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Introduction: The Moxy is a novel, cutaneously placed muscle oxygen monitor which claims to measure local oxygen saturation (SmO2) and total haemoglobin (THb) using near-infrared spectroscopy. If shown to be reliable, its data storage and telemetric capability will be useful for assessing localised O2 usage during field-based exercise. This study investigated the reliability of the Moxy during cycling and assessed the correlations between its measurements, whole-body O2 consumption (VO2) and heart rate (HR). Methods: Ten highly trained cyclists performed an incremental, step-wise cycling protocol on two occasions while wearing the Moxy. SmO2, THb, VO2 and HR were recorded in the final minute of each five-minute stage. Data were analysed using Spearman's Order-Rank Coefficient (SROC), Intraclass Correlation (ICC), and Coefficient of Variance (COV). Significance was set at p ≤ .05. Results: SmO2 showed a 'strong' or 'very large' correlation between trials (SROC: r = 0.842-0.993, ICC: r = 0.773-0.992, p ≤ .01) and was moderately correlated with VO2 and HR (r = -0.71-0.73, p ≤ .01). SmO2 showed a moderate to high reliability at low intensities, but this decreased as relative exercise intensity increased. THb showed poor correlations between tests and with the other measured variables, but was highly reliable at all power outputs. Conclusions: The Moxy is a reliable device to measure SmO2 at low to moderate intensities, but at higher intensities, greater variation in measurements occurs, likely due to tissue ischaemia or increased movement artefacts due to more frequent muscular contractions. THb has low variation during exercise, and does not appear to be a valid indicator of muscle oxygenation.
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European Journal of Sport Science
ISSN: 1746-1391 (Print) 1536-7290 (Online) Journal homepage:
Validity and reliability of the Moxy oxygen monitor
during incremental cycling exercise
E. M. Crum , W. J. O’Connor, L. Van Loo, M. Valckx & S. R. Stannard
To cite this article: E. M. Crum , W. J. O’Connor, L. Van Loo, M. Valckx & S. R. Stannard (2017):
Validity and reliability of the Moxy oxygen monitor during incremental cycling exercise, European
Journal of Sport Science, DOI: 10.1080/17461391.2017.1330899
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Published online: 30 May 2017.
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Validity and reliability of the Moxy oxygen monitor during incremental
cycling exercise
School of Sport and Exercise, Massey University, Palmerston North, New Zealand &
Haagsche Hogeschool, Den Haag,
Zuid-Holland, Netherlands
Introduction: The Moxy is a novel, cutaneously placed muscle oxygen monitor which claims to measure local oxygen
saturation (SmO
) and total haemoglobin (THb) using near-infrared spectroscopy. If shown to be reliable, its data storage
and telemetric capability will be useful for assessing localised O
usage during field-based exercise. This study investigated
the reliability of the Moxy during cycling and assessed the correlations between its measurements, whole-body O
consumption (VO
) and heart rate (HR). Methods: Ten highly trained cyclists performed an incremental, step-wise
cycling protocol on two occasions while wearing the Moxy. SmO
, THb, VO
and HR were recorded in the final minute
of each five-minute stage. Data were analysed using Spearmans Order-Rank Coefficient (SROC), Intraclass Correlation
(ICC), and Coefficient of Variance (COV). Significance was set at p.05. Results: SmO
showed a strongor very
largecorrelation between trials (SROC: r= 0.8420.993, ICC: r= 0.7730.992, p.01) and was moderately correlated
with VO
and HR (r=0.710.73, p.01). SmO
showed a moderate to high reliability at low intensities, but this
decreased as relative exercise intensity increased. THb showed poor correlations between tests and with the other
measured variables, but was highly reliable at all power outputs. Conclusions: The Moxy is a reliable device to measure
at low to moderate intensities, but at higher intensities, greater variation in measurements occurs, likely due to
tissue ischaemia or increased movement artefacts due to more frequent muscular contractions. THb has low variation
during exercise, and does not appear to be a valid indicator of muscle oxygenation.
Keywords: Exercise, training, technology, physiology
.The Moxy monitor is a small, lightweight device with data capture capacity, which claims to measure local muscle oxygen
saturation (SmO
) and haemoglobin content (THb) using near-infrared spectroscopy.
.The Moxy showed strong correlations between SmO
values during two repeated cycling exercise protocols, conducted
one week apart, however, the reliability of values decreased as the exercise intensity increased.
.THb values showed low variation during exercise of varying intensity and did not appear to be a valid indicator of muscle
The Moxy muscle oxygen monitor is a small (dimen-
sions: 61 × 44 × 21 mm) lightweight (42 g)
cutaneously placed device which claims to measure
local oxygen saturation (SmO
) and total haemo-
globin (THb) in the muscle capillaries below its
point of position using near-infrared spectroscopy
(NIRS). NIRS models were developed as a non-inva-
sive method for measuring localised blood flow and
oxygenation, as opposed to the global measurements
of flow provided by earlier Doppler and plesthsmo-
graphy devices. The process is based on the differen-
tial proportion of wavelengths which are absorbed by
oxygenated and deoxygenated Hb (De Blasi, Cope,
Elwell, Safoue, & Ferrari, 1993; Jobsis, 1977).
However, traditional models are bulky and often
require multiple wire attachments to an external
device. Though suitable for research in a laboratory,
© 2017 European College of Sport Science
Correspondence: E. M. Crum, School of Sport and Exercise, Massey University, Corner University Ave and Albany Drive, Palmerston
North, New Zealand. E-mail:
Data were collected by LV and MV with the help of EC and WO. Data analysis was performed by LV and MV. The study was written up by
EC with the help of WO and SS. All authors read and approved the final manuscript.
European Journal of Sport Science, 2017
such products are limited in their use in field-based
studies. Thus, devices such as the Moxy, which
have data storage and telemetric capability, have the
potential to expand current knowledge of muscle
usage in real-lifesporting situations and field-
based research.
In addition, the Moxy manufacturers claim that
their product will make local O
monitoring more
accessible to the general athletic population, and as
such provide a new method for measuring training
intensity zones. These zones can be used to guide
training prescription via the effect of a particular
mechanical workload on muscle O
as opposed to using pace, power or heart rate (HR),
which are influenced by environmental conditions,
fatigue or mental stress. Further, the return of oxy-
genation values to a pre-determined plateau may
help determine the length of recovery between inter-
vals, or the number of intervals that should be per-
formed in a session (Fortiori Design LLC, 2015).
However, although the validity of the NIRS
method has been demonstrated through its highly
significant correlations with venous O
at rest and during exercise (r= 0.92) (Mancini
et al., 1994), and from the reproducibility of its
measurements during repeated incremental
running (r= 0.870.88) and cycling (r= 0.940.99)
tests to exhaustion (Austin et al., 2005), there is
little published information regarding the reliability
of the Moxy. This raises the question of whether it
is reliable enough to be used in scientific research
or in the monitoring of training. The group of
Born, Stöggl, Swarén, and Björklund (2016)
demonstrated that the MoxysSmO
inversely correlates with VO
(r=0.7) during trail
running on hilly terrain. In addition, Cornachione,
McLaren, and Heil (2014) reported that SmO
measurements during various skiing styles changed
in response to intensity, location of the sensor
(arm versus leg placement) and variation of skiing
movement (arm versus leg-dominant). However,
neither study used replicated trials, so no evaluation
of the reproducibility of results obtained from the
Moxy could occur.
