Age and Activity Status Affect Muscle
Reoxygenation Time after Maximal
Cycling Exercise
SHIRO ICHIMURA1,2, NORIO MURASE2, TAKUYA OSADA2, RYOTARO KIME2, TOSHIYUKI HOMMA3,CHIHOKO UEDA2, TAKESHI NAGASAWA4, MAYUKO MOTOBE5, TAKAFUMI HAMAOKA2,6,
AND TOSHIHITO KATSUMURA2
1

Department of Liberal Arts, Faculty of Science and Technology, Tokyo University of Science, Chiba, JAPAN; 2Departmentof Preventive Medicine and Public Health, Tokyo Medical University; Tokyo, JAPAN; 3Department of Sports Sciences,
Japan Institute of Sports Sciences, Tokyo, JAPAN; 4Department of Integrated Arts and Science, Okinawa National College
of Technology, Okinawa, JAPAN; 5Department of Pediatrics, Tokyo Medical University; Tokyo, JAPAN; and 6Departmentof Sports Performance, National Institute of Fitness and Sports in Kanoya, Kagoshima, JAPANABSTRACTICHIMURA S., N. MURASE, T. OSADA, R. KIME, T. HOMMA, C. UEDA, T. NAGASAWA, M. MOTOBE, T. HAMAOKA, andT. KATSUMURA. Age and Activity Status Affect Muscle Reoxygenation Time after Maximal Cycling Exercise. Med. Sci. Sports
Exerc., Vol. 38, No. 7, pp. 1277– 1281, 2006. Purpose: The purpose of this study was to determine the interaction of age and habitualphysical activity on recovery time of muscle oxygenation following maximal cycling exercise (CycEXmax). Methods: Twelve
sedentary middle-aged (50 T 6), 13 sedentary elderly (66 T 3), 13 active middle-aged (53 T 5), and 20 active elderly (67 T 5) womenparticipated in this study. We evaluated the peak pulmonary oxygen uptake (V̇O2peak) during CycEXmax and the half-recovery timeof muscle oxygenation (T1/2reoxy time) using near-infrared spectroscopy at the vastus lateralis (VL) during the recovery phase after
CycEXmax. Results: T1/2reoxy time was significantly greater in the elderly subjects than in the middle-aged subjects in bothsedentary (P G 0.05) and active groups (P G 0.01). T1/2reoxy time of the active group was lower (P G 0.01) than that of the sedentarygroup regardless of age. Age was significantly correlated to T1/2reoxy time in both sedentary and active groups (in both sedentary andactive groups: P G 0.01). The slope of T1/2reoxy time against age in the sedentary group was significantly greater (VL: P G 0.05) thanthat of the active group. V̇O2peak showed significant inverse correlation with T1/2reoxy time at the VL in both sedentary and active
groups. The slope of V̇O2peak against T1/2reoxy time showed no significant differences between middle-aged and elderly subjects.
Conclusion: The results of this study suggest that T1/2reoxy time was prolonged with aging, regardless of habitual physical activity
levels. However, habitual physical activity may prevent the age-related prolongation in T1/2reoxy time after CycEXmax. V̇O2peak
appears to be one of the major factors determining T1/2reoxy time, not age. Key Words: AGING, HABITUAL PHYSICALACTIVITY, SEDENTARY WOMEN, ACTIVE WOMEN, NEAR-INFRARED SPECTROSCOPY, V̇O2peak

M

Recently, muscle oxygenation during exercise has beenmeasured noninvasively by near-infrared spectroscopy (15).
Muscle oxygenation measured by near-infrared spectroscopy
reflects the balance of O2 delivery to working muscles andmuscle O2 consumption in capillary beds (15). Recovery
time of muscle oxygenation following the completion of
exercise is used as an index of deficits of O2 delivery to themuscle in relation to O2 demand of the working muscle (2).
It is thought that recovery time of muscle oxygenation is anindicator for evaluating muscle aerobic function. In previous
studies, recovery time of muscle oxygenation after submaximal exercise has successfully been used to noninvasively andqualitatively assess muscle oxygenation kinetics in patientswith peripheral vascular disease (14). These data suggested
that recovery time of muscle oxygenation after submaximal
exercise is considered mainly dependent on O2 delivery tomuscles (10,14).
Kutsuzawa et al. (10) demonstrated that recovery rate ofmuscle oxygenation rate after submaximal handgrip exercise
was delayed with increased age. Furthermore, Hamaoka et al.
(8) suggested that recovery time of muscle oxygenation after

uscle volume (5), muscle oxidative capacity (5,13),and blood flow to working muscle (1,21) declinewith aging. Recently, it has been shown thatmuscle oxidative capacity and muscle blood flow after exercise to fatigue is higher in trained elderly people than insedentary peers (4,12). Endurance training has restored or
improved the muscle oxidative capacity and blood flow toworking muscles even in elderly people (1,3). The age/
activity-related changes in these muscle functions contributeto the changes in systemic aerobic capacity.

