ORIGINAL RESEARCH
published: 31 July 2018
doi: 10.3389/ phys.2018.01034
F on ie s in Physiology | www. on ie sin.o g 1July 2018 | Volume 9 | A icle 1034
Edi ed by:
Hassane Zouhal,
Uni e si y o Rennes 2 – Uppe
B i any, F ance
Re iewed by:
Daniel A. Kane,
S . F ancis Xa ie Uni e si y, Canada
Thie y Busso,
Uni e si y o Sain -E ienne, F ance
*Co espondence:
Ibai Ga cia-Taba
[email p o ec ed]
Special y sec ion:
This a icle was submi ed o
Exe cise Physiology,
a sec ion o he jou nal
F on ie s in Physiology
Recei ed: 22 May 2018
Accep ed: 11 July 2018
Published: 31 July 2018
Ci a ion:
Ga cia-Taba I and Go os iaga EM
(2018) A “Blood Rela ionship”
Be ween he O e looked Minimum
Lac a e Equi alen and Maximal
Lac a e S eady S a e in T ained
Runne s. Back o he Old Days?
F on . Physiol. 9:1034.
doi: 10.3389/ phys.2018.01034
A“Blood Rela ionship” Be ween he
O e looked Minimum Lac a e
Equi alen and Maximal Lac a e
S eady S a e in T ained Runne s.
Back o he Old Days?
Ibai Ga cia-Taba *and Es eban M. Go os iaga
S udies, Resea ch and Spo s Medicine Cen e , Go e nmen o Na a e, Pamplona, Spain
Maximal Lac a e S eady S a e (MLSS) and Lac a e Th eshold (LT) a e
physiologically- ela ed and undamen al concep s wi hin he spo s and exe cise
sciences. Li e a u e suppo ing hei ela ionship, howe e , is sca ce. Among he
ecognized LTs, we we e pa icula ly in e es ed in he disused “Minimum Lac a e
Equi alen ” (LEmin), i s desc ibed in he ea ly 1980s. We hypo hesized ha eloci y
a LT, concep ually comp ehended as in he old days (LEmin), could p edic eloci y
a MLSS (VMLSS) mo e accu a e han some o he blood lac a e- ela ed h esholds
(BLRTs) ou inely used nowadays by many spo science p ac i ione s. Thi een male
endu ance- ained [VMLSS 15.0 ±1.1 km·h−1; maximal oxygen up ake ( ˙
VO2max) 67.6
±4.1 ml·kg−1·min−1] homogeneous (coe icien o a ia ion: ≈7%) unne s conduc ed
1) a submaximal discon inuous inc emen al unning es o de e mine se e al BLRTs
ollowed by a maximal amp inc emen al unning es o ˙
VO2max de e mina ion, and
2) se e al (4–5) cons an eloci y unning es s o de e mine VMLSS wi h a p ecision
o 0.20 km·h−1. De e mined BLRTs include LEmin and LEmin- ela ed LEmin plus 1
(LEmin+1 mM) and 1.5 mmol·L−1(LEmin+1.5 mM), along wi h well-es ablished BLRTs such
as con en ionally-calcula ed LT, Dmax and ixed blood lac a e concen a ion h esholds.
LEmin did no di e om LT (P=0.71; ES: 0.08) and was 27% lowe han MLSS
(P<0.001; ES: 3.54). LEmin+1 mM was no di e en om MLSS (P=0.47; ES: 0.09).
LEmin was he bes p edic o o VMLSS ( =0.91; P<0.001; SEE =0.47 km·h−1),
ollowed by LEmin+1 mM ( =0.86; P<0.001; SEE =0.58 km·h−1) and LEmin+1.5 mM
( =0.84; P<0.001; SEE =0.86 km·h−1). The e was no s a is ical di e ence be ween
MLSS and es ima ed MLSS using LEmin p edic ion o mula (P=0.99; ES: 0.001). Mean
bias and limi s o ag eemen we e 0.00 ±0.45 km·h−1and ±0.89 km·h−1. Addi ionally,
LEmin, LEmin+1 mM and LEmin+1.5 mM we e he bes p edic o s o ˙
VO2max ( =0.72–0.79;
P<0.001). These esul s suppo LEmin, an objec i e submaximal o e looked and
unde used BLRT, o be one o he bes single MLSS p edic o s in endu ance ained
unne s. Ou s udy ad oca es ac o s con olling LEmin o be sha ed, a leas pa ly, wi h
hose con olling MLSS.
Keywo ds: lac a e h eshold, ae obic capaci y, Owles’ poin , oxygen endu ance pe o mance limi , ae obic
h eshold, anae obic h eshold, endu ance assessmen , submaximal exe cise es ing
Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
INTRODUCTION
The exe cise in ensi y co esponding o he maximal lac a e
s eady s a e (MLSS) is a consis en physiological phenomenon
desc ibing he highes cons an eloci y o powe ou pu ha
can be main ained o e ime wi hou con inual blood lac a e
concen a ion (BLC) accumula ion (Beneke, 1995). Nowadays
MLSS is conside ed he gold s anda d endu ance pe o mance
ma ke among he as majo i y o spo and exe cise science
physiologis s (Beneke, 1995; Llodio e al., 2016; Messias e al.,
2017). MLSS is aluable, and mo e sensi i e han maximal
oxygen up ake ( ˙
VO2max), o diagnose endu ance pe o mance
(Coyle e al., 1988), guide ae obic aining (Ha e y e al., 1988),
e alua e endu ance aining-induced adap a ions (Philp e al.,
2008) and p edic endu ance pe o mance (Ha e y e al., 1988;
Jones and Dous , 1998). De e mina ion o MLSS is, howe e ,
cumbe some and in e e es wi h he a hle e’s aining p og am
since i equi es se e al (3–6) cons an wo kload es s on sepa a e
days leng hening ae obic condi ioning e alua ion o a minimum
o 1–3 week pe iod (Heck e al., 1985).
In an a emp o o e come he sho comings o mul iple-day
es ing, simple me hods ha e been p oposed o es ima e MLSS
om a single-day es , in ol ing he use o ei he BLC-based
measu emen s o some o he bloodless simple measu emen s
such as he peak wo kload eached du ing an inc emen al
maximal es . Nume ous s udies conduc ed on compe i i e
a hle es ha e shown ha he in ensi ies co esponding o some
blood lac a e- ela ed h esholds (BLRTs), such as he Onse
o Blood Lac a e Accumula ion (OBLA) (Beneke, 1995; Van
Schuylenbe gh e al., 2004), Indi idual Anae obic Th eshold
(IAT) (Beneke, 1995), Dmax (Van Schuylenbe gh e al., 2004)
o he Lac a e Minimum Tes (LMT) (Jones and Dous , 1998),
p edic MLSS wi h a wide ange o co ela ion magni udes
( =0.61–0.85). Howe e , hese co ela ion magni udes a e
equal, o e en lowe , han he ones epo ed in hose same s udies
when he peak wo kload a ained du ing an inc emen al maximal
es was used as MLSS p edic o ( =0.85–0.94).