The current study thus aims to determine whether
data obtained from the Moxy during cycling testing
protocols can be replicated in subsequent identical
trials performed one week later by the same partici-
pants. In addition, we investigated whether the
Moxy can successfully monitor effort by determining
whether its measures correlate with other physiologi-
cal indicators of exercise intensity (HR, VO
Because it uses the previously validated NIRS
method, it is hypothesised that the Moxy measure-
ments will show strong correlations and reliability
between trials, and with HR and VO
Ten highly trained cyclists, including nine males and
one female, were recruited from the local cycling and
triathlon communities. The participants were all
regular competitors in local cycling events and had
an average age, height and weight of 23 years
(range: 1630), 180 ± 9 cm and 71 ± 10 kg. All par-
ticipants provided written consent after being
informed about the nature of the experiment and
completed a health questionnaire to determine their
suitability for the study. The study was approved by
the Massey University Human Ethics Committee
(Southern A: 16/21) in accordance with the Declara-
tion of Helsinki.
The Moxy device
A diagram of the Moxy monitor is shown in Figure 1.
As with earlier NIRS devices, the Moxy monitor
(Moxy, Fortiori Design LLC, Minnesota, USA)
functions by sequentially sending light waves (630
850 nm) from four light emitting diodes into the
tissue beneath it and recording the amount of
returned scattered light at two detectors positioned
12.5 and 25 mm from the light source. The pen-
etration depth of the light received at each detector
is half the distance between the light source and the
detector. The scattered light is processed by an algor-
ithm, which combines a tissue light propagation
model and the BeerLambert law to determine the
amount of light absorbed at wavelengths pertaining
Figure 1. Placement of the Moxy monitor.
2E. M. Crum et al.
to oxygenated and deoxygenated Hb. This allows cal-
culation of THb present beneath the device, as well as
the percentage of Hb containing O
). Because
light passing into micro-vessels with a diameter
greater than 1 mm is expected to be completely
absorbed, it is assumed that the majority of reflected
light comes from the capillaries, and thus the
measurements obtained reflect the relative supply of
to the muscle versus its uptake (Fortiori Design
LLC, 2015; McCully & Hamaoka, 2000).
Experimental protocol
Each participant completed a bout of cycling exercise
protocol on two occasions separated by seven days.
Both trials were completed at the same time of day
and in the same air-conditioned lab which was set
to 17°C to ensure consistency across all trials. Partici-
pants were asked to refrain from heavy exercise in the
24 hours prior to each trial, and any exercise that was
completed during this period prior to the first trial
was replicated before the second trial. All participants
had previously been involved with research in our lab-
oratory and were familiar with the equipment and
testing protocols employed, thus a familiarisation
session was not required.
Pre-exercise protocol
On arrival into the laboratory, body mass was
obtained and a HR monitor (Polar Electro,
Kempele, Finland) was applied. The Moxy was posi-
tioned on the participants dominant leg, on the
vastus lateralis, halfway between the greater trochan-
ter and lateral epicondyle of the femur. The vastus
lateralis was chosen as the location for the Moxy
because it is part of the knee extensor group which
is the primary contributor to force generation in the
crank of the bicycle during down stroke of the pedal
(Raasch, Zajac, Ma, & Levine, 1997). Prior to place-
ment, this area was trimmed with an electric razor
and cleaned with alcohol swabs. The device was
secured with a light shield and athletic tape to block
ambient near-infra red light from interfering with
the detectors, and its exact position was recorded
and replicated for the second trial. After resting in a
seated position for five minutes, resting measures
for HR, SmO
and THb were recorded.
Exercise protocol
The cycling protocol was completed on an electroni-
cally braked cycle ergometer (Lode Excalibur, Gro-
ningen, the Netherlands) which was set up as
closely as possible to the participants own bike.
The set-up dimensions in the first trial were recorded
and replicated for the second trial. Following, the
pre-exercise measures, the participant mounted the
ergometer and completed a five-minute warm-up at
50 Watts (W). Subsequently, they completed a
step-wise protocol, which began at 100 W and
increased by 50 W every five minutes until exhaus-
tion. A step-wise protocol was chosen to allow assess-
ment of the Moxys reliability across a range of levels
of metabolic demand. During all stages, cadence was
kept at 90 rpm to ensure consistency between trials,
and exhaustion was defined as the inability to main-
tain this cadence or voluntary cessation of exercise.
This occurred after 46 stages (final stage = 250
350 W) depending on each individuals fitness level.
HR and Moxy data were recorded constantly
throughout the trial, with the average values from
the last minute of each stage being used for analysis.
There was also real-time monitoring of data using
PerfPRO computer software (Hartman Technol-
ogies, Rockware, Michigan, USA) which was dis-
played on a screen that was only visible to the
researchers. At 3:30 minutes into each stage, a
mouthpiece and nose-clip were applied to the partici-
pant and expired air was collected in a Douglas bag
for one minute. The expired gases in the Douglas
bags were immediately analysed for O
and carbon
dioxide (CO
) concentrations and volume using a
calibrated gas analysing system (AD Instruments,
Dunedin, New Zealand), which was calibrated
using gases of known concentration (15.01% O
5.01% CO
Data analyses
Minute ventilation (V
) and concentrations of O
and CO
values were used to calculate the volume
of inspired air (V
) using the Haldane transformation,
where V
was corrected for barometric pressure,
ambient temperature and atmospheric water satur-
ation. Subsequently, VO
and expired CO
could be determined and are reported as standard
temperature and pressure dry (STPD).
Statistical analyses
Average values for the data collected constantly
during the exercise (HR, SmO
, THb) were calcu-
lated for each minute of each trial and used in the
analyses described hereafter. Statistical analyses
were performed using statistical computer software
(SPSS Statistics, Version 23, IBM Corporation,
New York). Linear correlations were performed to
explore associations between the two trials. The
level of correlation between trials for the Moxy
Reliability of the Moxy oxygen monitor 3
variables (SmO
and THb) was determined using
Spearmans Rank-Order correlation (SROC; r=1
perfect correlation; >0.75 strong; >0.5 moderate;
<0.5 weak) and Intraclass Correlation (ICC; r=
>0.9 almost perfect correlation; 0.70.89 very large;
0.50.69 large; 0.30.49 moderate; 0.10.29 small;
<0.1 trivial). The reliability of the Moxy measure-
ments between trials was assessed using the coeffi-
cient of variation (COV) with the equation SD/
mean 100. The COV data from each participant
was pooled to determine an average COV for each
exercise stage. In accordance with Tew et al.
(2011), COVs of 10%, 1025% and >25% were
considered good, moderate and poor. To test for cor-
relations between the Moxy measures and other vari-
ables (VO
, HR, velocity, power), SROC was
performed and used for analysis as previously
described. A negative correlation value indicates an
inverse relationship between variables. Significance
was set at p.05.
Changes in physiological variables
Data detailing the changes in physiological variables
are presented in Table I. As exercise intensity
increased, there was a significant increase in HR
and VO
(p< .01), and a significant decline in
(p< .01). THb showed little variation
throughout each trial and was not significantly associ-
ated with changes in exercise intensity (p= .29).
Correlations and reliability between trials
A strong correlation for SmO
was observed in all
participants with SROC and ICC (SROC: 0.834
0.980; ICC: 0.7730.992). For the THb measure-
ments, six participants showed a weak correlation
(<0.5), two showed a moderate correlation (0.5
0.75) and two showed a strong correlation with
SROC (>0.75). For ICC, THb showed a moderate
correlation in one participant (0.482), but all other
participants showed a small (0.10.29) or trivial
(<0.1) correlation. Data detailing the reliability
between trials for SmO
is presented in Table II.
