Muscular Activity During Uphill Cycling.pdf

Available online at www.sciencedirect.com

Journal of Electromyography and Kinesiology 18 (2008) 116–127

www.elsevier.com/locate/jelekin

Muscular activity during uphill cycling: Eﬀect of slope, posture,

hand grip position and constrained bicycle lateral sways

S. Duc a, * , W. Bertucci b , J.N. Pernin a , F. Grappe a

a Laboratoire FEMTO-ST (UMR CNRS 6174), D´partement de M´canique Appliqu´e, Universit´ de Franche-Comt´ ,

24 Rue de l’Epitaphe 25000 Besan¸on, France

Laboratoire d’Analyse des Contraintes M´caniques – EA 3304 LRC CEA/UFR STAPS, Universit´ de Reims Champagne-Ardenne,

Campus Moulin de la Housse (b ˆ timent 6), 51100 Reims, France

Received 6 June 2006; received in revised form 26 September 2006; accepted 26 September 2006

Abstract

Despite the wide use of surface electromyography (EMG) to study pedalling movement, there is a paucity of data concerning the mus-

cular activity during uphill cycling, notably in standing posture. The aim of this study was to investigate the muscular activity of eight

lower limb muscles and four upper limb muscles across various laboratory pedalling exercises which simulated uphill cycling conditions.

Ten trained cyclists rode at 80% of their maximal aerobic power on an inclined motorised treadmill (4%, 7% and 10%) with using two

pedalling postures (seated and standing). Two additional rides were made in standing at 4% slope to test the eﬀect of the change of the

hand grip position (from brake levers to the drops of the handlebar), and the inﬂuence of the lateral sways of the bicycle. For this last

goal, the bicycle was ﬁxed on a stationary ergometer to prevent the lean of the bicycle side-to-side. EMG was recorded from M. gluteus

maximus (GM), M. vastus medialis (VM), M. rectus femoris (RF), M. biceps femoris (BF), M. semimembranosus (SM), M. gastrocne-

mius medialis (GAS), M. soleus (SOL), M. tibialis anterior (TA), M. biceps brachii (BB), M. triceps brachii (TB), M. rectus abdominis

(RA) and M. erector spinae (ES). Unlike the slope, the change of pedalling posture in uphill cycling had a signiﬁcant eﬀect on the EMG

activity, except for the three muscles crossing the ankle’s joint (GAS, SOL and TA). Intensity and duration of GM, VM, RF, BF, BB,

TA, RA and ES activity were greater in standing while SM activity showed a slight decrease. In standing, global activity of upper limb

was higher when the hand grip position was changed from brake level to the drops, but lower when the lateral sways of the bicycle were

constrained. These results seem to be related to (1) the increase of the peak pedal force, (2) the change of the hip and knee joint moments,

(3) the need to stabilize pelvic in reference with removing the saddle support, and (4) the shift of the mass centre forward.

Keywords: EMG; Pedalling–standing–seated-treadmill

1. Introduction

ing position. Cyclists often switch between seated and

standing posture during mountain climbing, notably to

decrease the strain of the lower back muscle. Standing is

used by the practitioners to relieve saddle pressure during

ﬂat terrain cycling and to increase power production during

sprinting. From our knowledge, only one study reported

EMG activity of lower limb muscles during standing posi-

tion ( Li and Caldwell, 1998 ). The authors showed that

EMG patterns of monoarticular extensor muscles, like M.

gluteus maximus (GM) and M. vastus medialis (VM) are

more aﬀected by the transition from seated to standing ped-

alling, than the biarticular ﬂexor muscles, i.e. M. biceps

The majority of cycling studies have examined muscular

activity of pedalling with using surface electromyography

(EMG), when subjects ride on horizontal surfaces. Up-to-

date, there is yet a lack of information concerning muscle

recruitment pattern of uphill cycling, especially in the stand-

* Corresponding author. Tel.: +33 3 81 66 60 37; fax: +33 3 81 66 60 00.