Address for correspondence: Shiro Ichimura, Department of Liberal Arts,
Faculty of Science and Technology, Tokyo University of Science, 2641
Yamazaki, Noda-shi, Chiba 278-8510 Japan; E-mail; shiro@rs.noda.tus.ac.jp.
Submitted for publication July 2005.
Accepted for publication February 2006.
0915-9131/06/3807-1277/0
MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ
Copyright Ó 2006 by the American College of Sports Medicine
DOI: 10.1249/01.mss.0000227312.08599.f1

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submaximal cycling exercise was shorter in athletes than in
their sedentary peers. To our knowledge, however, interaction of age and habitual physical activity on recovery timeof muscle oxygenation after maximal cycling exercise(CycEXmax) has not been established. Further, the relation
between systemic aerobic capacity and recovery time ofmuscle oxygenation after CycExmax is not clear. Therefore,
the purpose of this study was to determine the interactionof age and habitual physical activity on recovery time ofmuscle oxygenation and the relation of systemic aerobic
capacity and recovery time of muscle oxygenation following
CycEXmax. We hypothesized that habitual physical activity
may attenuate the age-related prolongation in recovery timeof muscle oxygenation and that systemic aerobic capacity isrelated to recovery time of muscle oxygenation immediately
after CycEXmax.

FIGURE 1—Typical kinetics of Hb/MbO2 and method of evaluating
T1/2reoxy time. Method to evaluate T1/2reoxy time, the time required
to reach the value halfway between the Hb/MbO2 level immediately
after exercise and that at peak hyperemia during recovery.

METHODS
Subjects. Thirty-three healthy active women (40Y67 yrold) and 25 healthy sedentary women (40Y76 yr old)participated in this study. For at least the previous 6 months,
subjects were either sedentary (no regular physical activity)or active (light- to moderate-intensity water exercise once or
twice per week). In addition, these subjects were divided into
sedentary middle-aged (N = 12), sedentary elderly (N = 13),
active middle-aged (N = 13), and active elderly (N = 20)
subgroups. All subjects were healthy and free of hypertension, diabetes, and cardiovascular disease as assessed bytheir medical history. Additionally, subjects currently on
pharmacotherapies with known vascular effects were excluded. All subjects gave their written informed consent
using the Tokyo Medical University Hospital institutional
review boardYapproved forms to participate. All procedures
were performed according to the Declaration of Helsinki.
Exercise test. Subjects performed a maximal aerobic
exercise test using a bicycle ergometer (Corval Load). The
physician determined an exercise load of 10 or 15 WIminj1
by ramp method in consideration of the subject_s age andweight. Pedal frequency was 60 rpm. The exercise test end
point was determined as the point when the rhythm of themetronome and the leg movement were not synchronized.
Measurements. During the exercise test, pulmonary
oxygen uptake (V̇O2peak AE-300 Minato, JAPAN) using
breath-by-breath basis, heart rate, and blood pressure were
measured. Additionally, oxygenated hemoglobin/myoglobin(Hb/MbO2) kinetics of the vastus lateralis (VL) were measured at the position two thirds of the way from the superior
end patella to greater trochanter of the thigh using nearinfrared continuous-wave spectroscopy (NIRcws; HEO-200
Omron, JAPAN). During the recovery phase immediately
after exhaustion, the half-recovery time of Hb/MbO2 (T1/
2reoxy time) (2,14) was measured. T1/2reoxy time wasdetermined as the time for 50% reoxygenation of Hb/MbO2
from the exhaustion level to the peak level. We showed thecalculation method of T1/2reoxy time in Figure 1.
Hb/MbO2 measured by NIRcws can be described by themathematical equation using Fick’s Law (22). Hb/MbO2,
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Official Journal of the American College of Sports Medicine