While COV demonstrated a good to moderate
reliability at lower relative exercise intensities,
reliability lessened as intensity increased. For THb
there was a strong reliability of 1% between tests
for all participants at all exercise intensities (Table
II) which corresponded to a day-to-day variation in
of 0.1 g dL
Correlations between Moxy measures and other
Data detailing the correlations between SmO
THb with VO
, HR and power output are presented
in Table III. These values represent the average
SROC value across the two trials. SmO
showed a
moderate inverse correlation with all other variables
(r=0.710.73, p< .01). VO
also showed a strong
correlation with HR (r= 0.83, p< .01). However,
THb did not correlate with any of the other measured
Table I. Average values for physiological variables measured during the exercise protocol.
100 W 150 W 200 W 250 W 300 W 350 W
52 ± 6 45 ± 936 ± 1126 ± 1120 ± 815 ± 6
THb 12.7 ± 0.2 12.7 ± 0.3 12.7 ± 0.3 12.7 ± 0.3 12.8 ± 0.3 12.7 ± 0.3
HR 112 ± 12 130 ± 14146 ± 17162 ± 17171 ± 14175 ± 14
27 ± 4 36 ± 545 ± 655 ± 764 ± 871 ± 9
Notes: Data are presented as mean ± SD. SmO
, muscle oxygen saturation expressed as %; THb, total haemoglobin content in g dL
; HR,
heart rate in bpm, VO
, whole-body oxygen uptake in ml min kg
p.05 compared to the previous stage.
Table II. Average coefficient of variation values between tests for
the Moxy measurements.
Power output (W) SmO
100 4 1
150 5 1
200 12 1
250 20 1
300 31 1
350 28 <1
Note: COV data are presented as %. SmO
, muscle oxygen
saturation; THb, total haemoglobin.
Table III. Correlations between Moxy measurements and other
measured variables.
0.05 0.730.71
THb 0.05 0.11 0.03
0.730.11 0.83
HR 0.710.03 0.3
Notes: SmO
, muscle oxygen saturation; THb, total haemoglobin;
, whole-body oxygen consumption; HR, heart rate; PO, power
p< .01.
4E. M. Crum et al.
This study was designed to determine whether the
Moxy is a reliable device to measure muscle oxygen-
ation characteristics (SmO
, THb) in the vastus later-
alis during incremental cycling exercise. The data
support the validity of the Moxy to measure SmO
with statistical analyses showing a strong or excellent
correlation between trials for all participants (SROC:
r= 0.8420.993, ICC: r= 0.7730.992, p< .01).
Further, SmO
measurements showed a moderate
negative correlation with VO
and HR (r=0.71
0.73, p< .01), indicating that this variable is an
acceptable index of metabolic demand in the
working muscle. However, while the reliability of
measurement was good or moderate at lower
intensities, this decreased as the relative exercise
intensity increased for each participant. In contrast,
the THb measurements showed a poor or weak cor-
relation in the majority of participants for both stat-
istical analyses and were not correlated with any
of the other physiological variables measured.
However, the reliability of THb measurements was
strong in every participant at all intensities.
The reliability of the SmO
measurements shown
in the current study combined with the compact
nature of the device and its data capture capacity,
suggest that the Moxy may be useful for measuring
changes in local muscle oxygenation characteristics
resulting from an intervention, environmental influ-
ences or changes in training state. While portable
devices exist to measure whole-body O
usage (Over-
street, Bassett, Crouter, Rider, & Parr, 2016), there
has previously been no convenient and portable
method of recording local muscle O
status. The
Moxy device is small enough to be worn without
encumbering most types of exercise and possess
data capture capability, so it will have some utility
in the field-based setting. Accordingly, the Moxy
has already been used to determine local muscle oxy-
genation in exercise modes which cannot be easily
conducted in a laboratory, such as trail running,
rock climbing and skiing (Born et al., 2016; Corna-
chione et al., 2014; Kodejska, Michailov, & Balas,
2015). The low COV values shown in the current
study during low to moderate exercise intensities cor-
responded to day-to-day variation in SmO
values of
5 units, while a moderate COV corresponded to
changes in SmO
values of 510 units. Although
the Moxy shows lower reliability at higher exercise
intensities, this is similar to the reliability pattern
found in measurements from more traditional
NIRS devices (Thiel, Vogt, Himmelreich, Hubscher,
& Banzer, 2011). Thiel et al. (2011) attributed the
lower reliability of NIRS measurements during
cycling exercise at 75% VO
compared to 25%
to the impairment of muscle perfusion by
stronger contractions producing more variable
tissue oxygenation. In addition, we suggest that
greater movement artefact which is likely to occur
with increased rates of muscular contraction, may
also contribute.
The moderate inverse correlation between SmO
and VO
(r=0.73) is in accordance with Born
et al. (2016) who found that the changes in SmO
in the vastus lateralis of elite runners competing in
an undulating trail running race closely corre-
sponded to changes in VO
. This inverse relation-
ship reflects the increasing difference between the
mean muscle capillary O
content and the rate of
utilisation by the working muscle. That is, as
the contracting muscle is asked to produce more
aerobic-derived power, its rate of O
uptake from
the blood supply increases. Since SmO
is a
measure of the mean localised muscle capillary
content, if more is being taken up by the muscle,
then the mean O
content of the capillaries perfusing
the muscle will decrease, as this includes inflow of
as well as outflow of CO
(Bhambhani, 2004).
Indeed the greater O
concentration gradient
between the two compartments drives the movement
of O
into the muscles at an increased rate. In
addition, the greater rate of mechanical work requir-
ing the greater VO
results in an increased concen-
tration of intramuscular adenine diphosphate,
which signals a need for more oxidative ATP pro-
duction and further promotes O
movement into
the muscle (Bassett & Howley, 2000).
Although the current study showed a moderate
inverse correlation between HR and SmO
0.71) and a strong correlation between HR and
(r= 0.83) during exercise on a stationary bike,
others (Born et al., 2016) could find no correlation
for HR with either measure in trail runners. In that
study HR did not correspond to changes in terrain,
but instead remained steady throughout the race.
Stationary cycling allows a controlled exercise
environment where HR is predominantly determined
by the amount of O
required to perform a particular
power output and its value is well correlated with
other indicators of O
usage. However, during trail
running, HR is also influenced by the significant
psychological input and impact forces which occur
during downhill running on steep and technical
terrain (Born et al., 2016). It is likely that in field-
based situations which often involve a number of
influencing factors on HR, SmO
is a more precise
indicator of metabolic demands than HR. This
gives support to the use of training zones based on
muscle oxygenation, rather than the more tradition-
ally used HR, when exercising in a field-based
Reliability of the Moxy oxygen monitor 5
In contrast to the reliability indicated for the SmO
measurements, the THb data showed a poor corre-
lation between the two tests and was not associated
with any other physiological measures. However,
despite being poorly correlated, THb measurements
showed a strong reliability between tests for all par-
ticipants at every intensity, which corresponded to a
day-to-day variation in values for a given stage of
0.1 g dL
. This may be explained by the very
small variation in THb values throughout each test
(average range across all stages: 0.2 g dL
), despite
large changes in all other measured variables. It is
likely that our highly trained participants had a suffi-
cient supply of oxygenated Hb to the muscles
throughout the test, and were not limited by a lack
of O
availability, even at higher intensities. The dif-
fusion of O
into the mitochondria is largely driven by
the O
concentration gradient between the intra and
extra-muscular capillaries, as well as a build-up of the
by-products produced in the formation of ATP.