Be o e he appea ance o he MLSS concep and based on
he ea ly wo ks o Ba and Himwich (1923) and Owles (1930)
published in he 1920s, se e al esea che s independen ly ound
ha du ing g aded inc emen al exe cise he e is a c i ical exe cise
in ensi y le el unique o each indi idual abo e which BLC
ini ia es o inc ease beyond es ing alues. In he ollowing
yea s his c i ical wo kload le el, which always occu s a lowe
in ensi ies han MLSS (Lehmann e al., 1983; Aunola and
Rusko, 1988; Faude e al., 2009; Fe guson e al., 2018) and is
equen ly called “Lac a e Th eshold (LT)” (Jones and Eh sam,
1982) [al hough i has also been e med “Owles’ Poin ” (Jones
and Eh sam, 1982), “Oxygen Endu ance Pe o mance Limi ”
(Hollmann, 1985), “Ae obic Th eshold” (Kinde mann e al., 1978)
o “Anae obic Th eshold” (Wasse man e al., 1973)], was widely
conside ed as he s anda d c i e ion measu e o de e mine
ae obic capaci y (Wel man e al., 1987; Mezzani e al., 2012),
p edic endu ance pe o mance (Yoshida e al., 1990), and design
endu ance exe cise aining p og ams (Wel man e al., 1990);
u ning LT in o a pi o al concep wi hin he spo s medicine
and exe cise sciences. No wi hs anding, he e a e s ill some
ele an me hodological limi a ions on he accu a e and igo ous
de e mina ion o LT, mainly when (a) i is de e mined by simple
isual inspec ion o BLC-da a plo ed agains wo kload due o
he subjec i i y o he analysis and poo in e - iewe and in e -
me hod ag eemen (Yeh e al., 1983), (b) he ini ial wo kload
and subsequen ini ial wo kload inc emen s a e no low enough
o allow a p elimina y BLC-baseline phase on he BLC kine ics
du ing he g aded exe cise (Hollmann, 1985), and (c) he BLC-
da a-poin in e al is oo la ge o de ec LT wi h a sui able
sensi i i y (Hollmann, 1985). Beyond a shadow o a doub ,
objec i e me hodological app oaches and app op ia e igo ous
p o ocols a e needed o o e come hese limi a ions (B ooks,
1985).
Despi e MLSS and LT being physiologically di e en , bu
p obably ela ed, undamen al concep s wi hin he spo s and
exe cise sciences (Fe guson e al., 2018), li e a u e conce ning
hei ela ionship is sca ce. As a as he au ho s a e awa e,
whe he he eloci y a LT (VLT) ob ained du ing an inc emen al
exe cise es p edic s he eloci y a MLSS (VMLSS) in endu ance
ained unne s has no been ully explo ed, and dese es
u he a en ion. We hypo hesized ha VLT, concep ually
comp ehended as in he old days (Owles, 1930), could p edic
VMLSS mo e accu a e han some o he s BLRTs used nowadays by
many au ho s and o he spo science p ac i ione s. Acco dingly,
he p ima y pu pose o his s udy was o de e mine he
applicabili y o he classical gold s anda d LT,calcula ed
objec i ely and in a s anda dized manne , o p edic VMLSS in
compa ison wi h some o he mo e commonly used pa ame e s
o BLC changes du ing inc emen al exe cise in a homogeneous
g oup o endu ance ained unne s. Among he ecognized
BLRTs (Faude e al., 2009) we we e pa icula ly in e es ed in
he “Minimum Lac a e Equi alen ” (LEmin), ini ially desc ibed
by Ge man au ho s in he ea ly 1980s (Be g e al., 1980;
Lehmann e al., 1983). LEmin is he minimum alue o he
BLC/wo kload s. wo kload cu e i ing du ing an inc emen al
exe cises es . Using an app op ia e p o ocol wi h adequa e
opening and inc emen al wo kloads, he inc emen al es
p oduces an idiosync a ic “U-shaped” cu e i ing p o ile
allowing ma hema ical impa ial loca ion o he ansi ion a
VLT wi h a e y ine esolu ion. This seldom used me hod
(LEmin) should no be con used wi h he much mo e popula
“Lac a e Minimum Tes ” (LMT), which was o iginally desc ibed
by Teg bu e al. (1993) and uses a p elimina y ela i ely
high le el o exe ion phase (hype lac a emia phase) o se -
up he men ioned “U-shaped” cu e i ing p o ile hampe ing
hea a e (HR) da a in e p e a ion, and he e o e, i s on- ield
applica ion.
A seconda y pu pose o his s udy was o de e mine he
ex en o which some a iables no equi ing blood sampling,
such as ˙
VO2max, peak eadmill eloci y (PTV) o he eloci y
co esponding o he 90% o maximal hea a e (V90) (Ga cia-
Taba e al., 2015b), a e o po en ial in e es o es ima e VMLSS.
To he bes o ou knowledge li e a u e conce ning VMLSS
p edic ion om such a iables in well- ained endu ance unne s
is limi ed. Assessmen and moni o ing o ae obic capaci y in
his kind o a hle es is o pa amoun impo ance (Halson, 2014),
and consequen ly, his s udy has he po en ial o con ibu e wi h
F on ie s in Physiology | www. on ie sin.o g 2July 2018 | Volume 9 | A icle 1034
Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
no ewo hy scien i ic-based p ac ical endu ance pe o mance
implica ions.
MATERIALS AND METHODS
Subjec s
Fi een male ained middle- and long-dis ance unne s we e
ec ui ed om egional a hle ic clubs. Runne s we e equi ed
o mee he ollowing inclusion c i e ia: (1) being male unne s
aged be ween 18 and 40; (2) ha ing a VMLSS >13 km·h−1,
and (3) a aining ou ine o ≥3 ae obic unning aining
sessions pe week. Exclusions c i e ia we e: (1) being aking
any medica ion/supplemen a ion ha could a ec BLC o HR
alues and (2) ha ing any known ca dio ascula , espi a o y o
ci cula o y dys unc ion. One unne wi hd ew om he s udy
due o pe sonal easons and ano he unne did no mee he
inclusion c i e ia. Thi een unne s comple ed he s udy. Mean
(±SD) age, heigh , body mass and pe cen age o body a o he
hi een pa icipan s we e 28 ±7 y, 1.76 ±0.05 m, 68.8 ±6.8 kg
and 8.8 ±3.1%, espec i ely. Runne s compe ed in aces anging
om 800-m o hal -ma a hon.
