Table 1

Study characteristics of the studies that achieved synthesis

Study	Year	Design	Sample size	Patient characteristics	Intervention	Exercise protocol (modality, intensity, volume, frequency)	Intervention period	Comparison type	Primary endpoint	Secondary endpoint	Response criteria
Weatherwax56 65	2018	RCT	39	Male and female. Less than 30 min activity in 3 days per week. 30–75 years old.	HIIT	Stationary bike, elliptical machine or treadmill. Stepwise progression in intensity depending on exercise group.	12 weeks	Standardised vs Individualised	VO_2max	Physical activity, sitting time, HRrest, HRmax, body measurement parameters, dietary intake	VO_2max Δ>ME (4.7%)
Sisson49	2009	RCT	310	Female only (post-menopausal). Sedentary. 45–75 years old. Multiple ethnicities.	END	Recumbent cycle ergonometer or treadmill (alternating); 50% baseline VO_2max, 3–4 sessions/week	24 weeks	4 vs 8 vs 12 kcal/kg/week	VO_2max	N/A	VO_2max Δ>0%
Earnest50	2011	RCT	251	Female only (postmenopausal). Sedentary. 45–75 years old. Caucasian only.	END	Recumbent cycle ergonometer or treadmill (alternating); 50% baseline VO_2max, 3–4 sessions/week	24 weeks	Control vs 4 vs 8 vs 12 kcal/kg/week	VO_2max	N/A	VO_2max Δ>0%
Pandley30	2015	RCT	202	Male and female. T2DM. 30–75 years old.	END	Treadmill; 50%–80% VO_2max, 3 session/week	36 weeks	Control vs END vs RET vs both	VO_2max	HbA1c, body measurement parameters, systolic and diastolic blood pressure (at rest), systolic blood pressure (peak), HRrest, RER, insulin use	VO_2max = Δ>5%
Pandley30	2015	RCT	202	Male and female. T2DM. 30–75 years old.	RET	Full body training, compound movements (upper, lower, abdominal); 10–12 repetition range, 3 sessions/week	36 weeks	Control vs END vs RET vs both	VO_2max		VO_2max = Δ>5%
Montero28	2017	RCT	78	Male only. Sedentary. Healthy. 18–35 years old.	END, HIIT, mixed	Recumbent cycle ergonometer; average of 65% of Wmax (between four intensity profiles), range from 1 to 5 sessions/week	6 weeks	Exercise frequency (1 vs 2 vs 3 vs 4 vs 5 sessions/week)	VO_2max, W_max	Haemoglobin mass, plasma volume, red blood cell volume, blood volume, body measurement parameters, mitochondrial volume density	VO_2max & W_max =>1 T.E.
Bonafiglia27	2016	RCT (cross-over)	21	Male and female. Recreationally active only. Age range not stated.	END	30 min cycling at 65% of VO_2max, 4 sessions/week	3 weeks x 2	END vs HIIT	VO_2max	Lactate threshold, HR_submax, W_max	all parameters =>2 S.E.
Bonafiglia27	2016	RCT (cross-over)	21		HIIT	Eight blocks of 170% of VO_2max (20 s activity, 10 s rest), 4 sessions/week	3 weeks x 2	END vs HIIT	VO_2max	Lactate threshold, HR_submax, W_max	all parameters =>2 S.E.
Ross48	2015	RCT	121	Male and female. Sedentary. Average age 53.2.	LALI	180-300kcal at 50% of VO_2max per session, 5 sessions/week	24 weeks	LALI vs HALI vs HAHI at 4, 8, 16 and 24 week intervals	VO_2max	N/A	VO_2max =>1 T.E.
					HALI	360-600kcal at 50% of VO_2max per session, 5 sessions/week
					HAHI	360–600 kcal at 75% of VO_2max per session, 5 sessions/week
Gurd42	2016	RCT	63	Healthy males who had previously attended prior, similar studies.	HIIT	Synthesis of five HIIT studies, each with differing methods.	4–6 weeks	HIIT vs control	VO_2max	Lactate threshold, time to completion	VO_2max =>2 T.E.