Thus, with increased muscular O
the drive for O
diffusion into the muscles is
greater, decreasing the amount of O
in the capillaries
surrounding the muscles (SmO
) (Honig, Connett,
& Gayeski, 1992). In the current study, it appears
that this alteration in drive for O
diffusion was the
major determinant in O
usage, rather than an
increase in Hb transport. Consequently, THb does
not appear to be a valid way of indicating effort,
and SmO
may be a more relevant measure for moni-
toring changes in O
usage in highly trained athletes.
However, it is possible that due to their lower content
of Hb, the VO
of untrained individuals during pro-
gressive exercise may be influenced by THb to a
greater extent, leading to a greater correlation
between THb and other physiological variables
during exercise.
Despite the mostly positive correlations in SmO
data shown by the current research, it is possible
that limitations in the use of the device may exist
when applied to different individuals or environ-
mental conditions. Our participants were trained ath-
letes with very little adipose tissue. However, thicker
tissue may alter the scattering of light from the Moxy
and inhibit the return of light to the sensors. Accord-
ingly, previous research has indicated that the cut-off
for successful measurement with NIRS is a body
mass index of 32 (McCully, Landsberg, Suarez,
Hofmann, & Posner, 1997). Thus, the Moxy
cannot be recommended for use in such individuals
until reliability studies using individuals with higher
body fat percentages have been conducted. Further,
during prolonged exercise, skin blood flow increases
as the need for heat dissipation becomes greater. Pre-
viously, an increase in either skin blood flow
(+149 AU) or whole-body temperature (+0.8°C)
have been associated with a rise in tissue oxygenation
(r= 0.95) (Davis, Fadel, Cui, Thomas, & Crandall,
2006). In the current study, a rise in skin and total
body temperatures were limited because the exercise
was performed in an air-conditioned laboratory, with
constant cool air-flow to the skin of the participant via
a fan. However, it is acknowledged that in field-based
exercise, these factors could influence Moxy data.
Lastly, although this study was designed to measure
the reliability of the Moxy in a testretest situation,
it did not measure its validity compared to a standard
NIRS device. While we have shown that the Moxy
gives reliable results, future research could investigate
whether these results correlate with other devices.
In conclusion, the current study demonstrates that
the Moxy produces reliable measurements during
exercise of lowmoderate intensity and can be used
alongside VO
to gain a clearer idea of how the
amount of O
absorbed by the body relates to that
taken up by the muscles. However, at higher intensi-
ties, the reliability of the SmO
decreases, possibly due to greater movement artefacts
or tissue ischaemia. Based on these results, the Moxy
appears to have similar reliability to traditional NIRS
The authors would like to thank the cyclists who gave
up their time to participate in this study.
Disclosure statement
No potential conflict of interest was reported by the authors.
This work was supported by a Massey University Doctoral
Austin, K. G., Daigle, K. A., Patterson, P., Cowman, J., Chelland,
S., & Haymes, E. M. (2005). Reliability of near-infrared spec-
troscopy for determining muscle oxygen saturation during exer-
cise. Research Quarterly for Exercise and Sport,76, 440449.
Bassett, D. R., & Howley, E. T. (2000). Limiting factors for
maximum oxygen uptake and determinants of endurance per-
formance. Medicine and Science in Sports and Exercise,32,70
84. doi:10.1097/00005768-200001000-00012
Bhambhani, Y. N. (2004). Muscle oxygenation trends during
dynamic exercise measured by near infrared spectroscopy.
6E. M. Crum et al.
Canadian Journal of Applied Physiology,29, 504523. doi:10.
Born, D., Stöggl, T., Swarén, M., & Björklund, G. (2016).
Running in hilly terrain: NIRS is more accurate to monitor
intensity than heart rate. International Journal of Sports
Physiology and Performance, Advance online publication.
Cornachione, K., McLaren, J., & Heil, D. P. (2014). Use of a wire-
less NIRS monitor to track changes in muscle oxygenation for
laboratory-based Nordic skiing test proto-col. In E. Müller, J.
Kröll, S. Kröll, S. Lindiger, J. Pfusterschmeid, & T. Stöggl
(Eds.), Science and Skiing VI, (pp. 369376). Maidenhead:
Meyer & Meyer Sport (UK) Ltd.
Davis, S. L., Fadel, P. J., Cui, J., Thomas, G. D., & Crandall, C. G.
(2006). Skin blood flow influences near-infrared spectroscopy-
derived measurements of tissue oxygenation during heat stress.
Journal of Applied Physiology,100, 221224. doi:10.1152/
De Blasi, R. A., Cope, M., Elwell, C., Safoue, F. & Ferrari, M.
(1993). Noninvasive measurement of human forearm oxygen
consumption by near infrared spectroscopy. European Journal
of Applied Physiology and Occupational Physiology 67, 2025.
Fortiori Design LLC. (2015). Introduction to muscle oxygen monitor-
ing with Moxy. Retrieved from
Honig, C. R., Connett, R. J., & Gayeski, T. (1992). O
and its interaction with metabolism: A systems view of aerobic
capacity. Medicine and Science in Sports and Exercise,24,4753.
Europe PMC ID:1548995.
Jobsis, F. F. (1977). Noninvasive, infrared monitoring of cerebral
and myocardial oxygen sufficiency and circulatory parameters.
Science,198, 12641267. doi:10.1126/science.929199
Kodejska, J., Michailov, M. L., & Balas, J. (2015). Forearm
muscle oxygenation during sustained isometric contractions in
rock climbers. Acta Universitatis Carolinae: Kinanthropologica,
51,4855. doi:10.14712/23366052.2015.31
Mancini, D. M., Bolinger, L., Li, H., Kendrick, K., Chance, B., &
Wilson, J. R. (1994). Validation of near-infrared spectroscopy
in humans. Journal of Applied Physiology,77, 27402747.
PMID: 7896615.
McCully, K. K., & Hamaoka, T. (2000). Near-infrared spec-
troscopy: What can it tell us about oxygen saturation in skeletal
muscle? Exercise and Sport Sciences Reviews,28, 123127. PMID:
McCully, K. K., Landsberg, L., Suarez, M., Hofmann, M., &
Posner, J. D. (1997). Identification of peripheral vascular
disease in elderly subjects using optical spectroscopy. The
Journals of Gerontology Series A: Biological Sciences and Medical
Sciences,52A, B159B165. doi:10.1093/gerona/52A.3.B159
Overstreet, B., Bassett, D., Crouter, S., Rider, B., & Parr, B.
(2016). Portable open-circuit spirometry systems: A review.
The Journal of Sports Medicine and Physical Fitness,57, 227
237. doi:10.23736/S0022-4707.16.06049-7
Raasch, C. C., Zajac, F. E., Ma, B., & Levine, W. S. (1997).
Muscle coordination of maximum-speed pedaling. Journal
of Biomechanics,30, 595602. doi:10.1016/S0021-9290
Tew, G. A., Klonizakis, M., Moss, J., Ruddock, A. D., Saxton, A.
D., & Hodges, G. J. (2011). Reproducibility of cutaneous
thermal hyperaemia assessed by laser Doppler flowmetry in
young and older adults. Microvascular Research,81,177182.
Thiel, C., Vogt, L., Himmelreich, H., Hubscher, M., & Banzer, W.
(2011). Reproducibility of muscle oxygen saturation.
International Journal of Sports Medicine,32, 277280. doi:10.
