Functional significance of extent and timing of muscle activation during double poling on-snow with increasing speed

Abstract

Purpose:
To evaluate the level of activation and timing of upper- and lower-body muscles during double poling at different speeds on snow.

Methods:
Nineteen well-trained cross-country skiers volunteered to double pole on a flat snowy track at different speeds (15, 18, 21 km h(-1)). The target speeds could be maintained by the skiers thanks to the use of an audio-pace system in combination with cones spaced equally alongside the track. Only 11 subjects were finally included in the analysis, since their actual speeds, calculated through a photocell system, were within ±0.5 km h(-1) from those requested. Cycle and poling durations were measured from the recordings of an accelerometer attached to a wrist, while the pattern and the level of muscle activation were evaluated from electromyographyc signals.

Results:
Double poling speed did not alter the sequence of muscle activation that started with hip flexors, continued with trunk flexors, shoulder, elbow and trunk extensors and ended with ankle plantar-flexors. However, higher speeds required an increasing involvement of thigh, trunk and shoulder muscles (P < 0.05) as well as an anticipation of their activation before pole plant (P < 0.05).

Conclusions:
A progressively earlier activation of trunk and lower limb muscles is a coordinative strategy that allows rapid achievement of optimal body posture prior to the exertion of poling phase. Moreover, earlier activation of these muscles as the speed increases provides adequate muscle stiffness in the shoulder and core regions for the acceptance of the poling load.

Full text

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Eur J Appl Physiol (2017) 117:2149–2157
DOI 10.1007/s00421-017-3703-0
ORIGINAL ARTICLE
Functional significance ofextent andtiming ofmuscle activation
duringdouble poling on‑snow withincreasing speed
ChiaraZoppirolli1,2· GennaroBoccia1,2,3· LorenzoBortolan1,2· FedericoSchena1,2·
BarbaraPellegrini1,2
Received: 2 March 2017 / Accepted: 11 August 2017 / Published online: 24 August 2017
© Springer-Verlag GmbH Germany 2017
Conclusions A progressively earlier activation of trunk and
lower limb muscles is a coordinative strategy that allows
rapid achievement of optimal body posture prior to the exer-
tion of poling phase. Moreover, earlier activation of these
muscles as the speed increases provides adequate muscle
stiffness in the shoulder and core regions for the acceptance
of the poling load.
Keywords On-snow skiing· Muscle sequence· Muscle
activation· Movement control
Abbreviations
Ag Silver
CT Cycle time
End End of the poling phase
EMG Electromyographyc
ESp Erector spinae muscle
GB Gigabyte
GMe Gastrocnemius medials muscle
iEMGratio Integral of EMG envelopes (expressed as
a ratio of the value measured during the
15kmh−1 trial)
LDo Latissimus dorsi muscle
MANOVA Multivariate analysis of variance
On Beginning of muscle activation
Off End of muscle activation
P P value
pk Peak of muscle activation
pkratio Amplitude of peak muscle activation
(expressed as a ratio of the value measured
during the 15kmh−1 trial)
PT Poling time
RAb Rectus abdominis muscle
RFe Rectus femoris muscle
RT Recovery time
Abstract
Purpose To evaluate the level of activation and timing of
upper- and lower-body muscles during double poling at dif-
ferent speeds on snow.
Methods Nineteen well-trained cross-country skiers volun-
teered to double pole on a flat snowy track at different speeds
(15, 18, 21kmh−1). The target speeds could be maintained
by the skiers thanks to the use of an audio-pace system in
combination with cones spaced equally alongside the track.
Only 11 subjects were finally included in the analysis, since
their actual speeds, calculated through a photocell system,
were within ±0.5kmh−1 from those requested. Cycle and
poling durations were measured from the recordings of an
accelerometer attached to a wrist, while the pattern and the
level of muscle activation were evaluated from electromyo-
graphyc signals.
Results Double poling speed did not alter the sequence
of muscle activation that started with hip flexors, contin-
ued with trunk flexors, shoulder, elbow and trunk exten-
sors and ended with ankle plantar-flexors. However, higher
speeds required an increasing involvement of thigh, trunk
and shoulder muscles (P<0.05) as well as an anticipation
of their activation before pole plant (P<0.05).
Communicated by Jean-René Lacour.
* Chiara Zoppirolli
chiara.zoppirolli@univr.it
1 CeRiSM (Research Center Sport Mountain & Health), Via
Matteo del Ben 5/b, 38068Rovereto, Italy
2 Neuroscience, Biomedicine andMovement Science
Department, University ofVerona, Verona, Italy
3 NeuroMuscularFunction Research Group, Department
ofMedical Sciences, School ofExercise andSport Sciences,
University ofTurin, Turin, Italy
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