Yan51	2017	Cohort	39	Male only. Moderately-trained. 18–45 years old. Caucasian only. BMI <30 kg/m².	HIIT	Variable intensity tailored to individual’s preintervention measures, 3 HIIT sessions/week	4 weeks	N/A (no control/ comparison)	VO_2max	Lactate threshold, power output, distance	VO_2max Δ>0%
Scharhag-Rosenberger57	2012	Cohort	18	Male and female. 32–50 years old. BMI 19–28 kg/m².	END	Jogging or walking, 45 min duration at intensity of 60% hour or HR at lactate threshold, 3 sessions/week	50 weeks	N/A (no control/ comparison)	VO_2max	Lactate threshold, resting heart rate, submaximal heart rate	Variable; VO_2max = Δ>5.6%
Higgins58 67	2015	Cohort	23	No population data provided in detail.	HIIT	Cycling. 3 sessions/week	6 weeks	N/A (no control/ comparison)	VO_2max	Glucose, systolic blood pressure, diastolic blood pressure, lipid profile	VO_2max =>2 s.E.
Astorino29	2018	Cohort	14	Male and female. Healthy. Previously active (150 minute/week). 20–49 years old.	HIIT	Eight to 10 1 min rounds of HIIT, 130% of power output based on volunteer ventilatory threshold, 3 session/week	3 weeks	control vs HIIT	VO_2max	Time trial performance, ventilatory threshold	VO_2max ≥2 s.E.
Kohrt26	1991	Cohort	320	Male and female. Healthy. Untrained. 60–71 years old.	END	Up to 50 minutes/day, 85% of HR_max graded increase in volume and intensity up to third month, daily exercise	36–52 weeks	Control vs END	VO_2max	RER_max, VE_max, HR_max, HR_rest	None
Nybo18	2010	Cohort	36	Male only. Untrained. No training in prior 2 years. 20–43 years old.	HIIT	Running. 20 min total exercise duration. Five sets of 2 min at above 95% of calculated HR_max two sessions/week	12 weeks	HIIT vs END vs RET vs control	VO_2max	HR_rest, BP_rest, HR_max	None
					END	Treadmill. 60 min at 80% of HR_max 2.5 sessions/week
					RET	Lower body compound and isolation exercises, 3–4 sets per exercise, 1 min rest interval, average duration 60 min, 2 sessions/week
Osei-Tutu & Campagna59	2004	RCT	40	Male and female. Healthy. Sedentary. 20–40 years old.	END	‘Long Bout’ modality considered: 30 minutes/day, 60%–79% HR_max five sessions/week	8 weeks	‘Long bout’ (END) vs ‘short bout’ vs control	VO_2max	N/A	None
Trapp60	2008	RCT	45	Female only. Healthy. Inactive. 18–30 years old. Mixed ethnicity.	HIIT	Ergometer. 8s sprinting, 12s recovery. Maximum of 60 bouts per session. Up to 20 min/session. 45 total exercise sessions in intervention period.	15 weeks	HIIT vs END vs control	VO_2max	Body fat and muscle comparisons	None
Trapp60	2008	RCT	45		END	Ergometer. Exercise at 60% VO_2max. Up to 40 min exercise per session.	15 weeks	HIIT vs END vs control	VO_2max	Body fat and muscle comparisons	None
Metcalfe61	2012	RCT	29	Male and female. Healthy. Sedentary. Range for intervention and control averages 19–26 years old.	HIIT	Ergometer, maximal pedalling against 7.5% volunteer bodyweight, 10 min duration, 3 sessions/week	6 weeks	HIIT vs control	VO_2max	N/A	None
Ziemann62	2011	RCT	21	Male only. Healthy. Inactive. College age.	HIIT	Six 90s maximal effort and 180s recovery rounds, set to 80% VO_2max, 3 sessions/week	6 weeks	HIIT vs control	VO_2max	Power output (multiple parameters)	None