Reliability of the Moxy oxygen monitor 7
... Fourteen trained, and recreationally trained cyclists (7 females & 7 males, 74.1 ± 10.5 kg, 32.1 ± 7.6 years of age, 170.0 ± 11.0 cm, 11.3 ± 5.4 mm VL skinfold thickness, and 55.0 ± 9.1 ml·kg·min −1 maximum oxygen uptake) volunteered and provided written informed consent to participate in the study (19). To obtain sufficient power of β = 0.8 with α = 0.05, an a priori sample size calculation was made in G*Power software (version, Kiel, Germany) using previously reported data from other groups that compared SmO 2 values within and between sessions during ramp incremental tests and severe intensity efforts (16,(20)(21)(22)(23). This study was approved by the research ethics committee of The University of British Columbia and was conducted in accordance with principles established in the Declaration of Helsinki, except for registration in a database. ...
... The Moxy sensor provides measures of total heme concentration (tHb + Mb in arbitrary units), and muscle O 2 saturation (SmO 2 as a percent). The SmO 2 signal was used as the primary output variable in this study (10,11,21). SmO 2 was measured every 2 s (0.5 Hz) and raw data were smoothed to 5second moving averages as per manufacturer default settings. ...
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Near-infrared spectroscopy (NIRS) quantifies muscle oxygenation (SmO2) during exercise. Muscle oxygenation response to self-paced, severe-intensity cycling remains unclear. Observing SmO2 can provide cycling professionals with the ability to assess muscular response, helping optimize decision-making. We aimed to describe the effect of self-paced severe intensity bouts on SmO2, measured noninvasively by a wearable NIRS sensor on the vastus lateralis (VL) muscle, and examine its reliability. We hypothesized a greater desaturation response with each bout, whereas, between trials, good reliability would be observed. Fourteen recreationally trained, and trained cyclists completed a ramp test to determine the power output (PO) at the respiratory compensation point (RCP). Athletes completed two subsequent visits of 50-minute sessions that included four severe-intensity bouts done at 5% above RCP PO. Muscle oxygenation in the VL was monitored using a wearable NIRS device. Measures included mean PO, heart-rate (HR), cadence, and SmO2 at bout onset, during work (work SmO2), and ΔSmO2. The bouts were compared using a one-way repeated measures ANOVA. For significant differences, a Fisher's least square difference post-hoc analysis was used. A two-way repeated measures ANOVA was used using trial and bout as main factors. Intraclass correlations (ICC) were used to quantify relative reliability for mean work, and standard error of the measurement (SEM) was used to quantify absolute agreement of mean work SmO2. Both PO and cadence showed no effect of bout or trial. Heart-rate at bout 2 (168 ± 8 bpm) and 4 (170 ± 7 bpm) were higher than bout 1 (160 ± 6 bpm). Onset SmO2 (%) response significantly increased in the final two bouts of the session. Mean work SmO2 increased across bouts, with the highest value displayed in bout 4 (36 ± 22%). ΔSmO2 showed a smaller desaturation response during bout 4 (27 ± 10%) compared to bout 3 (31 ± 10%). Mean work SmO2 ICC showed good reliability (ICC = 0.87), and SEM was 12% (CI 9-15%). We concluded that a non-invasive, affordable, wearable NIRS sensor demonstrated the heterogeneous muscle oxygenation response during severe intensity cycling bouts with good reliability in trained cyclists.
... One promising application, which seems feasible in climbing, is near-infrared spectroscopy (NIRS). NIRS is a non-invasive technique designed to monitor muscle oxygen saturation (SmO2) in vivo [10] and shows good results regarding validity and reliability [11]. This seems practical, as it provides insight into the fatigue of the muscles [12], is easy to attach, and is almost unnoticeable by the climber once they get used to it. ...
... Therefore, to improve accuracy and muscle coverage, future work should also consider other sensors e.g., the OctaMon M system (Artinis Medical Systems, Elst, Netherlands). Moreover, there are some limitations of NIRS sensors in general: [11] suggests that adipose tissues under the skin and the cutaneous blood flow when exercising could modify the results of the spectroscopy. The authors of reference [14] point out that the measurement is dependent on blood flow, oxygen consumption, and mitochondrial respiratory capacity. ...
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The objectification of acute fatigue (during isometric muscle contraction) and cumulative fatigue (due to multiple intermittent isometric muscle contractions) plays an important role in sport climbing. The data of 42 participants were used in the study. Climbing performance was operationalized using maximal climbing-specific holding time (CSHT) by performing dead hangs. The test started with an initial measurement of handgrip strength (HGS) followed by three intermittent measurements of CSHT and HGS. During the test, finger flexor muscle oxygen saturation (SmO2) was measured using a near-infrared spectroscopy wearable biosensor. Significant reductions in CSHT and HGS could be found (p < 0.001), which indicates that the consecutive maximal isometric holding introduces cumulative fatigue. The reduction in CSHT did not correlate with a reduction in HGS over multiple consecutive maximal dead hangs (p > 0.35). Furthermore, there were no significant differences in initial SmO2 level, SmO2 level at termination, SmO2 recovery, and mean negative slope of the SmO2 saturation reduction between the different measurements (p > 0.24). Significant differences were found between pre-, termination-, and recovery-(10 s after termination) SmO2 levels (p < 0.001). Therefore, monitoring acute fatigue using athletes' termination SmO2 saturation seems promising. By contrast, the measurement of HGS and muscle oxygen metabolism seems inappropriate for monitoring cumulative fatigue during intermittent isometric climbing-specific muscle contractions.
... The NIRS instrument used was a Moxy Muscle Oxygen Monitor (Moxy Monitor, Minnesota, USA). This device [27][28][29][30][31] uses near-infrared light emitted from the light transmitter of a probe attached to the skin on the surface of the target muscle. Near-infrared light is detected by the light receiver after being absorbed and scattered as it passes through the skin, subcutaneous fat, and muscle. ...
... ((oxidized hemoglobin + oxidized myoglobin)/(total amount of hemoglobin + myoglobin)) × 100% SmO 2 is used as an index that reflects the dynamic balance between oxygen supplied in the circulation by microvessels and oxygen consumption by the muscles [28][29][30][31][32]. SmO 2 measurements have been made during various walking tasks in previous studies, and this method is also used to evaluate the dynamic contraction of muscles during walking [33][34][35]. ...
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The response of muscle oxygen saturation, which is an index for the energy metabolism of muscles during walking in children, and its relationship to the physiological cost index, which indicates walking efficiency, are unknown. This study aimed to evaluate muscle oxygen saturation in lower extremity muscles during walking in children, its changes with age, and the relationship between the physiological cost index. The oxygen saturation was measured by the amount of change during a two-minute walk, and the physiological cost index was calculated from the change in heart rate before and after exercise and walking speed. Results were compared for each muscle, and the correlation between the two was examined. Changes in muscle oxygen saturation were greater in the lower leg muscles, significantly greater in the tibialis anterior at six to seven years, and in the gastrocnemius medial head at eight to ten years. The physiological cost index was significantly correlated with changes in muscle oxygen saturation in the tibialis anterior (r = 0.44, p < 0.001). The lower leg muscles were metabolically active in children's gait, and their response varied with age. Moreover, the muscle oxygenation dynamics of the tibialis anterior may influence walking efficiency.
... Hemoglobin oxygen saturation was measured using 2 Moxy Monitors (Fortiori Design LLC, Hutchinson, MN), as published. 28 The monitors were placed on the belly of the medial gastrocnemius and secured with cover-roll tape strips. Each monitor was connected to a Samsung Galaxy Tablet (Samsung, Seoul, South Korea) for live data tracking throughout the study. ...