The s udy was conduc ed acco ding o he guidelines laid
down in he Decla a ion o Helsinki and all p ocedu es we e
app o ed by he local Ins i u ional Re iew Commi ee o he
Ins i u o Na a o del Depo e y Jue en ud (Go e nmen o
Na a e, Spain). Inclusion and exclusion c i e ia, expe imen al
a ionale, es ing p ocedu es and associa ed isks and bene i s
o pa icipa ion we e ully explained o pa icipan s and hei
coaches by an o al p esen a ion. P io o any es ing, pa icipan s
acknowledged olun a y pa icipa ion h ough w i en in o med
consen .
S udy Design
A p edic i e c oss-sec ional s udy was conduc ed o de e mine
VMLSS om a single-session submaximal discon inuous
inc emen al unning es (SD-IRT). Pa icipan s conduc ed
7–8 labo a o y es ing sessions. (1) Hea h sc eening session:
a maximal amp inc emen al cycling es o disca d any
ca dio ascula anomaly (12-lead elec oca diog am, GE
Heal hca e, CASE Ma que e, Ge many). (2) Familia iza ion
session: a SD-IRT o accus om o he es ing eadmill unning
p o ocol. This session was also u ilized o an h opome ic
e alua ion. (3) BLRTs and ˙
VO2max es ing session: he SD-IRT
p e iously used in he amilia iza ion session o de e mine
BLRTs, ollowed by a maximal amp inc emen al unning es
(MR-IRT) o de e mine ˙
VO2max. (4) VMLSS es ing: 4–5 cons an
eloci y unning es s (CVRTs) o VMLSS de e mina ion.
Tes ing P ocedu es
Pa icipan s we e equi ed o comple e he s udy wi hin 6 weeks.
Tes ing sessions we e pe o med a he same ime o he day o
lessen ci cadian a iabili y, we e p eceded by 2 days o es o
e y ligh exe cise [<90 min a <70% maximal HR (HRmax)]
and we e sepa a ed om he las compe i i e ace by ≥4 days
o allow es o a ion o muscle glycogen. Runne s a i ed o
each es ing session in a es ed and ully hyd a ed s a e, 2 h
pos p andial, ha ing abs ained om ca eina ed and alcoholic
be e ages du ing he day. Subjec s we e asked o eplica e
die and exe cise egimens he 2 days p eceding each es ing
session o limi luc ua ions o ini ial glycogen concen a ion
be ween ials (Van Schuylenbe gh e al., 2004; Philp e al.,
2008). Pa icipan s eco ded hei exe cise aining and die
h oughou he expe imen al phase o he s udy on aining
and die logs designed and p o ided by he au ho s. These
de ailed exe cise and die logs se ed o con i m ul illmen o
die and exe cise ins uc ions gi en o he 2 days p eceding
each es ing session, and e i ied ha only mino changes in
aining and ae obic condi ioning occu ed du ing he s udy
(Fa ell e al., 1979). Pa icipan s wo e he same unning aine s
on each expe imen al day. Tes ing ook place du ing May-June,
i.e., beginning o he ou doo compe i i e season. All p ocedu es
we e conduc ed on he same unning e gome e (Kun a äline,
Hype T eadmill 2040, Finland) wi h he g adien se a 1%,
unde empe a u e (22.3 ±1.4◦C), humidi y (33 ±4%) and
luminosi y con olled labo a o y condi ions.
BLRTs and ˙
VO2max Tes ing
A hle es pe o med a SD-IRT o BLRTs de e mina ion, ollowed
by a MR-IRT o de e mine hei ˙
VO2max. The submaximal
ial began a 7 km·h−1. Speed was inc eased by 1 km·h−1
e e y 2-min, wi h 1-min in e als be ween s ages un il a BLC
≥3 mmol·L−1was obse ed. On he basis ha 1- o 4-min
s age du a ion p o ocols do no no ably a ec BLRTs de ec ion
(Yoshida, 1984), 2-min du a ion s ages we e chosen no o
unnecessa y leng hen he SD-IRT acco ding o p e ious LEmin
de ec ion p o ocols (Be g e al., 1980, 1990; Lehmann e al.,
1983; Aunola and Rusko, 1988). Immedia ely a e each s age,
capilla y blood samples o BLC measu emen s we e ob ained.
A e a 10-min es , subjec s began he MR-IRT. Ini ial speed
was 10 km·h−1and was inc eased by 1 km·h−1e e y min un il
oli ional exhaus ion. Volun ee s we e igo ously encou aged
o comple e exhaus ion. Pos -exe cise capilla y blood samples
a e 3 min o passi e eco e y we e ob ained o peak BLC
(BLCpeak) de e mina ion. HR du ing bo h ials (Pola Elec o
Oy, RS800CX, Finland) and me abolic da a du ing he MR-
IRT (Vis a Mini-CPX, Vacu-Med, Sil e Edi ion 17670, Ven u a,
CA, USA) we e moni o ed and a e aged o e 30-s. PTV,
HRmax (Ga cia-Taba e al., 2017) and ˙
VO2max (Ga cia-Taba
e al., 2015a) we e de e mined ollowing p ocedu es p e iously
desc ibed.
VMLSS Tes ing
On subsequen labo a o y isi s, unne s comple ed 4–5 CVRTs.
Each CVRT consis ed o 30-min unning a he selec ed speeds
wi h 1-min in e up ions e e y 10-min o blood sampling (i.e.,
32-min du a ion CVRTs). Capilla y blood samples we e ob ained
a es , and a min 10, 21 and 32 o exe cise. An inc ease in BLC
<1.0 mmol·L−1du ing he las 20 min o exe cise (i.e., be ween
he 10 h and he 32nd min o he CVRT) was de ined as he
c i e ion o BLC o be conside ed a a s eady s a e (Beneke,
1995). VMLSS was de ined as he highes unning eloci y
mee ing his s abili y c i e ion. Running eloci y o he i s
CVRT co esponded o app oxima ely 80% o he PTV achie ed
du ing he maximal ial. Depending on he BLC s abili y o
F on ie s in Physiology | www. on ie sin.o g 3July 2018 | Volume 9 | A icle 1034
Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
his i s CVRT, he eloci y was inc eased o dec eased in he
ollowing CVRTs. I du ing he i s CVRT a s eady s a e o
dec ease in BLC was ound, he eloci y o he nex CVRT
was inc eased by 0.4 km·h−1. Con e sely, i an inc ease in BLC
supe io o he s abili y c i e ion was obse ed, unning eloci y
o he nex CVRT was dec eased by 0.4 km·h−1. This p ocess
o inc easing o dec easing unning eloci y by 0.4 km·h−1, and
la e by 0.2 km·h−1, was u he epea ed in subsequen es s un il
VMLSS was de e mined wi h a p ecision o 0.2 km·h−1. HR was
moni o ed and a e aged as abo emen ioned.