Burgomaster63	2008	Cohort	20	Male and female. Healthy. Sedentary. No intense exercise for at least 1 year prior. Range for intervention and control averages 23–24 years old.	END	40–60 min cycling, 65% of VO_2max, 5 sessions/week	6 weeks	HIIT vs END	VO_2max	HR_max, RER	None
Burgomaster63	2008	Cohort	20		HIIT	30 s of 4–6 bouts (increasing count), maximum effort (Wingate test), 4.5 min recovery interval, 3 session/week	6 weeks	HIIT vs END	VO_2max	HR_max, RER	None
Lo53	2011	RCT	34	Male only. Healthy. Inactive. Average age 20.4 years old.	END	30 min treadmill, 70%–85% HR_max, 3 session/week	24 weeks	END vs RET	HR_max	N/A	None
Lo53	2011	RCT	34	Male only. Healthy. Inactive. Average age 20.4 years old.	RET	Ten exercises (full body, compound and isolation), incremental increase in intensity (weight), 3 session/week	24 weeks	END vs RET	HR_max	N/A	None
McKay64	2009	RCT	12	Male only. Healthy. Not previously in a formal training programme. Average age 25 years old.	END	90–120 min of 65% pretraining VO_2max. Permitted 60–90s intermittent recovery if required. 8 sessions total.	3 weeks	END vs HIIT	VO_2max	W_max, lactate threshold (multiple parameters)	None
McKay64	2009	RCT	12		HIIT	60s 120% W_max followed by 60 s recovery for 8–12 bouts, 8 sessions total	3 weeks	END vs HIIT	VO_2max	W_max, lactate threshold (multiple parameters)	None
Dunham65	2012	RCT	15	Male and female. Healthy. Physically active. Average age range 20.2–21.3 years old.	END	Ergometer, 45 min of 60%–70% VO_2max, 3 sessions/week	4 weeks	END vs HIIT	VO_2max	RER_max, HR_max	None
Dunham65	2012	RCT	15		HIIT	Ergometer, five bouts of 1 min at 90% VO_2max followed by 2 min recovery, 3 sessions/week	4 weeks	END vs HIIT	VO_2max	RER_max, HR_max	None
Macpherson66	2010	C	20	Male and female. Recreationally active only. Ages per groups 24.3±3.3 and 22.8±3.1.	END	Treadmill, continuous running, 30–60 min (progressive increase), at 65% VO_2max intensity, 3 sessions/week	6 weeks	END vs HIIT	VO_2max	Cardiac output, resting metabolic rate	None
Macpherson66	2010	C	20		HIIT	Treadmill, 30s maximal effort sprinting, 4 min recovery interval, increase in bout count from 4 to 6, 3 sessions/week	6 weeks	END vs HIIT	VO_2max	Cardiac output, resting metabolic rate	None
Shepherd67	2013	RCT	16	Male only. Sedentary. Healthy. Average age per groups 21±1 and 22±2.	END	Ergometer, 40–60 min per session (increasing volume during intervention), 65% VO_2max, 5 sessions/week.	6 weeks	END vs HIIT	Intramuscular triglyceride, perilipin	VO_2max, W_max, insulin and glucose	None
Shepherd67	2013	RCT	16		HIIT	Ergometer, 30 s maximal effort cycling, 4.5 min recovery interval with 30W resistance at 50 rpm pace, increase in bout count from 4 to 6, 3 sessions/week.	6 weeks	END vs HIIT	Intramuscular triglyceride, perilipin	VO_2max, W_max, insulin and glucose	None
Warburton54	2004	RCT	20	Male only. Active. Healthy. Average age per total group 29±4.	END	Ergometer, 30–48 min per session (increasing volume during intervention), 64.3%±3.7% VO_2max, 3 sessions/week.	12 weeks	END vs HIIT vs control	Blood volume constituents	VO_2max, HR_max, W_max, systolic and diastolic blood pressure	None
Warburton54	2004	RCT	20		HIIT	Ergometer, 2 min high effort (90% VO_2max) followed by 2 min low effort (40% VO_2max) for a number of bouts that would match the END equivalent in terms of total work output, 3 sessions/week.	12 weeks	END vs HIIT vs control	Blood volume constituents		None
