Performance and physiological consequences of roll dynamics during cross-country mountain bike racing : a thesis presented in partial fulfilment of the requirements for the Doctor of Philosophy via publication in Sport & Exercise Science, Massey University, Manawatu Campus, New Zealand
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Date
2015
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
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The Author
Abstract
Background:
Understanding
the
interaction
between
physical
work
done
and
subsequent
physiological
responses
is
key
to
the
prescription
of
optimal
training.
Olympic
format
cross-‐
country
mountain
bike
racing
presents
unique
challenges
with
regards
to
understanding
the
relationship
between
propulsive
and
non-‐propulsive
work,
the
interaction
with
performance,
and
associated
physiological
responses.
Aims:
The
aims
of
this
thesis
were
to:
1)
Determine
the
nature
of
work
demand
during
simulated
cross-‐country
mountain
bike
racing;
2)
Quantify
vibration
exposure
during
cross-‐
country
mountain
biking
and
the
interaction
of
bike-‐body
in
the
subsequent
energy
dissipation;
3)
Establish
additional
work
done
and
physiological
responses
to
riding
on
surface-‐terrain
variations;
4)
Investigate
technological
interventions
designed
to
reduce
vibration
exposure
during
cross-‐country
mountain
biking
and
the
interaction
with
performance
and
cycling
economy.
Methods
&
Results:
To
address
these
aims
four
original
experimental
investigations
involving
two
descriptive
elements
and
four
experimental
interventions
were
conducted.
Study
1:
Participants
(n=7)
completed
a
submaximal
treadmill
test
on
bicycles
in
order
to
establish
the
power:oxygen
uptake
relationship,
which
when
combined
with
an
ergometer
maximal
ramp
test,
enabled
the
prediction
of
oxygen
demand
during
the
field
and
thus
estimations
of
aerobic
and
anaerobic
contributions
to
work
done.
Field
work
involved
particpants
riding
at
race
pace
on
a
cross-‐country
mountain
bike
course
whilst
cadence,
power
output,
oxygen
consumption,
heart
rate,
speed
and
geographical
position
were
recorded.
The
data
show
power
output
and
cadence
to
be
highly
variable
with
one
power
surge
every
32
s
and
a
supramaximal
effort
(greater
than
power
associated
with
VO2
max)
every
106
s.
The
majority
of
time
(20.7
±
8.3
%)
was
spent
pedalling
at
a
low
velocity-‐high
force,
whilst
physiological variables
%
VO2
max
(77
±
5
%)
and
%
HRmax
(93
±
2
%)
were
consistantly
elevated
to
a
high
level
throughout
the
lap.
Importantly,
the
results
identified
that
terrain
significantly
affecteded
power
output
(70.9
7.5
vs
41.0
±
9.2
%
Wmax);
%
VO2
max
(80
±
2
vs
72
±
4
%)
but
not
%
HRmax
(94
±
2
vs
91
±
1
%)
for
uphill
and
downhill,
respectively.
Accordingly,
it
was
hypothesised
that
there
was
an
additional
non-‐propulsive
physical
stress
during
downhill
riding,
affording
less
recovery
compared
to
road
cycling.
Study
2:
Participant
(n=8)
completed
one
lap
of
a
cross-‐country
track
at
race
pace
under
two
conditions
(26”
vs
29”
wheels)
whilst
tri-‐axial
accelerometers
located
on
the
bicycle
(handlebar
and
seatpost)
and
the
rider
(wrist,
ankle,
lower
back,
and
forehead)
recorded
accelerations
(128
Hz)
to
quantify
vibrations
over
the
whole
lap
and
for
terrain
specific
sections
(uphill
vs
downhill).
The
result
showed
that
significant
vibration
attenuation
occurred
from
locations
at
the
bike
and
bike-‐body
interface
compared
to
the
lower
back
and
forehead.
The
reduction
of
accelerations
at
the
lower
back
and
forehead
implies
additional
non-‐propulsive,
muscular
challenges
which
may
limit
recovery
during
periods
of
non-‐propulsive
load.
The
hypothesis
that
29”
wheels
would
reduce
vibration
exposure
was
inconclusive
as
29”
wheels
proved
to
be
significantly
quicker
(p=0.0020)
compared
to
26”
wheels
even
though
no
difference
was
found
between
power
output
(p=0.3062)
and
heart
rate
(p=0.8423).
