Research Review By Jessica Sleeth©

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Date Posted:

September 2011

Study Title:

Run sprint interval training improves aerobic performance but not maximal cardiac output

Authors:

Macpherson REK, Hazell TJ, Olver TD, Paterson DH, Lemon PWR

Author's Affiliations:

Exercise Nutrition Research Laboratory, Faculty of Health Sciences, School of Kinesiology & the Faculty of Health Sciences, Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada.

Publication Information:

Medicine & Science in Sports & Exercise 2011; 43(1): 115-122.

Background Information:

Endurance training (ET) is the traditional form of cardiovascular physical activity, yet recently sprint interval training (SIT) has become popular. ET typically requires 30-60 minutes of continuous cardiovascular activity several days per week. SIT consists of 4-6 rounds of ‘all out’ exercise, with rest intervals in between – the length of the effort and rest intervals varies. The popularity of SIT is due in large part to recent studies demonstrating that SIT produces similar gains in muscle and aerobic performance as ET, but in less time (1, 2).

Endurance training has been extensively studied in the past, with noted performance adaptations in both central (cardiac output) and peripheral (skeletal muscle arterial-venous oxygen difference) systems, which increases overall maximal oxygen uptake (VO2MAX) (2). In general, ET leads to greater exercise capacity, improved overall health, and a decrease in body mass (3). Sprint interval training positively affects both anaerobic and aerobic metabolism, which improves numerous athletic performance parameters, such as cycling time to exhaustion (4). Many athletes appear to benefit from SIT and researchers wonder whether the general adult population could benefit as well.

There are currently no best practices for mode, intensity, duration, and recovery for interval training programs. The majority of research has been conducted with cycling, yet the authors believe that determining best practices for running would be more applicable to a larger population and greater range of physical activities. ET is proven to significantly reduce body fat and improve cardiac output; while there is no available data on SIT and effects on body composition or cardiac output.

The purpose of this study is to determine whether SIT (running) will produce similar performance improvements as ET and to document any chronic effects on body mass, body composition, resting metabolic rate, run time trial performance, VO2MAX, maximal cardiac output, and maximal arterial-venous oxygen difference. The authors hypothesize that SIT running will result in similar performance adaptations as ET without affecting maximal cardiac output.

Pertinent Results:

Body Composition
There was no significant difference in body mass pre-training or post-training between and within ET and SIT groups. Fat mass decreased significantly by 12.4% and 5.8% in the SIT and ET groups, but there was no significant change between groups. The decrease in fat mass in the SIT group (P = 0.002) occurred in men, but not women, yet the decrease in the ET group (P = 0.002) occurred in both men and women. Lean mass increased by 1.0% (P = 0.037) in both groups, but there was no significant difference between groups.

Resting Metabolic Rate
There was no significant difference in resting metabolic rate (P = 0.479) pre-training or post-training within or between SIT and ET groups.

2000m Run Time Trial
The baseline 2000m run time trial was similar for both groups (approximately 9 minutes). Performance increased by 4.6% (-25.6 seconds) (P < 0.017) in the SIT group and 5.9% (-31.9 seconds) (P < 0.017) in the ET group. The increases were not significantly different between groups.

Anaerobic Performance

Peak power increased by 5.1% (P = 0.002), during the 30-second SIT bouts, from the first training session to the last. There was no significant difference in average speed over the 6-week training period.

VO2MAX
73% of subjects reached a VO2 plateau near the end of the test. The SIT group improved VO2MAX by 11.5% and the ET group improved by 12.5% (SIT & ET P < 0.001). The increases were not significantly different between groups.

Maximal Cardiac Output, Stroke Volume, and arterial-mixed venous difference
Cardiac output increased in the ET group by 9.5% or 2.1 L/min (P=0.01). Cardiac output did not significantly increase with SIT training. Heart rate max during the cardiac output testing was similar pre-training and post-training and between SIT and ET groups. In post-training testing, stroke volume increased 10.4% (P = 0.076) in the ET group; with no change in the SIT group. A significant interaction effect (group by time) occurred between groups for arterial-mixed venous difference; the SIT group increased 7.1% and the ET group decreased 7.1% (P < 0.045).

Compliance with Exercise Training
All subjects completed all exercise sessions, except for one subject from each group (total 5 missed sessions due to injuries).

Clinical Application & Conclusions:

As previously mentioned, this study is the first to examine the effects of chronic SIT on central and peripheral oxygen adaptations and the effects on body composition using running training instead of cycling. The results identify that SIT induces similar changes in body composition, performance, and VO2MAX as ET, but had no effect on maximal cardiac output.