Blood Sampling and Blood Lac a e
Concen a ion (BLC) De e mina ion
A hype emic ea lobe was cleaned and d ied be o e punc u ing
by a lance de ice o aspi a e a 5 µL whole blood sample in o
an enzyme-coa ed elec ode es s ip. BLC was de e mined ia
ampe ome ic measu emen using a po able analyze (A k ay
KDK Co po a ion, Lac a e P o LT-1710, Shiga, Japan) calib a ed
be o e e e y es . Manu ac u e s epo coe icien s o a ia ion
(CVs) o 3.2 and 2.6% o lac a e s anda ds o 2 and 11 mmol·L−1,
espec i ely.
De e mina ion o Blood Lac a e-Rela ed
Th esholds (BLRTs)
Nine di e en BLRTs we e de e mined. LT0.2 mM and LT1.
LT0.2 mM was de ined as he s age p io o a ≥0.2 mmol·L−1
BLC ele a ion abo e baseline alues (S a on e al., 2009).
To o e come he e o associa ed wi h he analyze (Wel man
e al., 1987), he highes s age abo e which BLC inc eased by
≥0.1 mmol·L−1in he ollowing s age and ≥0.2 mmol·L−1
in he subsequen s age was also chosen as a h eshold and
named LT1. LEmin, LEmin+1 mM and LEmin+1.5 mM. The eloci y
co esponding o he Minimum Lac a e Equi alen (VLEmin)
(Be g e al., 1990) was conside ed he minimum alue o
he quo ien BLC/ eloci y in he indi idual BLC/ eloci y s.
eloci y second-o de polynomial cu es. Veloci y associa ed
wi h he Minimum Lac a e Equi alen plus 1 (VLEmin+1 mM)
and 1.5 mmol·L−1(VLEmin+1.5 mM) we e de ined as he
unning eloci ies a 1.0 and 1.5 mmol·L−1abo e VLEmin
in he indi idual BLC s. eloci y second-o de polynomial
cu es, espec i ely. Dmax. Veloci y a Dmax was conside ed
he maximum pe pendicula dis ance om he s aigh line
be ween he i s and inal BLC da a-poin s o he hi d-o de
polynomial cu e desc ibing he BLC kine ics du ing he SD-IRT
(Cheng e al., 1992). Fixed blood lac a e concen a ion (FBLC)
h esholds. Veloci ies a FBLC h esholds o 2 (FBLC2 mM), 2.5
(FBLC2.5 mM) and 3 mmol·L−1(FBLC3 mM) commonly use in eal
p ac ice (Seile , 2010; Ga cia-Taba e al., 2017) we e de e mined
om he indi idual BLC s. eloci y second-o de polynomial
cu es. De e mina ion o BLRTs is illus a ed in Figu e 1.
Veloci ies a he BLRTs we e de e mined using MATLAB
R2015a (The Ma hWo ks Inc., Na ick, MA, USA). Coe icien s
o de e mina ion (R2) o he indi idual second- and hi d-o de
BLC s. eloci y and second-o de BLC/ eloci y quo ien s.
eloci y polynomial cu es we e all >0.90. Veloci ies a BLRTs
(Wel man e al., 1990), as well as VMLSS (Hause e al., 2013),
equen ly show es - e es in aclass co ela ion coe icien s
>0.94, and CVs ≤3%. HR alues a he BLRTs we e compu ed
om he indi idual HR s. eloci y linea eg ession equa ions
( >0.98; P<0.001). V90 was also calcula ed om he indi idual
linea HR s. eloci y eg essions ob ained du ing he SD-IRTs
(Ga cia-Taba e al., 2017).
S a is ics
S anda d s a is ical me hods we e used o he calcula ion
o means, s anda d de ia ions (SD), s anda d e o s o he
es ima es (SEE) and con idence in e als (CI). Da a we e
analyzed using pa ame ic s a is ics ollowing con i ma ion
o no mali y (Kolmogo o –Smi no es ), homoscedas ici y
(Le ene’s es ), and when app op ia e sphe ici y (Mauchly’s
es ). The G eenhouse-Geisse co ec ion ac o o educe he
isk o ype I e o was applied whe e sphe ici y assump ions
we e iola ed. S uden ’s pai ed - es s we e used o e alua e
di e ences be ween each BLRT wi h MLSS. The magni udes o
he di e ences we e assessed using 90% CI and Hedges’ ge ec
sizes (ES) (Hedges, 1981). Di e ences we e conside ed non-
subs an ial i he 90% CIs o e lapped ze o. ES alues o 0.2,
0.5, and >0.8 we e conside ed o ep esen small, mode a e,
and la ge di e ences, espec i ely. Di e ences in BLC and HR
along he CVRTs we e iden i ied by one-way epea ed measu es
ANOVA wi h Bon e oni co ec ion o mul iple compa isons.
Two- ac o ial ANOVA wi h he Sche é pos -hoc es was used
o iden i y di e ences in BLC and HR be ween he CVRTs
a VMLSS and a 0.2 km·h−1abo e VMLSS (VMLSS+0.2).
Linea eg ession analyses wi h Pea son’s co ela ion coe icien s
( ) we e pe o med o de e mine he ela ionships be ween
he a iables o in e es . When pe inen , slopes o eg ession
lines we e compa ed using analysis o co a iance (ANCOVA).
Ag eemen wi h he e e ence me hod (VMLSS) was assessed
by mean bias and limi s o ag eemen (LOAs) (K ouwe , 2008).
Pos -hoc powe calcula ion o he linea eg essions, assuming
ype I e o o 0.05, indica ed a powe >99%. Analyses we e
pe o med using IMB SPSS S a is ics 22 (IBM Co po a ion, NY,
USA). Signi icance was se a P<0.05 o he analyses ha did no
equi e pos -hoc adjus men . Desc ip i e s a is ics a e epo ed as
means (±SD).
RESULTS
BLRTs and ˙
VO2max Tes ing
The SD-IRT las ed 32:00 ±4:24 min:s. Runne s achie ed a
eadmill eloci y o 17.0 ±1.5 km·h−1( ange 15.0–19.0).
BLC and %HRmax a comple ion o he SD-IRT we e 3.4
±0.6 mmol·L−1( ange 3.0–5.4) and 92 ±2% ( ange 87–
93), espec i ely. Figu e 2 depic s BLC and %HRmax pa e n
esponses o he SD-IRT. Desc ip i e cha ac e is ics o he BLRTs
a e depic ed in Table 1. BLC es ing alues p io o he beginning
o he MR-IRT we e 1.1 ±0.2 mmol·L−1( ange 0.8–1.7). Table 2
elucida ed he maximal na u e o he MR-IRT.