Background: Peripheral arterial disease (PAD) causes leg muscle damage due to inadequate perfusion and increases cardiovascular (CV) events and mortality 2-3 fold. It is unclear if PAD is a biomarker for high-risk cardiovascular disease or if skeletal muscle injury harms arterial health. The objective of this work is to test if serum myoglobin levels (myoglobinemia) is a marker of PAD, and if so, whether myoglobin impairs vascular health. Study design: Patient blood samples were collected from PAD and control (no PAD) patients and interrogated for myoglobin concentrations and nitric oxide (NO) bioavailability. Patient mortality over time was captured from the medical record. Myoglobin activity was tested on endothelial cells and arterial function. Results: Myoglobin is a biomarker for symptomatic PAD and was inversely related to NO bioavailability. 200 ng/mL of myoglobin in vitro increased EC permeability in vitro and decreased nitrate bioavailability. Ex vivo, 100 ng/mL myoglobin increased vascular tone in naïve murine aortas ~1.5x, impairing absolute vessel relaxation. In vivo, we demonstrated that myoglobinemia caused impaired flow-mediated dilation in a porcine model. Patients presenting with myoglobin levels of 100 ng/mL or greater had significantly more deaths than those with less than 100 ng/mL. Conclusions: Using a combination of patient data, in vitro, ex vivo, and in vivo testing, we found that myoglobin is a biomarker for symptomatic PAD and a potent regulator of arterial health that can increase vascular tone, vascular permeability, and cause endothelial dysfunction. All of which may contribute to the vulnerability of PAD patients to CV events and death.
... This device is reliable at low and moderate intensity for measuring consumption of muscle oxygen (SmO2; ICC: r = 0.773-0.992) [34]. The device was placed in the vast lateral quadriceps between the greater trochanter and the lateral femoral epicondyle. ...
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Previous studies have reported that people with fibromyalgia (FM) could suffer from mitochondrial dysfunction. However, the consumption of muscle oxygen during physical exercise has been poorly studied. Therefore, this study aimed to explore the response of muscle oxygen during a fatigue protocol in people with FM and healthy controls (HC). In addition, the peak torque and the total work were assessed. A total of 31 participants (eighteen were people with fibromyalgia and thirteen were healthy controls) were enrolled in this cross-sectional study. All the participants underwent a fatigue protocol consisting of 20 repetitions at 180°·s−1 of quadriceps flexions and extensions using a Biodex System 3. The muscle oxygen saturation (SmO2), total hemoglobin (THb), deoxygenated hemoglobin (HHb) and oxygenated hemoglobin (O2Hb) values were measured using a portable near-infrared spectroscopy (NIRS) device. Significant differences between people with FM and healthy controls were found at baseline: SmO2 (FM: 56.03 ± 21.36; HC: 77.41 ± 10.82; p = 0.036), O2Hb (FM: 6.69 ± 2.59; HC: 9.37 ± 1.31; p = 0.030) and HHb (FM: 5.20 ± 2.51; HC: 2.73 ± 1.32; p = 0.039); during the fatigue protocol: SmO2 (FM: 48.54 ± 19.96; HC: 58.87 ± 19.72; p = 0.038), O2Hb (FM: 5.70 ± 2.34; HC: 7.06 ± 2.09; p = 0.027) and HHb (FM: 5.69 ± 2.65; HC: 4.81 ± 2.39; p = 0.048); and in the recovery at three min and six min for SmO2, O2Hb and HHb (p < 0.005). Furthermore, healthy control values of SmO2, O2Hb and HHb have been significantly altered by the fatigue protocol (p < 0.005). In contrast, people with FM did not show any significant alteration in these values. Moreover, significant differences were found in the peak torque at extension (FM: 62.48 ± 24.45; HC: 88.31 ± 23.51; p = 0.033) and flexion (FM: 24.16 ± 11.58; HC: 42.05 ± 9.85; p = 0.010), and the total work performed at leg extension (FM: 1039.78 ± 434.51; HC: 1535.61 ± 474.22; p = 0.007) and flexion (FM: 423.79 ± 239.89; HC: 797.16 ± 194.37; p = 0.005).
... These devices are non-invasive low-cost and functional instruments that make it possible for us to know the behavior of muscle oximetry and its derivatives in real-time through Bluetooth technology [28]. In addition, they have proven to be valid and reliable [7], [9], [10], [23], [28], [36]. Technically, NIRS illuminates skeletal muscle with light in the near-infrared spectrum and detects the light reflected through it. ...
Purpose: The objective of the study was to describe and compare the acute response of muscle oxygen saturation (SmO2) and hemoglobin concentration (Hgb) in the vastus lateralis (VL) during resistance exercise protocols until failure. Methods: Sixteen males were considered (mean ± SD, age = 36.12 ± 6.40 years). Two familiarization sessions and one evaluation session were carried out where three force protocols were executed in the VL, one of them was isometric load (P1) and two of dynamic load (P2 and P3). SmO2 [%] and Hgb [g/dL] were measured before and after each of these protocols. For P1, three series of 8 s of maximum isometric strength with the rest of 60 s between each set, the average isometric strength (AIS), and the isometric peak strength (IPS) were also recorded. After five minutes, P2 was performed, with an initial load of 40% of AIS. Then, at 30 minutes, P3 was performed considering an initial load of 40% of IPS. Results: The results suggest (I) minimum levels of SmO2 (66.31 ± 9.38%) and Hgb (12.22 ± 0.55 g/dL) during P2, (II) no significant differences were observed between the average loads of the respective protocols for SmO2 and (III) muscle Hgb differed significantly between rest with P1 and P3. Conclusions: Exercises of increasing intensity and of short duration do not significantly modify SmO2. However, Hgb increases substantially compared baseline values.
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Duathlon is a rapidly promoting sport, so it is necessary to identify the factors that influence performance. This study aimed to analyse internal and external loads and the interactions between them during running legs before and after cycling in duathlon. Twenty-three male and female athletes participated in a simulated duath-lon (5k-20k-5k). Internal workload was assessed using the rate of perceived exertion (RPE) and heart rate (maximum: HRMAX; average: HRAVG; R-R interval), whereas external workload was assessed using inertial sensors (Player Load by RealTrack, PLRT) attached to six body locations. The results showed that both running legs presented an increasing trend in RPE, HRMAX, and HRAVG throughout the kilometres, while the R-R interval decreased. The PLRT of the upper and lower back, knee, and ankle increased throughout the first running leg but not in the second. The PLRT was greater in the lower body than in the upper body because of energy absorption. RPE was higher in the second running leg than in the first leg. In conclusion, the cycling leg affects the internal and external load between running legs in duathlon. Load monitoring can help coaches understand duathletes' performance and design specific training strategies to reduce fatigue during competition. ARTICLE HISTORY
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El modelo de oxigenación critica (OC) representa “la mayor tasa metabólica resultante del suministro de energía a través de la fosforilación oxidativa y que a nivel de sustrato alcanza un estado estable” (Feldmann & Erlacher, 2021). El nivel de OC podría influir sobre la aparición de la fatiga en esfuerzos de alta intensidad. El objetivo del estudio fue evaluar la OC durante una prueba de sprint-repetidos antes y después de una pretemporada para relacionarlo con otros parámetros de rendimiento físico. 16 futbolistas semiprofesionales realizaron un test de sprint-repetidos (RSA) con 8 sprints x 20s recuperación. Se midió el tiempo y velocidad con fotocélulas infrarrojas de las cuales se obtuvieron las variables metabólicas: el gasto energético (CE) y la potencia metabólica (PM) (Osgnach et al., 2010). También se midieron la frecuencia Cardiaca y la saturación de oxigeno muscular (Moxy, Minnesota, USA), así como la composición corporal (CC) y la potencia de salto en CMJ. La OC fue observada por un experto utilizando el modelo de Feldmann & Erlacher (2021) y fue descrita como la respuesta interindividual (MDC) de la extracción de oxígeno (∇%SmO2) obtenida de las tasas de desaturación y resaturación durante la RSA (Vasquez-Bonilla et al., 2021). Después de la pretemporada, el 81% de los participantes mostraron una tendencia de mejora en la CO y la tolerancia al ejercicio en el RSA (MDC: 6,6% p= 0.00). Asimismo, la mejora de la velocidad, EC, PM y CC estuvo asociada con la OC. La OC del musculo puede identificar adaptaciones al entrenamiento y, por lo tanto, puede ser considerado un factor de rendimiento físico en futbolistas.
