CHAPTER 8 • BASICS IN EXERCISE PHYSIOLOGY 43Hb-O 2 affinity. Peripheral determinants include
muscle blood flow, capillary density, O 2 diffusion to
and extraction by muscle cells, Hb-O 2 affinity, and
skeletal muscle fiber profiles.AEROBIC AND ANAEROBIC EXERCISE
EXERCISEDOMAINS
- Three specific exercise domains were reported by
Gaesser and Poole (1996). Graphical presentations of
the domains (moderate, heavy, and severe) are pre-
sented in Fig. 8-4 for an incremental exercise test and
for constant load tests at three workloads. In panel
one, the lactate threshold(TLac) represents the bound-
ary between the moderate and heavy domain, and
critical power (Wa) represents the boundary for the
severe domain. These concepts are described below. - Lactate threshold:As shown in Fig. 8-4, TLacrepre-
sents the lowest exercise intensity that can be main-
tained where blood lactate appearance exceeds its
removal and there is a sustained increase of about
1 mM lactates above preexercise levels. - Maximal lactate at steady state:Maximal lactate at
steady state(MLSS) is the highest blood lactate con-
centration that can be sustained without progressive
accumulation: a new steady state is achieved (between
3 and 8 mM). The upper boundary of the heavy
domain may demarcate MLSS. - Critical power:As the lower boundary of the severe
domain, Wa is the maximum power output that can be
sustained without a continued and progressive anaero-
bic contribution. Exercise above Wa will elicit VO2max.- Onset of blood lactate accumulation:At specific
exercise intensity, muscle lactate production exceeds
utilization and blood lactate begins to accumulate
because appearance exceeds removal. Wa, MLSS, and
onset of blood lactate accumulation (OBLA) may all
demarcate the transition between the heavy and severe
exercise domains. - Steady state exercise:When rate of lactate produc-
tion is balanced by the rate of oxidative removal and
VO 2 is stabilized within 3 to 6 min. As such, cardiac
output, HR, and pulmonary gas exchange are in a
steady state and exercise can continue for an extended
period of time. - Slow component of oxygen uptake:A continued rise
in VO 2 beyond the 3rd min is observed when exercise is
above the lactate threshold. The rise in VO 2 (Fig. 8-4)
usually stabilizes within 20 min when exercise is within
the heavy domain, or gradually increases to VO2max
when exercise is within the severe domain. The cause of
the slow component of oxygen uptake has not been
clearly defined, but may reflect that the working limbs
are a key to initiation of this rise in VO 2.
- Onset of blood lactate accumulation:At specific
OXYGENKINETICS- Oxygen deficit:When an individual begins to exer-
cise, a certain VO 2 is required but the aerobic energy
system cannot meet the demands aerobically. VO 2
gradually increases until it reaches a steady state. The
difference in VO 2 between steady state O 2 and O 2
required but not used prior to steady state conditions
is termed the O 2 deficit. - Oxygen debt: On termination of exercise, VO 2
remains elevated to restore energy systems to their
FIG. 8-4 The VO 2 responses to incremental exercise (left panel), and the VO 2 (middle panel) and
blood lactate (right panel) responses to constant load exercise as a function of exercise intensity
domains. TLacrepresents the lactate threshold and Wa represents critical power or work rate where
maximal lactate at steady state occurs. (Reprinted with permission, DA Poole [Poole and
Richardson, 1997; Gaesser and Poole, 1996]).