VMLSS Tes ing
Desc ip i e ea u es o he MLSS a e displayed along wi h he
BLRTs (Table 1). Veloci y a LEmin did no di e om ha a
F on ie s in Physiology | www. on ie sin.o g 4July 2018 | Volume 9 | A icle 1034
Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
FIGURE 1 | Illus a ion o blood lac a e- ela ed h esholds (BLRTs) de e mina ion in a ep esen a i e pa icipan . Dashed lines: second-o de polynomial cu e i s.
Do ed lines: he g ea es pe pendicula dis ance om he hi d-o de polynomial BLC- eloci y cu e i o he gene a ed s aigh line by he wo end da a-poin s o his
cu e. No e ha o clea ness o igu e p esen a ion, Dmax de e mina ion is illus a ed oge he wi h he es o BLRTs on a second-o de polynomial cu e i , al hough
ac ually i was de e mined on hi d-o de cu ilinea i s as o iginally desc ibed (Cheng e al., 1992).
LT1(P=0.71; 90% CI: −0.74 o 0.47; ES: 0.08) and was 27%
lowe han VMLSS (P<0.001; 90% CI: −3.80 o −2.83; ES: 3.54).
Veloci ies a FBLC2 mM (P=0.50; 90% CI: −0.69 o 0.30; ES:
0.15) and LEmin+1 mM (P=0.47; 90% CI: −0.17 o 0.42; ES: 0.09)
we e no di e en om VMLSS. V90 (16.1 ±1.2 km·h−1, ange
13.9–18.1) was 1.1 km·h−1(7%) highe han VMLSS (P<0.001;
90% CI: 0.77–1.53; ES: 0.96), and no di e en om eloci y a
FBLC2.5 mM (P=0.619; 90% CI: −0.27 o 0.49; ES: 0.09) and
VLEmin+1.5 mM (P=0.543; 90% CI: −0.42 o 0.87; ES: 0.15). HR
associa ed wi h VMLSS du ing he SD-IRT was 86 ±5% HRmax,
and was no di e en om %HRmax a FBLC2 mM (P=0.93;
90% CI: −2.99 o 3.29; ES: 0.01), LEmin+1 mM (P=0.92; 90%
CI: −2.56 o 2.86; ES: 0.04) and FBLC2.5 mM (P=0.08; 90%
CI: 0.25–6.55; ES: 0.78). BLC and %HRmax esponses o he
CVRTs pe o med a VMLSS and a VMLSS+0.2 a e illus a ed
in Figu e 3. One unne exhaus ed a min 29 o he CVRT a
F on ie s in Physiology | www. on ie sin.o g 5July 2018 | Volume 9 | A icle 1034
Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
FIGURE 2 | Mean (SD) blood lac a e and hea a e esponses o he submaximal discon inuous inc emen al unning exe cise es . All subjec s e mina ed he
15 km·h−1exe cise s age. Mean (SD) alues a comple ion o he es o subjec s achie ing ≥16 km·h−1a e indica ed by dashed lines.
TABLE 1 | Desc ip i e ea u es o he de e mined blood lac a e- ela ed h esholds and maximal lac a e s eady s a e (MLSS) (n=13).
km·h−1%MLSSV%PTV %HRmax
Mean ±SD Range Mean ±SD Range Mean ±SD Range Mean ±SD Range
LEmin 11.6 ±0.8** 10.5–12.6 77 ±2** 74–80 58 ±3** 55–64 75 ±5** 63–80
LT111.7 ±1.7** 9.0–14.0 78 ±7** 64–88 59 ±7** 47–70 76 ±4** 66–83
LT0.2 mM 12.5 ±1.4** 10.0–15.0 84 ±6** 73–94 63 ±5** 52–70 79 ±3** 70–83
Dmax 13.2 ±1.2** 11.5–14.6 87 ±4** 81–95 66 ±4** 59–73 81 ±2** 77–85
FBLC2 mM 14.8 ±1.5 12.8–17.0 99 ±7 84–107 75 ±5 67–82 86 ±3* 80–90
MLSS 15.0 ±1.1 13.3–16.5 100 ±N/A N/A 76 ±4 69–82 91 ±4 83–95
LEmin+1 mM 15.1 ±1.2 13.7–16.8 101 ±4 95–106 76 ±4 70–85 86 ±3* 80–90
FBLC2.5 mM 15.9 ±1.5* 14.0–18.1 106 ±6* 94–114 80 ±5* 73–88 90 ±3 84–94
LEmin+1.5 mM 15.9 ±1.4* 13.0–18.1 106 ±6* 94–113 81 ±5* 70–89 90 ±3 86–93
FBLC3 mM 16.8 ±1.5** 15.0–19.1 112 ±6** 102–120 85 ±5** 78–93 92 ±3 87–97
LEmin, minimum lac a e equi alen ; LT1, he highes s age abo e which blood lac a e concen a ion inc eased by ≥0.1 mmol·L−1in he ollowing s age and ≥0.2 mmol·L−1in he
subsequen s age; LT0.2 mM, he s age p io o a ≥0.2 mmol·L−1blood lac a e concen a ion ele a ion abo e baseline alues; Dmax , Maximal-De ia ion me hod; FBLC2mM, ixed blood
lac a e concen a ion (FBLC) h eshold o 2 mmol·L−1; LEmin+1mM, LEmin plus 1 mmol·L−1; FBLC2.5 mM, FBLC h eshold o 2.5 mmol·L−1; LEmin+1.5 mM, LEmin plus 1.5 mmol·L−1;
FBLC3mM, FBLC h eshold o 3 mmol·L−1.
*Signi ican ly di e en om MLSS (P <0.01).
**Signi ican ly di e en om MLSS (P <0.001).
VMLSS+0.2, and did no e mina e he ial. BLC du ing he
CVRT a VMLSS+0.2 inc eased >1 mmol·L−1 om he min 10
o he end o he ial (1.6 ±0.7 mmol·L−1;P<0.001; 90%
CI: 1.26–1.95; ES: 0.82). Du ing he CVRT a VMLSS, BLC om
he 10 h min o he end o he exe cise inc eased signi ican ly
(0.4 ±0.4 mmol·L−1;P=0.02; 90% CI: 0.20–0.63; ES: 0.31),
bu he inc emen was <1 mmol·L−1in e e y single case. This
BLC s abili y c i e ion was ob ained a ≈3.9 ±1.3 mmol·L−1
( ange ≈2.1–6.2). HR inc eased (P<0.01) o e he cou se o
bo h VMLSS and VMLSS+0.2 CVRTs. Du ing he VMLSS CVRT,
absolu e HR inc eased 7 ±4 b·min−1(P<0.001; 90% CI: 5.0–
9.0; ES: 0.70) om min 10 o he end o he es . HR (%HRmax) a
min 5, 10, 21 and 32 o he VMLSS CVRT we e 85 ±3, 88 ±3, 91
±4 and 92 ±4%, espec i ely.