Summary Objectives: Muscle oxygenation capacity is a metabolic component that can influence the bilateral strength asymmetry. This study measured the muscle oxygen saturation (SmO2) during a protocol of high-intensity isokinetic fatigue (FAT) and its relationship with the body composition (BD) at the local level of the vastus lateralis. Methods: Twenty-two rugby players (age 22.5 ± 4.6 years, weight 89.8 ± 12.6 kg, height 176.4 ± 7.8 cm) performed a FAT test to obtain the peak moments (PM) torque of the knee muscle flexors and extensors. SmO2 dynamics was evaluated using a portable NIRS, where muscle oxygen consumption, critical oxygenation, muscle oxygen extraction and recovery curves were obtained. The localized thigh BD was evaluated with dual-energy absorptiometry (DEXA). The tests were evaluated by dominant leg (DL) and non-dominant leg (not DL). Results: Greater average peak torque were found in the DL of the knee extensor muscles (DL: 157 ± 28 vs. NDL: 148 ± 25; P = 0.028). Similarly, a SmO2 difference (DL: 11.7 ± 10.1 vs. NDL: 16.3 ± 13.2; P = 0.044) and critical oxygenation (DL: 20.8 ± 10.1 vs. NDL: 26.3 ± 12; P = 0.049) is associated with greater bilateral strength asymmetry (r = 0.618 P = 0.01 and r = 0.447 P = 0.03). Also, a greater muscle mass showed an association with a better muscle oxygen extraction.Conclusions: This study highlights the use of SmO2 dynamics as a complement to isokinetic tests in order to identify muscle metabolism and muscle imbalances in team sports such as rugby.
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Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain and associated fatigue, sleep disturbances, and other cognitive and somatic symptoms. A multidisciplinary approach including pharmacological therapies along with behavioral therapy, exercise, patient education, and pain management is a possible solution for the treatment of this disease. The EXOPULSE Mollii® method (EXONEURAL NETWORK AB, Danderyd, Sweden) is an innovative approach for non-invasive and self-administered electrical stimulation with multiple electrodes incorporated in a full-body suit, with already proven benefits for other diseases. Therefore, the present case report study aims to evaluate the effects that a 60 min session with the EXOPULSE Mollii suit has on a female fibromyalgia patient. After the intervention, we can conclude that a 60 min session with the EXOPULSE Mollii suit has beneficial effects on pain perception, muscle oxygenation, parasympathetic modulation, and function in a female fibromyalgia patient.
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Purpose: To 1) investigate the cardiorespiratory and metabolic response of trail running and 2) evaluate whether heart rate (HR) adequately reflects the exercise intensity or whether the tissue saturation index (TSI) could provide a more accurate measure when running in hilly terrain. Methods: Seventeen competitive runners (female: n=4, V'O2max: 55±6 mL·kg-1·min-1; male: n=13, V'O2max: 68±6 mL·kg-1·min-1) performed a time trial on an off-road trail course. The course was made up of two laps covering a total distance of 7 km and included six steep up- and downhill sections with an elevation gain of 486 m. All runners were equipped with a portable breath-by-breath gas analyzer, HR belt, global positioning system receiver and near-infrared spectroscopy (NIRS) device to measure the TSI. Results: During the trail run, the exercise intensity within the uphill and downhill sections was 94±2% and 91±3% of HRmax, 84±8% and 68±7% of V'O2max, respectively. The oxygen uptake (V'O2) increased within the uphill and decreased within the downhill sections (P< .01). While HR was unaffected by the altering slope conditions, the TSI was inversely correlated to the changes in V'O2 (r = - .70, P< .05). Conclusions: The HR was unaffected by the continuously changing exercise intensity, however, the TSI reflected the alternations in V'O2. Recently used exclusively for scientific purpose, this NIRS based variable may offer a more accurate alternative to HR to monitor running intensity in the future, especially for training and competition in hilly terrain.
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Background. Bouldering and lead climbing are divergent disciplines of the sport of rock climbing. Bouldering moves are short and powerful, whilst sport climbing is longer and require a greater degree of endurance. Aim. The aim of this study was to compare forearm muscle oxygenation during sustained isometric contraction between lead climbers (LC) and boulderers (BO). Methods. Eight BO and twelve LC completed maximal finger flexor strength test and sustained contractions to exhaustion at 60% of maximum voluntary contraction (MVC). Differences between BO and LC in maximal strength, time to exhaustion, force time integral (FTI), and tissue oxygenation (SmO 2) were assessed by t-test for independent samples. Results. LC showed significantly lower level of average tissue oxygenation (BO 38.9% SmO 2 , s = 7.4; LC 28.7% SmO 2 , s = 7.1) and maximal tissue deoxygenation (BO 25.6% SmO 2 , s = 8.2; LC 13.5% SmO 2 , s = 8.5). LC demonstrated significantly lower finger flexor strength (519 N, s = 72) than BO (621 N, s = 142). LC sustained a longer time of contraction (not significantly) (BO 52.2 s, s = 11.5; LC 60.6 s, s = 13) and achieved a similar value of FTI (BO 17421 Ns, s = 4291; LO 17476 Ns, s = 5036) in the endurance test. Conclusions. The results showed lower deoxygenation during sustained contraction in BO than LC despite similar FTI, indicating different local metabolic pathways in both groups.
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The present study evaluated the reproducibility of tissue oxygenation in relation to oxygen consumption (VO2) across cycle exercise intensities in a test-retest design. 12 subjects (25.7±2.1 years; 24.7±1.9 kg · m(-2)) twice performed an incremental bicycle exercise protocol, while tissue oxygen saturation (StO2) in the vastus lateralis muscle was monitored by a commercially available NIRS unit and VO2 determined by an open-circuit indirect calorimetric system. Coefficients of variation across rest, workloads corresponding to 25, 50 and 75% of individual maximum capacity, and maximum load were 5.8, 4.6, 6.1, 8.0, 11.0% (StO2) and 7.6, 6.0, 3.7, 3.4, 3.1% (VO2), respectively. 95 % CI of relative test-retest differences ranged from -5.6 to +5.4% at 25% load to -17.2 to +7.5% at maximum load for StO2 and from -7.3 to +7.7% at rest to -3.3 to +3.2% at maximum load for VO2. With advancing exercise intensity, within-subject variability of StO2 was augmented, whereas VO2 variability slightly attenuated. NIRS measurements at higher workloads need to be interpreted with caution.
