Table 4.

Intervention studies, examining the intra-individual effect of $\dot{\text{V}}$O_2max after initiating oral contraceptive.

Author(s), year,	n	Performance test	Oral contraceptive	EE	Progestin	Duration of OC use	Test phase	Results	Risk of bias
								$\dot{\text{V}}$O2max (ml/kg/min)
Bryner et al., 1996[25]	10	treadmill	mono-phasic	35 mcg	norethisterone 1 mg	first intake cycle	without OC: F (day of ovulation divided by two)	41.6 +/− 12.1	high (RoB2)
							with OC: third week (interpreted as active-pill phase)	41.0 +/− 12.4
Casazza et al., 2002 [28]	6	cycle ergometer	triphasic	35 mcg	norgestimatep2p0.18 mg−0.25 mg	4 months	without OC: F (day 4–8)	42.3 +/− 8.1a	moderate (NOS)
							with OC: active-pill phase	36.9 +/− 5.4a
Lebrun et al., 2003[26]	7	treadmill	triphasic	35 mcg	norethisterone 0.5 mg–1.0 mg	2 months	without OC: F (day 3–8)	54.7 +/− 4.3	some concerns (RoB2)
							with OC: active-pill phase	52.0 +/− 4.2
Nakamura & Nose-Ogura, 2021 [39]	10	cycle ergometer	mono-phasic	20 mcg	norethisterone 1 mg	3 months	without OC: F (day 4–8)	41.8 +/− 6.1	moderate (NOS)
							with OC: active-pill phase	41.1 +/− 5.3
Notelovitz et al., 1987 [38]	6	treadmill	mono-phasic	35 mcg	norethisteronep2p0.4 mg	6 months	without OC (phase not specified)	41.2 +/− 11.8	moderate (NOS)
							with OC (phase not specified)	38.4 +/− 9.4
Rickenlund et al., 2004 [37]	13a	treadmill	mono-phasic	30 mcg	levonorgestrel 150 mcg	10 months	without OC: F (day 1–5)	55.3 +/− 4.4	high (NOS)
							with OC: active-pill phase	55.6 +/− 3.1
	12b						without OC: F (day 1–5)	41.9 +/− 3.3
							with OC: active-pill phase	41.7 +/− 3.1

Note. Values are reported as means +/− SD. Rickenlund et al. [37] distinguished between athletes (a) and sedentary controls (b).

OC: oral contraceptive, EE: Ethinyl estradiol, F: follicular phase, n: number of participants, NOS: Newcastle-Ottawa Quality Assessment Scale, RoB2: Cochrane Collaboration's tool for assessing risk of bias.

^a$\dot{\text{V}}$ O_2peak was measured.