@Article{Schmidt2026,
journal="Biology of Sport",
issn="0860-021X",
year="2026",
title="The overload loop: a distinct reoxygenation pattern above the second ventilatory threshold revealed by a new analytical method",
abstract="Overpacing	is	frequently	observed	in	high-intensity	functional	training	modalities	such	as	CrossFit,	where	athletes	exceed	sustainable	intensity	domains	early	and	subsequently	fail	to	recover	performance	within	the	same	exercise	bout.	This	study	examined	whether	exercising	above	the	second	ventilatory	threshold	(VT2)	induces	distinct	reoxygenation	patterns	in	active	and	inactive	muscles	and	aimed	to	develop	a mathematical	method	for	quantifying	these	intensity-dependent	effects.	Fifty-four	healthy	men	performed	two	incremental	cycling	tests,	one	above	and	one	below	VT2,	while	SmO2 of	the	vastus	lateralis	and	triceps	brachii	was	continuously	measured.	Heart	rate	served	as	a systemic	reference	to	align	local	SmO 2  values,	yielding	the	new	metric	 MUSCLE SmO 2 /HRrel ,	defined	as	the	largest	exercise-to-recovery	difference	at	identical	relative	heart	rates.	Brachial	artery	diameter	was	additionally	assessed	in	a subsample.	Only	above	VT2 did	the	inactive	muscle	continue	to	deoxygenate into early recovery, whereas the active muscle reoxygenated immediately. When plotting both muscles	against	each	other,	this	produced	a distinct	circular	overload	loop,	not	observed	below	VT2.	 MUSCLE SmO 2 /HRrel  confirmed	this	asymmetry	statistically,	showing	a large	effect	in	the	triceps	brachii	(p < 0.001)	and	no	meaningful	difference	in	the	vastus	lateralis.	Above	VT2,	brachial	artery	diameter	decreased	and	subsequently	increased	during	recovery,	supporting	intensity-dependent	vascular	regulation.	Exceeding	VT2 triggers	an	asynchronous	reoxygenation	response	between	muscle	groups.	The	overload	loop	and	its	quantification	using	the	newly	developed	metric	provide	a novel	tool	for	analyzing	intensity-driven	SmO2 dynamics	and	offer	new	insight	into	the coordination of local and systemic vascular regulation under conditions of unsustainable exercise intensity.",
author="Schmidt, Annette
and Koch, Lucas
and Brandt, Tom
and Schinköthe, Timo",
pages="921--931",
doi="10.5114/biolsport.2026.159557",
url="http://dx.doi.org/10.5114/biolsport.2026.159557"
}