Co ela ions and Ag eemen Be ween he
Measu ed Pe o mance Va iables
E e y bloody and bloodless measu ed endu ance pe o mance
a iables co ela ed signi ican ly wi h VMLSS (Table 3). VLEmin
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Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
TABLE 2 | Maximal alues a ained du ing he maximal amp inc emen al unning
es (n=13).
Mean ±SD Range
Tes du a ion (min:s) 12 :36 ±00 :54 11:18–14:12
PTV (km·h−1) 19.8 ±0.9 18.6–21.4
˙
VOmax(ml·kg−1·min−1) 67.6 ±4.1 61.8–73.7
˙
VEmax (L·min−1) 128 ±12 104–144
HRmax (b·min−1) 184 ±9 167–199
HRmax (% age p edic ed HRmax) 95 ±5 88–101
RERmax 1.18 ±0.05 1.09–1.26
BLCpeak (mmol·L−1) 7.6 ±2.0 5.6–11.8
PTV, peak eadmill eloci y; ˙
VOmax , maximal oxygen up ake; ˙
VEmax , maximal minu e
en ila ion; HRmax, maximal hea a e; RERmax , maximal espi a o y exchange a io;
BLCpeak, peak blood lac a e concen a ion.
was he bes p edic o o VMLSS (Figu e 4), ollowed by
VLEmin+1 mM ( =0.86; P<0.001; SEE =0.58; 95% CI: 0.50–
1.13) and VLEmin+1.5 mM ( =0.84; P<0.001; SEE =0.86;
95% CI: 0.58–1.57). The e was no s a is ical di e ence be ween
VMLSS and es ima ed VMLSS using he o mula exposed in
Figu e 4 (P=0.99; 90% CI: −0.22 o 0.22; ES: 0.001). Mean
bias and LOAs we e 0.00 ±0.45 km·h−1and ±0.89 km·h−1,
espec i ely, indica ing ha p edic ion o VMLSS om VLEmin
could be biased up o 5.9% abo e o below ac ual VMLSS.
VLEmin+1 mM did no di e om VMLSS (P=0.47; 90% CI:
−0.17 o 0.42; ES: 0.09). Mean di e ence was −0.12 ±0.6 km·h−1
and LOAs we e ±1.18 km·h−1(±7.8%).
Ve y la ge associa ions be ween VLEmin and VMLSS in
absolu e alues (km·h−1) wi h hei espec i e eloci ies in
ela i e alues (%PTV) we e obse ed (Figu e 5). Acco ding o
he ANCOVA esul s, he slopes o hese bo h eg ession lines
we e no di e en (P>0.05). Ve y la ge associa ions we e also
ound be ween HR a LEmin (HRLEmin) and HR h oughou he
VMLSS CVRT. These co ela ion magni udes we e =0.90
(Figu e 6), =0.85 (P<0.001; SEE =4.9; 95% CI: 0.30–0.83),
=0.79 (P=0.004; SEE =6.6; 95% CI: 0.25–0.96) and =0.74
(P=0.009; SEE =7.9; 95% CI: 0.20–1.06) o HR a min 5, 10, 21,
and 32 o he VMLSS CVRT, espec i ely. Due o some echnical
p oblems wi h he HR moni o s, HR linea eg essions a e based
upon 11 da a-poin s.
DISCUSSION
The majo inding o his s udy was ha VLEmin was he s onges
p edic o o VMLSS, ollowed by VLEmin+1 mM,VLEmin+1.5 mM,
LT1and he es o he p edic o a iables (Table 3). These
indings a e in line wi h p e ious esea ch showing ha BLRTs,
such as OBLA (Beneke, 1995; Van Schuylenbe gh e al., 2004;
Denadai e al., 2005; Vobejda e al., 2006; Figuei a e al.,
2008; G ossl e al., 2012), IAT (Beneke, 1995), Dmax (Van
Schuylenbe gh e al., 2004), LT (Philp e al., 2008), o o he
BLRTs (G ossl e al., 2012) ob ained du ing an inc emen al single-
es a e signi ican de e minan s o MLSS. The high sus ained
a iance by VLEmin in VMLSS p edic ion in his s udy (83%,
Figu e 4) is among he highes epo ed in he li e a u e (50–
88%). Homogenei y o he sample, speci ici y and cha ac e is ics
o he es p o ocol, p ecision and s abili y c i e ion in MLSS
de e mina ion, as well as he exac a iables de i ed om
he inc emen al es chosen o BLRTs de e mina ion a e
po en ial ac o s a ec ing co ela ion magni ude di e ences
among s udies. Fo ins ance, endu ance ained unne s in he
p esen s udy we e ela i ely homogeneous in e ms o VMLSS
(CV ≈7%), and de e mina ion o hei MLSS was e y accu a e
(±0.2 km·h−1;±1.3% mean VMLSS). In con as , s udy samples
in he abo e-ci ed publica ions we e mo e he e ogeneous (CVs
7–16%) and p ecision in MLSS de e mina ion was much lowe
(7–15%), which a e ac o s ha can bias compa isons be ween
s udies. Conce ning he a o emen ioned s udies ca ied ou
in unne s, LT (Philp e al., 2008) and OBLA (Vobejda
e al., 2006) highly co ela ed wi h VMLSS, accoun ing o 72
and 81% o he a iance, espec i ely. Howe e , accu acy in
VMLSS de e mina ion (3–4% mean VMLSS) was lowe han
in ou s udy and he s udy samples composed o male and
emale unne s we e he e ogeneous (VMLSS CVs 12–16%). I
is well es ablished ha he e ogenei y o he samples causes
o e es ima ion o co ela ion magni udes; he g ea e he ange
o he he e ogenei y o a g oup, he g ea e he magni ude o he
co ela ion coe icien .
Wi h ega d o p edic ion accu acy, i is wo h men ioning he
ela i ely low SEE (0.47 km·h−1; 3.1% mean VMLSS) in VMLSS
p edic ion om VLEmin ound in his s udy (Figu e 4). This SEE
is lowe han he accu acy in MLSS iden i ica ion commonly
u ilized (as discussed in he p e ious pa ag aph) and compa es
a o ably wi h o he s udies p edic ing MLSS om he in ensi y
associa ed wi h OBLA, whe e SEE alues o ≈5.5% (Vobejda
e al., 2006; Figuei a e al., 2008) and 20.7% (Figuei a e al., 2008)
o mean MLSS we e epo ed o unning and cycling exe cise
modes, espec i ely. The Bland-Al man’s LOAs (±0.89 km·h−1;
i.e., ±5.9% mean VMLSS) a e also na owe compa ed o hose o
o he s udies p edic ing MLSS om LMT (±6.6% mean MLSS)
(So e o e al., 2009), OBLA (±10.3%) (G ossl e al., 2012) o
o he BLRTs (±9.5–16.5%) (G ossl e al., 2012). The s eng h o
he ela ionship and p edic ion accu acy epo ed in he cu en
s udy suppo LEmin o p o ide a be e MLSS es ima ion han
o he BLRTs. This sugges s VLEmin, an objec i e submaximal
a iable calcula ed du ing a SD-IRT, o be one o he bes single
VMLSS p edic o in endu ance ained unne s.