measured by NIRcws, reflects the balance of O2 delivery to
working muscles and muscle O2 consumption and indicates
the O2 content in the capillary bed (15). Thus, Hb/MbO2
measured by NIRcws can be expressed with the following
simple mathematical equation:
Hb=MbO2 ðCvO2 Þ ¼ CaO2 j V O2 mus=O2 delivery

where CaO2 is the O2 content at the beginning of thecapillary and CvO2 is the O2 content at the venous side of
the capillary (measurement site by NIRcws). V̇O2mus andO2 delivery are muscle O2 consumption and O2 delivery tomuscle, respectively. Therefore, faster Hb/MbO2 recovery
measured by NIRcws during recovery from exercise shouldbe the consequence of a faster recovery in V̇O2mus, or ahigher O2 delivery and/or slower recovery in O2 delivery, orboth of them. In contrast, a slower recovery in V̇O2mus or alower O2 delivery and/or faster recovery in O2 delivery
following exercise should elicit the delay of T1/2reoxy time
during the recovery phase following exercise. Thus, T1/
2reoxy time was used as an indicator for muscle aerobic
function (2,10,14,22).
The theoretical basis and principle of the NIRcws device
were discussed extensively in previous studies (15). In thisstudy, we used the NIRcws device with wavelengths of 760
and 850 nm. This device consists of a probe and acomputerized control unit, and the probe consists of a lightsource and an optical detector. The distance between thelight source and optical detector was 3 cm. The data sampling rate was 2 Hz.
Statistics. Descriptive data were presented as the mean
and SD for each group. A two-way analysis of variance(ANOVA) with post hoc comparisons was used to assess theeffects of age and habitual physical activity on the measured
variables. Linear correlation analysis or exponential curve
correlation analysis was used to assess the relationship between the variables. When a significant exponential curve correlation was found, a logarithmic conversion was executed on
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the variables to examine an analysis of covariance(ANCOVA). ANCOVA was performed to test the difference
between the middle-aged and elderly subjects or between
active and sedentary groups in terms of dependent variableadjusted by independent variable when a significant linear
correlation was found between the variables. Statistical significance was set a priori at P G 0.05.

RESULTS
Comparison between middle-aged and elderly
subjects. Peak workload and V̇O2peak were significantly
lower (P G 0.01) in the elderly subjects than those of the
middle-aged subjects in the active group, but not significantly different between ages in the sedentary group.
HRpeak was significantly lower in the elderly subjects
compared with the middle-aged subjects in both sedentary
and active groups (sedentary group: P G 0.05; active group:
P G 0.01). T1/2reoxy time was significantly greater in theelderly subjects compared with the middle-aged subjects
within the same physical activity group (sedentary groups:
P G 0.05; active group: P G 0.01).
Comparison between sedentary and active
groups. Peak workload in the sedentary group was
significantly lower than that of the active group only inthe middle-aged subjects (P G 0.01). The differences inhabitual physical activity did not influence HRpeak within
subjects of the same age. V̇O2peak in the sedentary groupwas significantly lower compared with the active group, regardless of age (both elderly and middle-aged subjects:
P G 0.01). The sedentary group showed a significantly greater
T1/2reoxy time than the active group of the same generation(both elderly and middle-aged subjects: P G 0.01).
The relationship between age and t1/2 reoxy
time. Figure 2 shows the relationship between age and T1/
2reoxy time. The T1/2reoxy time was positively related to age
in both sedentary (r = 0.663, P G 0.001) and active (r = 0.498,
P G 0.01) groups. The slope of T1/2reoxytime against age

FIGURE 2—The relationship between age and T1/2reoxy time insedentary and active groups. The slope of age-related prolongation in
T1/2reoxy time was significantly lower in the active group than in thesedentary group (* P G 0.05 for both VL and LG).
RECOVERY TIME OF MUSCLE OXYGENATIONFIGURE 3—The relationship between V̇O2peak and T1/2reoxy time in
middle-aged and elderly subjects. The logarithm slope of V̇O2peak andT1/2reoxy time showed no significant differences between middleaged and elderly subjects.

was significantly greater in the sedentary group (0.94 sIyrj1)
than in the active group (0.44 sIyrj1) (P G 0.05).
The relationship between V̇O2peak and T1/2reoxy
time. Significant exponential curve correlation was foundbetween V̇O2peak and T1/2reoxy time. Figure 3 shows thelogarithmic graph of relationship between V̇O2peak and T1/
2reoxy time. There was an inverse correlation between
V̇O2peak and T1/2reoxy time in both middle-aged (r =j0.835, P G 0.001) and elderly subjects (r = j0.852, P G
0.001). The logarithm slope of V̇O2peak and T1/2reoxy time
showed no significant differences between middle-aged
and elderly subjects (Fig. 3).

