Table 1.

HIIT induced adaptive response on humans.

Reference	Population characteristics (n, M/F, age, $\dot{\text{V}}$O2max)	Training period	Exercise details	Main physiological and molecular changes
47	6, 6/0, 25 ± 2.9 yr, 55.5 ± 1.3 mL/kg/min	Single bout, cycling	HIIT: ∼40–45 min 2 min at 90% and 2 min at 25% $\dot{\text{V}}$O2peak.MICT: ∼60 min of at 50% $\dot{\text{V}}$O2peak.	Postprandial fat oxidation was increased similarly in both exercise groups with a higher increase in HIIT.
116	10, 10/0, 20 ±1yr., 52 ± 7 mL/kg/min	Single bout, running	HIIT: 3-min bouts at 90% $\dot{\text{V}}$O2maxand 3-min at 50% $\dot{\text{V}}$O2max. MICT: 50 min at 70% $\dot{\text{V}}$O2max.	Heart rate, RPE, and blood lactate was significantly higher in HIIT compared with MICT. Phosphorylation of AMPK Thr172 and p38MAPK Thr180/Tyr182 increased after exercise with no difference between exercise protocols. Muscle (vastus lateralis) PGC-1α mRNA content increased after hrs. of exercise with no difference between protocols. PGC-1α protein content was not changed at any time during the HIIT or MICT trials.
24	10, 10/0, 33.2 ± 6.7yr., 4.8 ± 0.3 L/min (∼61 mL/kg/min)	Single bout, cycling	HIIT: 10 × 4 min cycling at 81.6 ± 3.7% $\dot{\text{V}}$O2max and 2 min with at 50 W (11.4 0.9% peak power output). MICT: cycling at 65% $\dot{\text{V}}$O2max for a time corresponds to total HIIT work.	Plasma lactate, adrenocorticotrophic hormone, cortisol, and growth hormone were all higher immediately after HIIE vs. MICT. Plasma norepinephrine and interleukin-6 increased similarly. Plasma insulin decreased during recovery in both HIIE and MICE.
117	44,0/44, ∼25yr.,∼29 mL/kg/min	3 times a week for 16 weeks, running/walking	HIIT: 40 min with 1 min at 80–90% $\dot{\text{V}}$O2max and 2 min at 50–60% $\dot{\text{V}}$O2max. MICT: 40 min at 60–70% $\dot{\text{V}}$O2max.	HIIT was superior in improving norepinephrine, endothelin-1 (ET-1) and (nitrite/nitrate) NOx response to exercise than MICT. HIIT and MICT were similarly effective in improving ABP and insulin sensitivity. HIIT was superior in improving cardiorespiratory fitness.
118	16, 0/16, HIIT: 20 ± 1 yr. MICT: 19 ± 1 yr, HIT: 43.7 ± 6.8 mL/min/kg, MICT: 42.1 ± 7.2 mL/min/kg	5 weeks 3 days per week, cycling	HIIT: 120% (week 1), 130% (weeks 2 and 3) and 140% (weeks 4 and 5) of the lactate threshold, 2 min duration, with 1 min recovery. MICT: 80% (week 1), 90% (weeks 2 and 3) and 95% (weeks 4 and 5) of the lactate threshold. Work matched to HIIT.	In HIIT group there was a significantly greater improvement in vastus lateralis muscle buffer capacity (βm in vitro) than the MICT group. $\dot{\text{V}}$O2peak increased in both group similarly.
119	40, 40/0, 24.6 ± 3.8 yr, ∼55–60 mL/min/kg	8 weeks 3 days per week, running	HIIT: 4 × 4 min at 90–95% HRmax with 3min active recovery at 70% HRmax. SIT: 47 × 15-s at 90–95% HRmax with 15 s active recovery at 70% HRmax. MICT: at 70% HRmax for 45 min.	After HIIT and SIT $\dot{\text{V}}$O2max and stroke volume increased significantly
120	43, 17/26, 55–79 yr, ∼23,1–25,9 mL/min/kg	8 weeks 4 days per week, all-extremity ergometer	HIIT: 4 × 4 min at 85–95% HRpeak with 3 min active recovery at 65–75% HRpeak. MICT: 32 min at 65–75% HRpeak.	$\dot{\text{V}}$O2peak, ejection fraction and insulin resistance (HOMA-IR) improved in HIIT.
46	10, 10/0, 23 ± 1 yr, 46 ± 2 mL/kg/min	2 week 6 session, One-leg cycling	HIIT: 4 × 5 min at 65% Wmax and 2.5 min recovery with 20% Wmax. MICT: 30 min with 50% Wmax	CS maximal activity and mass specific O2 flux oxidative phosphorilation capacities in HIIT vs. MICT. In whole muscle, the COXIV, NDUFA9 and mitofusin 2 (MFN2) increased similarly in both groups.
121	9,n.d.,20–28 yr, ∼25.7–61.3 mL/kg/min	7–8 week 3 days/week, cycling	HIIT: 5 × 4 min 2 min recovery, 101% of $\dot{\text{V}}$O2max matched by W. MICT: average 27 min, 79% of $\dot{\text{V}}$O2max.	$\dot{\text{V}}$O2max elevated only in the MICT group. SDH activity increased in both group, but no difference found in PFK levels.
122	26, 10/16, obese,41 ± 9 yr, ∼31–36.2 mL/kg/min	18 session 3/week, running	4HIIT: 4 × 4 min at 85%–95%HRmax with 3 min recovery at 70% HRmax. 1HIIT: 10 × 1 min 90% HRmax with active recovery time n.d. MICT: 45 min at 70% HRmax.	$\dot{\text{V}}$O2max increased in the 4HIIT group compared to the other two groups. Calculated stroke volume increased only in the 4HIIT group. Muscle CS activity and TTE (time to exhaustion) improved in all exercise group with a difference between 4HIIT and MICT in TTE.
123	17, 17/0, ∼24.6 ± 3 yr, 3046–3757 mL/min	8 week 3 day/week, cycling	HIIT: 10 × 2 min at 105% with 2min recovery. 1MICT: 55 min of continuous exercise at −50%. $\dot{\text{V}}$O2max; 2MICT: 35 min at 70% $\dot{\text{V}}$O2max;	$\dot{\text{V}}$O2max and maximal exercise ventilation (VEmax) increased in all protocol with a higher increase of VEmax in HIIT to other MICT groups.
124	13, 13/0, 19–25yr.,37–54 mL/kg/min	4 week 5 workout/leg/week, cycling	One leg SIT: 20–30 bouts of 40–50 s all out efforts with 60–90 s recovery. One leg MICT: 30–50 min at 75% of $\dot{\text{V}}$O2max	Muscle SDH activity increased in both exercise groups.