As
such
the
greater
velocity
incurred
by
29”
wheels
may
have
caused
the
greater
vibration
exposure
seen
in
the
29”
wheels.
Study
3:
Participants
(n=7)
ascended
a
tar-‐sealed
road
climb
and
a
singletrack
off-‐road
climb
of
identical
length
and
gradient
at
the
same
speed.
Tri-‐axial
accelerometers
(128
Hz)
located
at
the
handlebar,
wrist,
ankle,
seat
post,
lower
back,
and
forehead
were
used
to
quantify
vibration
exposure
while
power
output
,
cadence,
heart
rate
and
oxygen
consumption
were
used
todetermine
work
done
and
physiological
cost.
Accelerations
signified
(P<0.0001)
greater
vibration
exposure
for
off-‐road
compared
to
tar-‐sealed
riding
and
post-‐hoc
analysis
identified
differences
at
the
bike
and
bike-‐body
interface
but
not
the
lower
back
and
forehead.
This
indicates
a
greater
non-‐propulsive
component
in
the
form
of
vibration
damping
to
off-‐road
cycling
compared
to
road
cycling,
reflected
by
significant
increases
in
work
done
(280
±
69
vs
312
±
74
W;
p=0.0003).
This
was
associated
with
a
greater
rate
of
oxygen
consumption
(48.5
±
7.5
vs
51.4
±
7.3
ml⋅kg-‐1⋅min-‐1;
p=0.0033)
and
a
higher
heart
rate
(161
±
10
vs
170
±
10
bpm;
p=0.0001)
for
tar-‐sealed
road
and
off-‐road
conditions,
respectively.
These
findings
advocate
that
technological
interventions
aimed
at
decreasing
vibration
exposure
could
increase
cycling
economy
and
therefore
improve
performance.
Study
4:
Participants
(n=8)
completed
a
lap
of
a
cross-‐country
mountain
bike
circuit
under
two
conditions
(hardtail
and
full
suspension)
incorporating
the
same
downhill
section
twice
and
separated
by
a
forestry
road
climb.
The
particpants
were
asked
to
complete
the
downhill
sections
at
race
pace
while
the
climb
was
performed
at
a
power
output
associated
with
respiratory
compensation
point.
The
aim
of
this
was
to
control
physiological
variables
at
the
start
of
the
second
downhill.
Tri-‐axial
accelerometers
(located
at
the
handlebar,
wrist,
ankle,
seat
post,
lower
back,
and
forehead)
were
used
to
quantify
vibration
exposure
while
simultaneous
power
output
,
cadence,
heart
rate
and
oxygen
consumption
measurements
enabled
assessment
of
work
done
and
physiological
response.
Performance
was
determined
by
time
to
complete
the
overall
lap
and
specific
sections.
Physiological
demand
of
loaded
downhill
riding
(2nd
descent)
was
greater
than
unloaded
(1st
descent)
(p<0.0001).
Full
suspension
decreased
total
vibration
exposure
(p<0.01)
but
had
no
effect
on
performance
times
(p=0.9697)
or
power
outputs
(p=0.8600)
whilst
post-‐hoc
analysis
identified
trial
differences
(downhill
1
vs
downhill
2)
in
power
output
(p<0.0001)
but
not
for
time
(p>0.05).
Interestingly,
the
reduction
of
non-‐propulsive
work
did
not
affect
oxygen
consumption
(p=0.9840),
heart
rate
(p=0.9779
)
or
cycling
economy
(p=0.9240).
Conclusions:
This
thesis
demonstrates
that
surface-‐terrain
negatively
affectss
cycling
economy,
presenting
greater
physiological
responses
as
a
consequence
of
increased
non-‐propulsive
work.
This
is
likely
due
to
vibration
damping
throughout
the
soft
tissue
of
the
limbs
in
order
to
protect
the
central
nervous
system.
Reductions
in
vibration
exposure
diminished
work
done
and
physiological
response
for
surface
controlled
interventions,
yet
mechanical
system
modifications
capable
of
reducing
exposure
were
unable
to
alter
physiological
response
to
work
done.
Description
Keywords
All terrain cycling, Bicycle racing, Sports