Effect on Body Composition
Body composition changed in both SIT and ET groups. The SIT group lost 12.4% of total fat mass and the ET group lost 5.8% total fat mass. The results are similar to previous interval training studies where fat mass decreased with less intense, but longer interval training. The women in the SIT group did not lose fat mass, thus there may be a gender interaction factor with the training (however, there were only 4 women per group, thus further study is necessary). Both training groups gained a significant amount of lean mass (0.6kg for both SIT and ET groups). It is of importance that the fat losses of both groups are similar since the ET group trained 18 times longer during the 6-week period than the SIT group.

With the ET group, changes in body composition are likely due to the energy expenditure during training, however with the SIT group, intense interval training causes post-exercise oxygen consumption (EPOC, which is influenced more by exercise intensity than duration) that leads to negative post-exercise energy balance. This could increase overall lipid and energy expenditures with SIT. Intense interval training also increases beta oxidation and the transport of fat (within skeletal muscle cells and mitochondria). Additionally, SIT could influence chronic fat use, which may contribute to overall fat loss.

2000 m Run Time Trial
The baseline 2000m run time trial was similar for both groups (approximately 9 minutes). Performance increased by 4.6% (-25.6 seconds) (P < 0.017) in the SIT group and 5.9% (-31.9 seconds) (P < 0.017) in the ET group. The increases were not significantly different between groups.

Anaerobic Performance
Peak power increased by 5.1% (P=0.002), during the 30-second SIT bouts, from the first training session to the last. There was no significant difference in average speed over the 6-week training period.

VO2MAX
73% of subjects reached a VO2 plateau near the end of the test. The SIT group improved VO2MAX by 11.5% and the ET group improved by 12.5% (SIT & ET P < 0.001). The between-group differences were not significant.

Maximal Cardiac Output, Stroke Volume, and arterial-mixed venous difference
Cardiac output increased in the ET group by 9.5% or 2.1 L/min (P = 0.01). Cardiac output did not significantly increase with SIT training. Heart rate max during the cardiac output testing was similar pre-training and post-training and between SIT and ET groups. In post-training testing, stroke volume increased 10.4% (P = 0.076) in the ET group; with no change in the SIT group. A significant interaction effect (group by time) occurred between groups for arterial-mixed venous difference; the SIT group increased 7.1% and the ET group decreased 7.1% (P < 0.045).

Compliance with Exercise Training
All subjects completed all exercise sessions, except for one subject from each group (total 5 missed sessions due to injuries).

Study Methods:

Subjects:
  • 20 young, healthy recreationally active (11 ultimate Frisbee players, 9 university students) men (n=12) and women (n=8) volunteered to participate. None were systematically training before the study.
  • Procedures and potential risks were explained to all subjects prior to any testing. All subjects provided written informed consent.
  • Overall health and fitness were assessed using the Physical Activity Readiness Questionnaire.
  • Subjects were matched into the SIT or ET groups based on sex, time trial performance and VO2MAX.
  • Subjects were encouraged to maintain their pre-study physical activity and diet patterns throughout the testing and training period.
  • The study was approved by the University of Western Ontario Ethics Committee for Research on Human Subjects.
Study Design:
  • Subjects completed 6 weeks of ET or SIT training (3 sessions per week).
  • Before and after training, subjects were tested for: body composition, resting metabolic rate, VO2MAX, a maximal cardiac output, and a 2000m run time trial performance. Body composition was measured before the resting metabolic rate test or before the VO2MAX test on a single day. All other tests were separated by 24 hours.
  • Subjects refrained from alcohol, caffeine, and physical activity 2 hours before all training and testing sessions.
  • Recovery was standardized to allow 48 hours between the final training session and the post-testing.
  • Post-testing was completed in the same order for all subjects (body composition/resting metabolic rate/VO2MAX performance, and maximal cardiac output).
  • Prior to baseline testing, subjects were familiarized with all testing and training procedures to ensure any learning effect was minimized
Baseline Tests:
All exercise tests were performed on separate days (6 days of pre-testing and 4 days of post-testing) and were completed at least 2 days before training session. Testing consisted of 4 measures:

Body Composition: lean and fat body mass were determined by whole-body densitometry using air displacement via the BodPod (Life Measurements). Testing was conducted according to manufacturer’s instructions. Thoracic gas volume was estimated for all subjects using the predictive equation integral to the BodPod software. The obtained value for body density was used in the Siri equation to estimate body composition.