Berger55	2006	C	23	Male and female. No intense exercise in preceding 2 years. Healthy. Average age per total group 24±5.	END	Ergometer, 30 min per session, intensity 60% VO_2max, 3–4 sessions/week	6 weeks	END vs HIIT vs control	VO_2max, time delay, primary amplitude, primary time constant	W_max, lactate threshold, HR_max	None
Berger55	2006	C	23		HIIT	Ergometer, 20 1 min bouts of 90% VO_2max followed by 1 min rest, 3–4 sessions/week	6 weeks	END vs HIIT vs control		W_max, lactate threshold, HR_max	None
Matsuo68	2013	RCT	42	Male only. Sedentary. Healthy. Average age in study 26.5±6.2.	END	Ergometer, 40 min, 60%–65% VO _2max, 60 rpm maintained, 5 sessions/week	8 weeks	END vs HIIT (‘sprint’) vs HIIT (‘HIAT’)	VO_2max, cardiac parameters (multiple)	Blood constituents	None
Matsuo68	2013	RCT	42		HIIT	‘sprint’; ergometer, 30 s 120% VO_2max >85 rpm followed by 15s rest period for seven rounds; ‘HIAT’; alternating between 3 min 80+% VO_2max at 70–80 rpm against 2 min 50% VO_2max at 60 rpm (cooldown at end for both); five sessions/week	8 weeks	END vs HIIT (‘sprint’) vs HIIT (‘HIAT’)	VO_2max, cardiac parameters (multiple)	Blood constituents	None
O'Donovan69	2005	RCT	42	Male only. Sedentary. Healthy. Age range 30–45 years old.	END (lo intensity)	Ergometer, 400 kcal at 60% VO_2max, 3 sessions/week	24 weeks	END (lower intensity) vs END (higher intensity) vs control	VO _2max	Lipid profile, fibrinogen	None
O'Donovan69	2005	RCT	42	Male only. Sedentary. Healthy. Age range 30–45 years old.	END (hi intensity)	Ergometer, 400kcal at 80% VO_2max, 3 sessions/week	24 weeks	END (lower intensity) vs END (higher intensity) vs control	VO _2max	Lipid profile, fibrinogen	None
Sandvei70	2012	RCT	23	Male and female. Sedentary to moderately trained. Healthy. Age range 18–35 years old.	END	Outdoor running, 30–60 weeks (5 min incremental increase per week), 70%–80% HRmax, 3 sessions/week	8 weeks	HIIT (sprint) vs END	Glucose, insulin	Lipid profile, HR_max, VO_2max	None
Sandvei70	2012	RCT	23		HIIT	Sprinting, 30 s maximal effort followed by 3 min recovery, 5–10 sprints (one incremental increase per week), 3 sessions/week	8 weeks	HIIT (sprint) vs END	Glucose, insulin	Lipid profile, HR_max, VO_2max	None
Hautala52	2005	RCT (crossover)	91	Male and female. Sedentary. Healthy. Average age in study 42±5.	RET	15 exercises including major muscle groups, 1 set of 8–12 repetitions to near fatigue. Resistance training every 2 days with a focus on arm or leg strength. 5 consecutive sessions/week	2 weeks	END vs RET vs control	BMI	VO_2max, HR_max, RER_max, maximum quadricep strength	VO_2max Δ>0%
Hautala52	2005	RCT (crossover)	91		END	40 min cycle ergometer, 5 consecutive sessions/week	2 weeks	END vs RET vs control	BMI	VO_2max, HR_max, RER_max, maximum quadricep strength	VO_2max Δ>0%

BMI, body mass index; END, endurance exercise training; HAHI, high amount, high intensity exercise; HALI, high amount, low intensity exercise; HIIT, high intensity interval training; HR_max, maximum heart rate; LALI, low amount, low intensity exercise; ME, measurement error; N/A, not available; RCT, randomised controlled trial; RER, respiratory exchange ratio; RET, resistance exercise training; T2DM, type 2 diabetes mellitus; VO_2max, maximal rate of oxygen consumption.