous cycling. Training progressed by increasing the duration of exercise from 90 min during sessions 1 and 2, to 105 min during sessions 3 and 4, and finally to 120 min during sessions 5 and 6.

Post-Training Procedures

The nature and timing of the post-training tests was the same as the pre-training procedures. During the experiments, subjects were allowed to continue their normal dietary and physical activity practices throughout the experiment, however, they were instructed to refrain from any exercise aside from activities of daily living and were even instructed to consume the same types and quantities of food for two days prior to the biopsy procedures and exercise performance tests. Subjects completed food diaries prior to the baseline biopsy and performance tests. They were replicated before the post training procedures.

On the muscle tissue the following tests were conducted:

• The maximal activity of cytochrome c oxidase (COX) was determined on a spectrophotometer.
• Protein content of the muscle homogenate was determined.
• Enzyme activity was calculated in mol (kg protein) −1 h−1.
• The amounts of COX subunit II (mitochondrial encoded) and COX subunit IV (nuclear encoded) were quantified using Western blotting.
• Total RNA was extracted from wet muscle and converted to cDNA
• The in vitro method of determining Muscle Buffering Capacity was taken up. This was calculated in μmol H+ (g dry muscle) −1 pH unit−1.
• Muscle glycogen was also measured

Findings
When muscle oxidative capacity and muscle buffering capacity were analysed, these tests were made to analyse exercise tolerance. The results from these studies were equivocal, and reported similar increases in the maximal activities of mitochondrial enzymes after interval and continuous training.

Training was seen to induce an increase in the maximal activity of COX and the protein contents of COX subunits II and IV, but there were no differences between groups despite the marked differences in training volume. However, with the increase in the content of these proteins that showed an increase in the number of mitochondria, there was no increase in the mRNA content in the muscle.

To conclude, the present study took two very diverse forms of training and reported that they induced remarkably similar changes in exercise capacity and selected muscle adaptations that are related to exercise tolerance. The SIT group took up markedly lower training volume and the results suggest that intense interval training is indeed a time-efficient strategy to induce rapid muscle and performance adaptations comparable to traditional endurance training.

Note that the article discusses that additional research would be necessary to clarify the effect of different acute exercise ‘impulses’ on molecular signalling events in the human skeletal muscle, and the precise time course and mechanisms responsible for the contraction-induced changes that facilitate the training adaptation. These were some events that were not analysed in the article.

What do you think the analysis would result in?