Resting metabolic rate: measured by indirect calorimetry using an online breath-by-breath gas collection system (Vmax Legacy) after a 12-hour overnight fast. The system was calibrated appropriately. Subjects limited their activity getting to the lab and rested supine for 30 minutes in an environmental chamber. All measurements were taken between 7am and 9am. The subjects were instructed to remain motionless and to avoid sleeping during the test. The average of the last 15 minutes of collection was used to estimate the fasting energy expenditure.

VO2MAX Test: subjects performed a 5-minute warm-up on the treadmill (Desmo Pro) at 5mph (8 kph) for the women and 6 mph (9.7 kph) for the men. Once warmed-up, subjects performed a progressive, continuous incremental speed test to determine VO2MAX and run velocity max. Oxygen consumption was collected continuously and analyzed by an online breath-by-breath gas collection system (Vmax Legacy). Heart rate was recorded with a Polar HR Monitor. The greatest 30-second average was taken as VO2MAX.

Maximal Cardiac Output: Subjects performed practice trials of the procedure at rest and at near-maximal exercise. The test involved continuous treadmill running (Trackmaster) at 90% of the speed that elicited VO2MAX until they could not continue. The duration was between 4 and 7 minutes. Oxygen consumption and HR were measured throughout the test to ensure the cardiac output was attained at or near VO2MAX.

Maximal Stroke Volume and arterial-mixed venous oxygen difference: Calculated using a derivative of the Fick equation (whole body VO2 is the product of maximal cardiac output and the arterial-mixed venous difference. Used values for heart rate max and VO2max from the cardiac output max test).

Performance Test (2000m run time trial): Subjects completed self-paced (as quickly as possible without feedback) 2000m run time trials on a 200m indoor track. Prior to recorded time trial, subjects completed 3 separate run time trials to minimize any learning effect on the timed trial. The mean of the 2 best time trials was recorded as the baseline test.

Training:
Training began approximately 48-hours following completion of baseline testing. The training program consisted of 3 sessions per week for 6 weeks (1-2 days recovery between sessions). Sessions were monitored in the lab.

Endurance Group:
Training progressed from 30 minutes in weeks 1 and 2; to 45 minutes in weeks 3 and 4; and to 60 minutes in weeks 5 and 6. Subjects trained at 65% VO2MAX on a treadmill.

Sprint Interval Group:
Subjects completed 30-seconds of maximal treadmill running effort with 4-minutes of active recovery. Training progressed from 4 sets in weeks 1 and 2; to 5 sets in weeks 3 and 4; to 6 sets in weeks 5 and 6.

Post-training Procedures:
Post-training procedures were identical to baseline testing and commenced 2-4 days after the final training sessions.

Statistical Analyses:
The authors used Sigma Stat for Windows (version 3.5, Systat Software Inc., Point Richmond, CA). Normality and variance homogeneity were tested, followed by two-way (treatment x times) repeated measures ANOVA to test significance between pre-training and post-training groups (when appropriate, used Tukey post hoc testing). Significance was obtained at P < 0.05. All results presented as means ± SEM.

Study Strengths / Weaknesses:

  • As noted when discussing the body composition results, the results may have been influenced by differences in gender (with respect to body composition and training adaptations). There were fewer women than men in the trial, which made it difficult to scientifically compare the differences between genders.
  • The strenuous nature of SIT could result in cardiovascular or musculoskeletal complications in older or less fit individuals. A proper warm-up prior to beginning SIT may improve anaerobic and aerobic power quickly and safely, however SIT training may not be appropriate for everyone.
  • The methods section indicates that the authors matched subjects into the SIT and ET groups based on sex, time trial performance, and VO2MAX. It is possible that the non-random allocation of subjects could have influenced the results.

Additional References:

  1. Burgomaster KA, Howarth KR. Phillips SM, et al. Similar metabolic adaptations during exercise after low volume sprint interval training and traditional endurance training. J Physiol. 2008;586:151-60.
  2. Gibala MJ, Little JP, van Essen M, et al. Short-term sprint interval versus traditional endurance training: Similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(5):901-11.
  3. Talanian JL, Galloway SD, Heigenhauser GJ, Bonen A, Spriet LL. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol. 2007;102:1439-47.
  4. Burgomaster KA, Hughes SC, Heigenhauser GJF, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Apply Physiol. 2005;98:1985-90.