Last weekend I had the pleasure of giving two talks at the Sunshine Coast Fitness Summit. My only regret was that I didn’t get enough time to take in the scenery of the local area. I was fortunate enough to stay with legendary strength expert Mark McKean and his family, who again took me to my favourite Indian Restaurant on the coast for the buffet! A big thank you to the McKean family for looking after me and for Julie at the Sunshine Coast TAFE for bringing me up and running such a great conference.
Below is a brief summary of my talk on interval training, entitled Interval Training: An Efficient Tool For Improving Physical Capacity, Health & Fat Loss. I’ve included most of the information that was not in the notes for the delegates.
01. CLASSIFICATIONS
• Supramaximal Intervals = less than 2 minutes (‘all-out’ effort)
• Maximal Intervals = 2-10 minute intervals (close to maximum effort)
• Submaximal Intervals = greater than 10 minute intervals (anaerobic threshold pace)
02. THE FOUR DISTINCT ENERGY SYSTEMS
System 1:
Duration: up to 6 seconds
Primary Energy System: Phosphagen
Principal Fuel: ATP & CP
System 2:
Duration: 6 to 30 seconds
Primary Power System: Phosphagen & anaerobic glycolytic
Principal Fuel: ATP, CP & muscle glycogen
System 3(a):
Duration: 2 to15 minutes
Primary Power System: anaerobic glycolytic & aerobic glycolytic
Principal Fuel: Muscle glycogen & blood glucose
System 3(b):
Duration: 15 to 60 minutes
Primary Power System: aerobic glycolytic
Principal Fuel: Muscle glycogen & blood glucose
System 3(c):
Duration: 60 to 90 minutes
Primary Power System: aerobic glycolytic
Principal Fuel: Muscle glycogen, blood glucose & intra-muscular triglyceride
System 4:
Duration: longer than 90 minutes
Primary Power System: aerobic glycolytic & aerobic lipolytic
Principal Fuel: Muscle glycogen, blood glucose, intra and extra muscular triglycerides
03. INTERVAL TRAINING & PERFORMANCE
Endurance performance between 30 seconds and 2 minutes duration is enhanced most by supramaximal intervals (~4%).
Endurance performance over 2 minutes duration is enhanced most by intervals of maximal and supramaximal intensities (~6%).
The protocol used in research that has improved performance the most was 8 x 4-5 minutes with 6-90 seconds rest for 6 sessions, which improved 40-km cycling time trial between 4.6-8.3%.
MSSE 28:1427-1434. 1996
Eur. J. Appl. Physiol. 75:298-304. 1997
MSSE 31:736-741. 1999
Sportscience 8: 25-40. 2004
03. INTERVAL TRAINING & PERFORMANCE
Performance enhancement due to increased VO2max, lactate buffering ability and mitochondrial biogenesis.
MSSE 28:1427-1434. 1996
Eur. J. Appl. Physiol. 75:298-304. 1997
MSSE 31:736-741. 1999
04. INTERVAL TRAINING & HEALTH
Interval training has been shown to improve health & fitness in patients with coronary artery disease.
Eur. J. Cardiovasc. Prev. Rehabil. 11:216-222. 2004
Am. J. Cardiol. 95: 1080-1084. 2005
Epidemiological data shows that vigorous exercise is more protective against premature cardiovascular death than moderate-intensity exercise.
JAMA. 288: 1994-2000. 2002.
Eur. J. Cardiovasc. Prev. Rehabil. 13:798-804. 2006.
Interval training has been shown to improve health & fitness in patients with coronary artery disease and interval training is more effective than moderate-intensity exercise.
Eur. J. Cardiovasc. Prev. Rehabil. 11:216-222. 2004
Am. J. Cardiol. 95: 1080-1084. 2005
Scand. Cardiovasc. J. 42: 110-7. 2008
Exercise induces hypertrophy of the cardiomyocyte but the largest increases occur in response to interval training compared to moderate intensity exercise.
Cardiovasc. Res. 67: 16172. 2005
Interval training improves VO2max, stroke volume and left ventricular mass and contractility better than isocaloric programs at lower exercise intensity but longer duration.
MSSE. 39:665-71. 2007.
Heart failure patients improve VO2max and LV function better than moderate-intensity continuous training matched for the same caloric expenditure
Circulation. 115:3086-94. 2007.
Despite a small number of studies, more work is needed to address safety with at risk populations
ESSR. 37(3):139-146. 2009.
A leading research group has recently stated: “we have approximately 2000 hours with interval training in our laboratory in various patient groups, including heart failure, metabolic syndrome, coronary artery disease and hypertension, without any negative outcome.”
ESSR. 37(3):139-146. 2009.