The Minimum Lac a e Equi alen (LEmin) concep was
i s desc ibed in he 1980s by Ge man au ho s (Be g e al.,
1980, 1990; Lehmann e al., 1983) and was sugges ed o
objec i ely ep esen one o he wo men ioned gold s anda d
BLC h esholds, he exe cise in ensi y le el associa ed wi h he
beginning o BLC accumula ion abo e es ing alues du ing
g aded exe cise, nowadays known as Lac a e Th eshold (LT).
LEmin was de ined as he wo kload co esponding o he nadi
on he quad a ic ela ionship be ween BLC/wo kload (o ˙
VO2)
a io s. wo kload (o ˙
VO2) plo -da a de i ed om an SD-IRT.
Plo ing BLC/wo kload s. wo kload u ns he BLC-shape du ing
inc emen al exe cise in o a clea “U”-BLC-shape allowing he
obse a ion o BLC/wo kload dec emen o a nadi (LEmin) jus
be o e a clea BLC/wo kload inc emen (Figu e 1). In he p esen
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Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
FIGURE 3 | Mean (SD) blood lac a e ( iangles) and hea a e (ci cles) esponses o he cons an unning eloci ies es s (CVRTs) a he maximal lac a e s eady s a e
eloci y (open symbols) and a 0.2 km·h−1 as e eloci y ( illed symbols). * Signi ican ly di e en om he es o he ime-poin s wi hin he same CVRT (P<0.0125).
#Signi ican ly highe in compa ison wi h he co esponding ime-poin s a he maximal lac a e s eady s a e eloci y CVRT (P<0.0125).
s udy a e age VLEmin (11.6 km·h−1) app oxima e a e age VLT1
(11.7 km·h−1) (Table 1). This sugges s LEmin o ep esen he
pi o al equilib ium poin be ween blood lac a e p oduc ion and
emo al (Lehmann e al., 1983; Aunola and Rusko, 1988; Be g
e al., 1990). LEmin migh be associa ed wi h se e al physiological
cha ac e is ics and mechanisms, such as glycoly ic accele a ion,
muscle oxida i e capaci y, ype II muscle ibe ec ui men ,
in amuscula lac a e p oduc ion, lac a e elease and clea ance,
capilla y densi y and inc easing concen a ions o ci cula ing
ho mones (I y e al., 1980; Lehmann e al., 1983; Gladden,
2004). The eason why LEmin would o e signi ican p edic ion
ad an ages o e o he BLRTs o es ima e VMLSS can be ela ed
o: (1) he esolu ion o LEmin de e mina ion is ine han o he
BLRTs (e.g., LT) because all he da a poin s be o e and a e he
ansi ion a e used o p ojec he LEmin alue; (2) undesi ed e o
e ec s due o s a is ical sca e o he da a poin s a e minimized
by he leas squa es cu e- i ing p ocedu e; (3) LEmin could
essen ially ake on an in ini e numbe o alues, whe eas LT1
and LT0.2 mM could only be based on he disc e e alues o he
speci ic eloci y- a e s ages; (4) he oublesome iden i ica ion
o he i s BLC ele a ion abo e baseline alues (LT) due o
ini ial BLC luc ua ions associa ed wi h he e o o he analyze
(Wel man e al., 1987) is esol ed by he “U”-BLC-shape o LEmin
iden i ica ion wi hou he need o a p e ious high le el o exe ion
phase o induce hype lac a emia, as i is equi ed o LTM
iden i ica ion; and (5) ela i e changes in BLC based on he shape
and slope o he BLC/wo kload s. wo kload cu e (i.e., LEmin)
du ing inc emen al exe cise may be mo e ad an ageous, sensi i e
and obus compa ed wi h he use o absolu e BLC alues (i.e.,
FBLC h esholds) (Dickhu h e al., 1999). The ele ance o LEmin
as a p edic o a iable is unde pinned by he ac ha he o he
wo LEmin- ela ed h esholds (LEmin+1 mM and LEmin+1.5 mM)
we e he second and hi d a iables bes co ela ed wi h VMLSS.
Addi ionally, LEmin, LEmin+1 mM and LEmin+1.5 mM we e he bes
˙
VO2max p edic o s, whe eas a e age VLEmin+1 mM (15.1 km·h−1)
was nea ly iden ical o a e age VMLSS (15.0 km·h−1). This
sugges s ha VLEmin+1 mM may p o ide a close app oxima ion
o VMLSS.These esul s, he e o e, suppo LE/ unning- eloci y
o be a e y good p edic o o he indi idual and g oup a e age
VMLSS in endu ance ained unne s.
A subs an ial ela ionship ( =0.85) was obse ed be ween
VMLSS and %PTV a VMLSS. A simila co ela ion magni ude
( =0.83) was obse ed be ween VLEmin and %PTV a VLEmin.
Acco ding o ou p e ious obse a ions (Ga cia-Taba e al.,
2015b; Llodio e al., 2015, 2016) and o he s (Hu ley e al., 1984),
hese associa ions deno e ha hose unne s wi h highe VLEmin
and VMLSS a e mo e likely o possess hei VLEmin and VMLSS
a a highe %PTV (o % ˙
VO2max) compa ed o hose unne s
wi h lowe ae obic condi ioning. I also indica es ha %PTV and
%˙
VO2max do no adequa ely di e en ia e ac oss subjec s, and
subsequen ly, ha he ela i e PTV/ ˙
VO2max concep o aining
p esc ip ion pu poses should be used wi h cau ious (Ga cia-
Taba e al., 2017). P esc ibed aining by ela i e PTV/ ˙
VO2max
induces di e en aining adap a ion esponses (Buchhei e al.,
2010), mos p obably due o he di e ed le el o me abolic
acidosis ac oss indi iduals a a gi en %PTV o % ˙
VO2max (Ka ch
e al., 1978; Meye e al., 1999), as Figu e 5 depic s. One
in e es ing addi ional inding was ha VLEmin o VMLSS a io
was ema kably homogeneous among subjec s (77% VMLSS,
ange: 74–80%) in compa ison wi h he es o he BLRTs exposed
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Ga cia-Taba and Go os iaga Lac a e Equi alen (LE) s. MLSS
TABLE 3 | Pea son’s co ela ion magni udes be ween he selec ed endu ance pe o mance a iables (n=13).