DISCUSSION
Primary findings of this cross-sectional study are as follows.
First, T1/2reoxy time was significantly related to age, and T1/
2reoxy time was greater in the elderly subjects than in the
middle-aged subjects, regardless of habitual physical activity
levels. Second, T1/2reoxy time was lower in the active groupthan in the sedentary group in both middle-aged and elderly
subjects (Table 1). The slope of T1/2reoxy time against age
was significantly lower in the active group than in the sedentary group (Fig. 2). Third, V̇O2peak and T1/2reoxy time
was inversely correlated, and the logarithm slope of V̇O2peak
and T1/2reoxy time showed no significant differences
between middle-aged and elderly subjects (Fig. 3). Fromthese findings, we suggest that habitual physical activity may
attenuate age-related prolongation in T1/2reoxy time inworking muscles. V̇O2peak appears to be one of the major
factors determining T1/2reoxy time, not age.
Age-related prolongation in T1/2reoxy time. In
this study, there was age-related prolongation in T1/2reoxy
time in both the sedentary and active groups, respectively.
This result was in agreement with the findings of a previous
study (10) in which recovery rate of muscle oxygenation measured in the forearm flexor muscles was not in agreement
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TABLE 1. Influences of age and physical activity status on oxygen consumption, heart rate, workload, and T1/2reoxy time during peak exercise.
ActiveV̇O2peak (mLIkgj1Iminj1)
HRpeak (bpm)
Peak load (W)V̇O2IWj1) (mLIkgj1Iminj1IWj1)
T1/2reoxy time (s)Sedentary

Middle-Aged

Elderly

Middle-Aged

Elderly

33.1 T 3.9
163.5 T 9.6
143.0 T 21.8
0.23 T 0.05
22.5 T 3.3

24.7 T 4.0**
149.9 T 13.5**
101.1 T 22.6**
0.25 T 0.05
29.6 T 8.9*

21.9 T 3.7##
157.3 T 11.5
108.9 T 34.8##
0.21 T 0.04
35.7 T 9.0##

19.7 T 4.4##
145.2 T 18.4*
88.5 T 24.9
0.23 T 0.04
45.7 T 13.6*,##

Values are mean T SD.
* P G 0.05 vs middle-aged group of same physical activity status; ** P G 0.01 vs middle-aged group of the same physical activity status; ## P G 0.01 vs active group of age-matched group.