05. THE EFFECTS OF INTERVAL TRAINING ON FAT LOSS
Interval training increases energy expenditure.
If energy expenditure exceeds energy intake over weeks and months then fat oxidation predominates and weight loss will follow.
Interval training increase the reliance on fat oxidation during continuous exercise sessions.
Two weeks (7- sessions) of 10 x 4-minutes resting 2 minutes increased fat oxidation 36% during a submaximal 60 minute cycling trial.
J. Appl. Physiol. 102: 1439-1447. 2007
An acute interval session increases insulin-independent glucose transport which lasts 1-3 hours after exercise ends
ESSR 36(2):58-63. 2008
Interval training improves insulin-mediated glucose uptake lasting 3-48 hours post exercise
ESSR 36(2): 58-63. 2008
Interval training increases insulin sensitivity and lowers fasting insulin
ESSR 37(2): 93-101. 2009
Interval training decreases fasting blood glucose and post prandial glucose
Nutrition 20(7-8): 716-27. 2004
Interval training decreases triglycerides and post prandial lipemia
Int. J. Obes. Relat. Metab. Disord. 28(6): 759-65. 2004.
The effects on insulin sensitivity and post prandial lipemia are immediate after exercise and persist 24-48 hours after training
Nutrition 20(7-8): 716-27. 2004.
Increases in whole body fat oxidation during exercise occur within 6-7 session or 2-3 weeks
JAP 102: 1439-1447. 2007.
Improvements are lost with 2 weeks of inactivity.
Appl. Physiol. Nutr. Metab. 34:411-419. 2009
Interval training improves glycogen storage similar to endurance training;
ESSR 36(2): 58-63. 2008.
Interval training increases fatty acid oxidation at rest, providing a negative energy balance is created
ESSR 37(2):93-101. 2009.
Am. J. Physiol. 273(3):E623-9. 1997.
Interval training - and exercise in general - does improve fat metabolism in muscle but does not increase 24-hour fat oxidation if an energy deficit is not created.
ESSR 37(2): 93-101. 2009
Interval training increases NO and reduces blood pressure chronically and acutely.
ACSM position stand
Interval training increases HDL-C and decreases LDL-C and TG levels
ACSM Position Stand 2009
Interval training increases mitochondrial enzymes involved in glucose (citrate synthase) and fat oxidation (bHAD) increasing the amount of fat oxidized during submaximal exercise.
JAP 102: 1439-1447. 2007.
Interval training increases signalling proteins involved in mitochondrial biogenesis to a similar extent that endurance training does
AMPK, p38MAPK, PGC-1α
Appl. Physiol. Nutr. Metab 34: 428-432. 2009
TWICE A DAY TRAININGINTERVAL TRAINING & FAT LOSS
Performing interval training with low muscle glycogen stores - such as performing two training sessions a day or during periods of carbohydrate restriction increases mitochondrial enzymes involved in carbohydrate and fat oxidation and increase whole body fat oxidation during submaximal exercise better than once a day training or training with normal glycogen stores.
JAP. 105: 1462-1470. 2008
In the study cited above, 7 subjects cycled 100 minutes steady state one day and performed interval training the next (8 x 5-min) six days per week for a 3-week period.
Another 7 subjects cycled 100 minutes steady state then performed the interval session 1-2 hours later. The next day was a rest day. The day ‘on’, day ‘off’ lasted 3 weeks.
Training twice per day increased resting muscle glycogen content, mitochondrial enzymes involved in the TCA cycle (citrate synthase), β oxidation (β HAD), electron transport chain activity (COX sub units) and rates of whole body fat oxidation during submaximal exercise more than training daily for 3 weeks.
INTERVAL TRAINING VS STRENGTH TRAINING
What’s the difference?
Strength training induces the PI3-k-mTOR complex cascade to increase protein synthesis and muscle cell growth.
Appl. Physiol. Nutr. Metab 34:403-410. 2009
ENDURANCE TRAINING
Endurance training induces increases the AMPK, p38MAPK, PGC-1α pathway which results in increased mitochondrial density and oxidative enzyme activity, termed mitochondrial biogenesis.
INTERVAL TRAINING
Although performed in a similar fashion to strength training - brief bouts of intense exercise with recovery periods in between
Interval training stimulates the AMPK-PGC-1α pathway and not the mTOR pathway in the 4-8 hours post training that result in increased mitochondrial biogenesis.
Appl. Physiol. Nutr. Metab 34:428-432. 2009
INTERVAL TRAINING VS STRENGTH TRAINING
Are they incompatible?
If performed in the same session, aerobic adaptation is unaffected but strength adaptation is negatively effected.
But if performed on separated days or 8 hours apart, then the answer is strength and interval training are not incompatible
Appl. Physiol. Nutr. Metab 34:355-361. 2009