Aim: The purpose of this review is to describe the evolution of portable open-circuit spirometry systems, and discuss their validity, reliability, and principles of operation. Methods: Eleven devices were selected for review: the Oxylog, Aerosport KB1-C, Cosmed K2, Cosmed K4RQ, Cosmed K4b2, MetaMax I, MetaMax II, Metamax3B/VmaxST, Medgraphics VO2000, Oxycon Mobile I and Oxycon Mobile II. The validity (compared to the Douglas bag method (DBM)) and reliability of each device for measuring VO2 was summarized. Results: Mean differences in resting measurements of VO2 were within ±0.05 L∙min-1 for all devices except one (difference of 0.17 L∙min-1). When compared to the DBM, VO2 differences for all devices ranged from 0.01 L∙min-1 to 0.29 L∙min-1 during submaximal intensity exercise and from 0.01 L∙min-1 to 0.36 L∙min-1 during vigorous/maximal intensity. During submaximal and maximal intensities, ICC ranged from 0.66-0.99 and CV ranged from 2.0-14.2%. Of these devices, four used breath-by-breath technology and six used micro-proportional sampling technology. Validity and reliability of devices did not seem to differ between methods of gas collection. Conclusion: Of the three commercially available devices in 2015, all were found to be reliable. Two of the three systems (Cosmed K4b2 and Oxycon Mobile II) provided valid estimates of VO2 (mean values within ±0.10 L/min-1 of DBM) during rest, and submaximal and maximal intensities, while the MetaMax3B slightly overestimated VO2, particularly at maximal exercise.
The relatively good transparency of biological materials in the near infrared region of the spectrum permits sufficient photon transmission through organs in situ for the monitoring of cellular events. Observations by infrared transillumination in the exposed heart and in the brain in cephalo without surgical intervention show that oxygen sufficiency for cytochrome a,a3, function, changes in tissue blood volume, and the average hemoglobin-oxyhemoglobin equilibrium can be recorded effectively and in continuous fashion for research and clinical purposes. The copper atom associated with heme a3 did not respond to anoxia and may be reduced under normoxic conditions, whereas the heme-a copper was at least partially reducible.
The primary objective of this study was to assess the inter-day reproducibility of cutaneous thermal hyperaemia, as assessed using integrating-probe laser Doppler flowmetry (LDF), in young and older men. A secondary objective was to identify the most reproducible form of data expression. Cutaneous thermal hyperaemia was assessed on the forearm in 14 young (25±1 year) and 14 older (65±1 year) men, using integrating-probe LDF. The test was repeated 7-14 days later. The baseline, initial peak, and plateau phases of the data traces were identified and expressed as raw cutaneous vascular conductance (CVC), CVC normalised to baseline (%CVC(BL)), and CVC normalised to 44°C vasodilatation (%CVC(MAX)). Reproducibility was assessed using the coefficient of variation (CV) and intraclass correlation coefficient (ICC) statistics. The inter-day reproducibility was dependent on how the data were expressed. The reproducibility of the initial peak and plateau was equally acceptable in both young and older adults when data were expressed as %CVC(MAX) (e.g., CVs ranging from 4 to 11%). However, the baseline phase was poorly reproducible in both groups irrespective of the data presentation method used (e.g., CVs ranging from 25 to 35%). Furthermore, expressing data as raw CVC or as %CVC(BL) generally showed poor reproducibility for both groups and all phases of the test (e.g., CVs ranging from 15 to 39%). Integrating-probe LDF is a reproducible technique to assess cutaneous thermal hyperaemia on the forearm when data are expressed as %CVC(MAX) in healthy young and older adults without history of hypertension or taking system drugs.
This commentary demonstrates that VO2max depends, in part, on diffusive O2 transport; exercise hyperemia is necessary but not sufficient. Experiments and new mathematical models place the principal site of resistance to O2 diffusion between the surface of a red cell and the sarcolemma. The large drop in PO2 over this short distance is caused by high flux density and absence of heme protein O2 carrier in this region. PO2 gradients within red myocytes are shallow at high VO2 because myoglobin acts as O2 carrier and PO2 buffer. At high VO2 cell PO2 is less than 5 torr, the myoglobin P50. Low cell PO2 relative to blood PO2 is essential to a) maintain the driving force on diffusion as capillary PO2 falls, and b) to increase myoglobin-facilitated diffusion and the overall O2 conductance. O2 per se does not limit mitochondrial ATP production under normal circumstances because the low O2 drive on electron transport is compensated by greater phosphorylation and redox drives. These metabolic adaptations support transcapillary diffusion by defending VO2 at the low cell PO2 required to extract O2 from blood. Thus aerobic capacity is a distributed property, dependent on the interaction of transport and metabolism as a system.
Near-infrared (NIR) spectroscopy is a noninvasive technique that uses the differential absorption properties of hemoglobin to evaluate skeletal muscle oxygenation. Oxygenated and deoxygenated hemoglobin absorb light equally at 800 nm, whereas at 760 nm absorption is primarily from deoxygenated hemoglobin. Therefore, monitoring these two wavelengths provides an index of deoxygenation. To investigate whether venous oxygen saturation and absorption between 760 and 800 nm (760-800 nm absorption) are correlated, both were measured during forearm exercise. Significant correlations were observed in all subjects (r = 0.92 +/- 0.07; P < 0.05). The contribution of skin flow to the changes in 760-800 nm absorption was investigated by simultaneous measurement of skin flow by laser flow Doppler and NIR recordings during hot water immersion. Changes in skin flow but not 760-800 nm absorption were noted. Intra-arterial infusions of nitroprusside and norepinephrine were performed to study the effect of alteration of muscle perfusion on 760-800 nm absorption. Limb flow was measured with venous plethysmography. Percent oxygenation increased with nitroprusside and decreased with norepinephrine. Finally, the contribution of myoglobin to the 760-800 nm absorption was assessed by using 1H-magnetic resonance spectroscopy. At peak exercise, percent NIR deoxygenation during exercise was 80 +/- 7%, but only one subject exhibited a small deoxygenated myoglobin signal. In conclusion, 760-800 nm absorption is 1) closely correlated with venous oxygen saturation, 2) minimally affected by skin blood flow, 3) altered by changes in limb perfusion, and 4) primarily derived from deoxygenated hemoglobin and not myoglobin.
This study reported on the application of near infrared spectroscopy (NIRS) to noninvasive measurements of forearm brachio-radial muscle oxygen consumption (VO2) and recovery time (tr) in untrained volunteers. Seven healthy subjects were submitted to four consecutive protocols involving measurements made at rest, the induction of an ischaemia, and during a maximal increase of metabolic demand achieved with and without vascular occlusion. Two isometric maximal voluntary contractions (MVC) of 30-s duration were executed with and without vascular occlusion and a 50% MVC lasting 125 s was also performed. The protocols were repeated on 2 different days. The results showed that, during vascular occlusion at rest, the time to 95% of the final haemoglobin (Hb) + myoglobin (Mb) desaturation value was independent of VO2. The MVC, performed during vascular occlusion, caused complete Hb+Mb desaturation in 15-20 s, which was not followed by any further desaturation when the second contraction was performed. No difference was found between VO2 during MVC with and without vascular occlusion. A consistent difference was seen between VO2 measured during occlusion at rest and VO2 measured during MVC with and without occlusion. During prolonged exercise (125 s) Hb+Mb desaturation was maintained for the whole contraction period. The results of this study show that VO2 can be measured noninvasively by NIRS. The VO2 during MVC was very similar both in the presence and absence of blood flow limitation in most of the subjects tested. This would suggest that muscle VO2 might be accurately evaluated dynamically without cuff occlusion.