LEmin LEmin + 1 mM LEmin + 1.5 mM LT1Dmax FBLC3 mM V90 FBLC2.5 mM PTV FBLC2 mM LT0.2 mM ˙
VO2max MLSS
LEmin 0.947*** 0.928*** 0.750** 0.756** 0.813*** 0.746** 0.778** 0.718** 0.692** 0.674** 0.724** 0.912***
LEmin+1 mM 0.900*** 0.684** 0.719** 0.817*** 0.783** 0.768** 0.674* 0.665* 0.713** 0.720** 0.863***
LEmin+1.5 mM 0.703** 0.779** 0.836*** 0.596* 0.793*** 0.771** 0.706** 0.641* 0.790*** 0.839***
LT10.821*** 0.910*** 0.860*** 0.924*** 0.770** 0.920*** 0.744** 0.528 0.836***
Dmax 0.895*** 0.891*** 0.909*** 0.743** 0.902*** 0.750** 0.374 0.827***
FBLC3 mM 0.850*** 0.995*** 0.793*** 0.967*** 0.773** 0.582* 0.804***
V90 0.872*** 0.669* 0.889*** 0.864*** 0.360 0.799**
FBLC2.5 mM 0.793*** 0.987*** 0.773** 0.526 0.792***
PTV 0.770** 0.777** 0.703** 0.760**
FBLC2 mM 0.745** 0.422 0.734**
LT0.2 mM 0.544 0.716**
˙
VO2max 0.597*
LEmin, minimum lac a e equi alen ; LEmin+1mM, LEmin plus 1 mmol·L−1; LEmin+1.5 mM, LEmin plus 1.5 mmol·L−1; LT1, he highes s age abo e which blood lac a e concen a ion inc eased by ≥0.1 mmol·L−1in he ollowing s age and
≥0.2 mmol·L−1in he subsequen s age; Dmax, Maximal-De ia ion me hod; FBLC3mM, ixed blood lac a e concen a ion (FBLC) h eshold o 3 mmol·L−1; V90, eloci y co esponding o 90% o maximal hea a e; FBLC2.5 mM, FBLC
h eshold o 2.5 mmol·L−1; PTV, peak eadmill eloci y; FBLC2mM, FBLC h eshold o 2 mmol·L−1; LT0.2 mM, he s age p io o a ≥0.2 mmol·L−1blood lac a e concen a ion ele a ion abo e baseline alues; ˙
VOmax , maximal oxygen
up ake.
*P<0.05, **P<0.01, ***P<0.001.
in Table 1 (e.g., 64–88% and 73–94% o LT1and LT0.2 mM,
espec i ely). This low ange (±3%) o he pe cen age o VMLSS
a which LEmin occu s is e y close o he limi o he es - e es
a iabili y o MLSS wo kload de e mina ion (Hause e al., 2013).
This indica es ha he VLEmin o VMLSS a io is independen o
he endu ance capaci y le el o he assessed unne s. Al hough
VMLSS is subs an ially highe han VLEmin, i is likely ha some
deg ee o commonali y exis s among hese wo physiological
pa ame e s sugges ing VLEmin as a majo VMLSS de e minan .
Ou s udy ad oca es ac o s con olling VLEmin o be sha ed, a
leas pa ly, wi h hose con olling VMLSS.
Conce ning ou seconda y pu pose, V90 was he bes
bloodless p edic o o VMLSS, accoun ing o 64% o he
a iance, ollowed by PTV (58%) and ˙
VO2max (36%) (Table 3).
The magni ude o he ela ionship be ween V90 and VMLSS was
simila o ha be ween FBLC h esholds and VMLSS. In addi ion,
V90 was a s ong ( =0.85–0.89) p edic o o FBLC h esholds.
These indings a e in close ag eemen wi h p e ious HR-based
s udies in p o essional eam-spo playe s (Ga cia-Taba e al.,
2015b), eli e Basque-ball playe s (Ga cia-Taba e al., 2017) and
low-le el (VMLSS ≈13.6 km·h−1) endu ance unne s (Kuphal
e al., 2004) in which V90 was la gely associa ed wi h VMLSS
(Kuphal e al., 2004) and FBLC h esholds (Ga cia-Taba e al.,
2015b, 2017). The ele ance o V90 as a bloodless p edic o
o BLRTs is s eng hened by (1) he ela ionship be ween V90
and BLRTs is qui e s able despi e al e a ions in BLRTs due o
aining, de aining o hypoxia (Hu ley e al., 1984; Fos e e al.,
1999; F iedmann e al., 2004); (2) inc eases in V90 ha e been
e i ied o p edic longi udinal aining-induced imp o emen s
in FBLC h esholds (Ga cia-Taba e al., 2017); and (3) V90 is
de e minable du ing a submaximal es , i.e., maximal exe ion
is no always necessa y (Ga cia-Taba e al., 2017), wha makes
V90 some imes mo e sui able han PTV and ˙
VO2max. Resul s
indica e V90 o be an appealing a iable since i is a alid, easy,
nonin asi e and low-cos sui able es ima o o VMLSS and FBLC
h esholds du ing a p og essi e unning es in endu ance ained
unne s acili a ing he moni o ing o ae obic condi ioning.
Du ing exe cise a VMLSS, absolu e HR ma kedly di e ed
be ween subjec s. A e age ela i e HR (%HRmax), ins ead, was
main ained wi hin a easonably na ow ange o e ime (85–
92% om min 5 o 30), al hough, in ag eemen wi h o he
s udies in unne s (Ha e y e al., 1988; Llodio e al., 2016), i
also signi ican ly inc eased o e ime (Figu e 3). This sugges s
ha a HR zone, a he han a ixed absolu e o ela i e HR
alue, should be conside ed du ing aining sessions when
he goal is o each an exe cise in ensi y ela ed o VMLSS.
Howe e , he indi idual %HRmax alues du ing VMLSS CVRTs
a ied conside ably be ween indi iduals, anging om 81 o
85% HRmax and om 85 o 98% HRmax a e 5 and 30 min
o exe cise, espec i ely. This indica es ha he HR zone
co esponding o MLSS should be es ima ed on indi idual basis
(Llodio e al., 2016). An in e es ing inding was he ex emely
la ge ela ionship obse ed be ween he indi idual absolu e
HRLEmin and he indi idual absolu e HR alues a e 5 min a
VMLSS (Figu e 6). This associa ion sugges s ha HRLEmin can
be accu a ely used o p edic HR alue a e 5 min a VMLSS.
De e mina ion o VLEmin and i s co esponding HR is he e o e
F on ie s in Physiology | www. on ie sin.o g 9July 2018 | Volume 9 | A icle 1034
