High Intensity Interval Training

Interval Training

• performance of repeated exercise bouts with brief recovery periods between

  • duration and intensity of work interval varies based on goal

    • longer work intervals: greater involvement of aerobic energy production

    • shorter work intervals: greater anaerobic metabolism

• not limited to only aerobic exercise

  • body weight, plyometrics, resistance exercises

High Intensity Training (HIT)

• attempts to achieve total muscular failure within each muscle group

• difference between HIT & HIIT:

  • HIT: exercise is performed just once per muscle group

  • HIIT: exercise is performed a number of times within a workout

Moderate Intensity continuous training (MCIT)

constant steady state exercise is performed for an extended duration

High Intensity Interval training (HIIT)

submaximal efforts that elicit >90% of VO2 max or >75% of maximal power

sprint interval training (SIT)

all-out/supramaxial effort >100 VO2peak or maximal power

Components of HIIT

• begins with a warm-up

• several brief bouts of high-intensity exercise

  • each high intensity bout followed by a recovery period of rest OR exercise at a lower intensity

  • number of intervals is determined by the fitness of level of the individual

• ends with a cooldown

• variables included in a HIIT exercise prescription include AT LEAST:

  • type of exercise (I.e. running, cycling)

  • intensity and duration of intervals

  • number of intervals performed

Examples of types of HIIT and SIT

High Intensity Interval Resistance Training (HIIRT):

• lifting heavy loads with partial recovery within a single set and complete exhaustion after each set

• exercise is performed a number of times within a session

High Intensity Functional Training (HIFT)²:

• merges high-intensity exercise with functional (multi-joint) movements

• ex: crossfit

Repeated-Sprint training (RST):

• high number of sprints lasting less than 10 s interspersed with relatively shorter recoveries (<60s) compared to the recovery periods of SIT

Examples of Interval Training Protocols

• alternating vigorous to supramaximal intensity for duration of 20-240 seconds with light to moderate intensity for duration of 60-360 seconds

• detrained individuals: alternating periods of brisk walking with walking at reduced pace

Example of Classifying HIIT Components

• interval length

  • long-interval (Li-HIIT)

  • moderate-interval (Mi-HIIT)

  • short-interval (Si-HITT)

  • Sprint interval (SIT)

  • repeated-spring exercise (RST)

• Volume

  • high volume (HV-HIIT

  • Moderate volume (MV-HIIT)

  • Low volume (LV-HIIT)

• Length of Training:

  • long term (LT-HIIT)

  • moderate term (MT-HIIT)
    Short term (ST-HIIT)

Effects of HIIT Protocols

results from meta-analysis of randomized control trials by Wen and colleagues:

• short intervals(<30 seconds), low volume <5 minutes, and short-term <4 weeks represent effective and time-efficient strategies for developing VO2max for the general population

• Long interval >2 min, high volume >15 minutes, moderate to long-term >4-12 weeks are recommended to maximize training effects

HIIT Training Responses: Short-term HIIT <12 weeks

• improved in overweight/obese populations:

  • VO2max

  • DBP

  • fasting BG

• improved in normal weight population: VO2max

HIIT demonstrated no effect on insulin, lipid profile, C reactive protein or interleukin 6 in overweight/obese population

HIIT Training Responses: Long-term HIIT >12 weeks

• improved in overweight obese population:

  • waist circumference

  • % body fat

  • VO2max

  • RHR

  • SBP and DBP

• Improved in normal weight population: VO2max

HIIT demonstrated no effect on insulin, lipid profile, C reactive protein or interleukin 6 in overweight/obese population

HIIT & SIT Training responses

• both are associated with classic physiological adaptations associated with MICT despite differences in training volume

  • increased aerobic capacity (VO2 max) and mitochondrial content

• limited evidence suggests increase in mitochondrial content is superior after HIIT compared to MICT

• less evidence available regarding the role to exercise intensity in mediating changes in:

  • skeletal muscle capillary density

  • maximum stroke volume

  • maximum cardiac output

  • blood volume

Health benefits of HIIT

• associated with similar physiologic adaptations to MICT

• exercise protocols of 5 days to 12 months show

  • improvements in:

    • VO2 max

    • resting metabolic rate

    • substrate metabolism

    • body composition

    • insulin sensitivity

    • cognitive function

  • decreased risk for:

    • CVD

    • breast cancer

    • OA
      RA

    • metabolic syndrome

Health Benefits of HIT & HIIT

• overall benefits of HIT

  • lower blood pressure

  • lower LDL and higher HDL

  • lower body fat

  • increased muscle mass

• specific benefits of HIIT

  • increased aerobic and anaerobic fitness levels

  • lower blood pressure

  • lower abdominal fat

  • weight loss with maintained muscle mass

  • increased insulin sensitivity

HIIT and Improved Vascular Function

• HIIT prescription of 4 intervals of 4 minutes (4×4 HIIT)

  • frequency: 3x/week

  • intensity:

    • work: 85-95% of HRmax/peak

    • rest: 60-70% of HRmax/peak

  • Time:

    • work: 4 minutes

    • rest: 3 minutes

  • Duration: 12-16 weeks

• Results:

  • FMD improved

    • 4.31% with HIIT

    • 2.15% with MCIT

  • HIIT had a greater tendency than MICT to induce positive effects on secondary outcomes including:

    • CRF

    • traditional CVD risk factors

    • oxidative stress

    • inflammation

    • insulin sensitivity

  • HIIT was more effective at improving brachial artery vascular function vs MICT

HIIT: Potenital Clinical Applications

• ACSM has considerations for application of HITT in individuals with the following diagnoses/clinical settings:

  • cardiac rehabilitation

  • heart failure

  • cardiac transplant

  • diabetes mellitus

  • spinal cord injury

  • ADHD

  • down sydrome