with the result for which half-recovery time of muscle oxygenation was measured in vastus lateralis after exhaustive
cycling exercise (6). Costes et al. (6) reported that there wasno significant difference in recovery time of muscle oxygenation after exhaustive cycling exercise in young (33.5 T
17.5 s) and elderly (28.2 T 10.5 s) subjects. Costes’s elderly
subjects were engaged in recreational physical activities, andyoung subjects ranged from sedentary to moderately trained.
Thus, physical activity status between young and elderly
subjects was inconsistent. In addition, the variation of halfrecovery time of muscle oxygenation appears larger in theyoung subjects than in the elderly subjects partly because
physical activity status among the young subjects was varied.
A wide variety of physical activity status may cause a discrepancy of age-related change in T1/2reoxy time between
this study and the previous study (6). Therefore, physicalactivity status would be expected to play an important role indetermining the extent to which muscle aerobic functionchanges with increased age.
It is reported that advanced age impairs vascular function(7,9) and peak blood flow to the working muscles (21).
Muscle oxidative capacity declines with increased age (5,13).
It is thought that because muscle oxygenation kinetics
measured by NIRcws after exercise are controlled byrecovery speed of muscle O2 consumption and O2 delivery
to muscle after exercise, a slower recovery of V̇O2mus and/or lower O2 delivery after exercise with increased age resultsin the prolongation of T1/2reoxy time during recovery
following exercise. The results of previous studies having
reported age-related decline in blood flow to muscle, peripheral vascular function, and structure, and muscle oxidative
capacity may support the age-related prolongation in T1/
2reoxy time for the sedentary and active groups found in thisstudy. We suggest that age-related prolongation in T1/2reoxy
time in working muscles reflects the age-related decline inmuscle aerobic function.
Activity-related change in T1/2reoxy time. T1/
2reoxy time was significantly lower in the active group thanin the sedentary group for both middle-aged and elderly
subjects. The slope of T1/2reoxy time against age wassignificantly smaller in the active group than in the sedentarygroup. In a previous study, T1/2reoxy time in working
muscles after sub-maximal cycling exercise was lower inyoung athletes than in their sedentary peers (8). From theseresults, we suggest that habitual physical activity can attenuate the age-related prolongation in T1/2reoxy time inworking muscles.
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In cross-sectional studies, peak cardiac output (19), bloodflow to working muscles (1,20) during peak exercise, andmuscle oxidative capacity (4) were greater in active subjects
than in sedentary subjects in both young and elderly subjects. It has been demonstrated that the blood flow to working muscles (1) during peak exercise, vascular functions(7,23), and muscle oxidative capacity (3) improve when
physical activity was sufficient. Thus, the results of previous
studies, having reported that habitual physical activity can
prevent the age-related decline in peak blood flow andmuscle oxidative capacity, support the attenuated agerelated prolongation in T1/2reoxy time in working musclesin the active group found in this study.
Relationship V̇O2peak and T1/2reoxy time. In thisstudy, V̇O2peak was significantly related to the T1/2reoxy
time in both middle-aged and elderly subjects. Previous
studies have reported that high V̇O2peak was associated withprolongation of the vasodilation duration after arterial occlusion with calf exercise (9), elevated peak vascular conductance after exercise (12), and a faster recovery of PCr
measured by 31P magnetic resonance spectroscopy (31PMRS) after exercise (11). Muscle microvascular oxygenpressure (PO2), a reflection of the balance between O2delivery to working muscles and muscle O2 consumption,
can be a similar indicator to Hb/MbO2 measured by NIRcws.
It was reported that PO2 recovery following muscle contractions was faster in highYoxidative-capacity muscle(16Y18). Results of these previous studies support that T1/
2reoxy tine after exercise evaluated by NIRcws can be anindex of muscle aerobic function, including muscle O2
utilization and muscle O2 delivery.
The slope between V̇O2peak and T1/2reoxy time and theintercept to the y-axis showed no significant differences
between middle-aged and elderly subjects. These results do
not distinguish whether an increase in muscle aerobic
function improves the systemic aerobic capacity, or
whether the improvements of muscle aerobic function andsystemic aerobic capacity occur simultaneously. However,
the results do indicate that the systemic aerobic capacity isrelated to muscle aerobic function evaluated by T1/2reoxy
time, and the relationship between systemic aerobic
capacity and T1/2reoxy time is similar between middleaged and elderly women. Thus, V̇O2peak, but not age, may
be one of the major factors determining T1/2reoxy time.
Limitations. A limitation of this study is its crosssectional design. We did not monitor or control the daily
physical activity level and the intensity during water exercise
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in individuals of the active group, although individuals of theactive group had participated in the same water exercise
course. In this study, V̇O2peak and peak load showedsignificant differences between middle-aged and elderly
subjects in the active group but not in the sedentary group.
Thus, it is speculated that the difference in physical activity
level between the middle-aged subjects and elderly subjects
in the active group may be larger than that of the middleaged subjects and elderly subjects in the sedentary group.
Thus, environmental factors including daily physical activity
level as well as genetic or other constitutional factors may
have influenced this cross-sectional study. To further
understand the effect of habitual physical activity on agerelated prolongation in recovery time of muscle oxygenation

in working muscles, it is important to lessen the variationof physical activity level within a similar physical activity
status, and longitudinal studies are needed.
In conclusion, habitual physical activity may attenuate
age-related prolongation in T1/2reoxy time in working
muscles. V̇O2peak appears to be one of the major factors
determining T1/2reoxy time, not age.

We would like to thank the entire staff of the Department ofPreventive Medicine and Public Health, Tokyo Medical University,
especially Aya Kitahara, Yuko Kurosawa, Naoki Nakagawa, Eric
Sell, Kathryn Kempf, Christa Colletti, and Kiyoshi Shiroishi for their
excellent collaboration in this investigation.

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