E-mail addresses: seb-duc@wanadoo.fr (S. Duc), william.bertucci@

univ-reims.fr (W. Bertucci), jean-noel.pernin@univ-fcomte.fr (J.N. Pernin),

frederic.grappe@univ-fcomte.fr (F. Grappe).

doi:10.1016/j.jelekin.2006.09.007

S. Duc et al. / Journal of Electromyography and Kinesiology 18 (2008) 116–127

117

femoris (BF) and M. gastrocnemius (GAS). These results

have been related to the changes of pedalling kinetics and

kinematics, which are due to the removal of the saddle sup-

port during standing pedalling and the forward horizontal

shift of the total body centre mass ( Alvarez and Vinyolas,

1999; Caldwell et al., 1998; Soden and Adeyefa, 1979; Stone

and Hull, 1993 ). Peak pedal force, crank torque and peak

ankle plantarﬂexor generated by cyclists are higher and

occur later during the downstroke ( Alvarez and Vinyolas,

1999; Caldwell et al., 1998 ). Moreover, while standing, the

extensor knee moment is extended longer into the down-

stroke (0–180) whereas the duration of the knee ﬂexor

moment is lower. Since the pattern of hip joint moment dis-

plays high similarity between the two postures ( Caldwell

et al., 1999 ), it has been suggested that changes of GM activ-

ity are linked to a decrease of the force moment arm and to

the pelvis stabilization ( Li and Caldwell, 1998 ).

The study of Li and Caldwell (1998) has three major lim-

its that should be considered. Firstly, the stationary cycling

ergometer (i.e. Velodyne) used by the authors to simulate

uphill conditions prevents the lateral sways of the bicycle

while standing pedalling. Therefore, EMG activity of biar-

ticular muscles might to be more altered by change of

cycling posture during ‘‘natural’’ standing pedalling since

it has been assumed that these muscles play a more complex

role during pedalling compared to monoarticular muscles.

Several studies ( Raasch et al., 1997; van Ingen Schenau

et al., 1992 ) suggested that biarticular muscles are responsi-

ble for the control of the direction of the force applied to the

pedal, the transfer of power produced by monoarticular

extensors muscles and the regularity of pedalling, notably

during the ﬂexion-to-extension transition (called top dead

centre, i.e. TDC) and during the extension-to-ﬂexion transi-

tion (called bottom dead centre, i.e. BDC).

Secondly, the response of other muscles involved during

pedalling, i.e M. semimembranosus (SM), M. semitendino-

sus (ST) and M. soleus (SOL), to the change of posture dur-

ing uphill cycling is unknown. It is not sure that SM and ST

patterns during standing pedalling are similar to BF pattern

because it has been suggested that these muscles, unlike to

BF, work more as knee ﬂexor than knee extensor ( Ericson,

1988 ). Moreover, the measure of the EMG activity of SOL

could allow to validate the hypothesis proposed by Li and

Caldwell (1998) that the increase of peak plantar ﬂexor

moment, observed during standing pedalling, is linked to

the activity of SOL and unrelated to the activity of GAS.

This may be caused by the biarticular function of GAS, as

it also serves as a knee ﬂexor. With the extended period of

the knee extensor moment during standing, increased

GAS activity would be contraindicated.

Thirdly, previous authors have not clearly reported the

upper body and trunk muscles activity during standing

pedalling. It is surprising because these muscular groups

seems to be greatly activated during standing pedalling,

notably to support additional weight due to the loss of sad-

dle support, to stabilize pelvis and trunk to control body

balance and to swing the body and the bicycle side-to-side.

During standing pedalling, cyclists can grip the handle-

bar on the brake levers (top hand position) or on the drops

of the handlebar (bottom hand position). The top hand

position is often used during climbing whereas the bottom

hand position is generally employed for sprints. Pedalling

biomechanics can be aﬀected by change of hand grip since

the trunk is more ﬂexed in the bottom hand position. Savel-

berg et al. (2003) observed signiﬁcant changes of EMG

activity of GM and TA muscles when the trunk is ﬂexed

20 to forward during seated pedalling. This eﬀect could

be increased during standing pedalling because the trunk

ﬂexion is higher when the hands are placed on the drops

of the handlebar. At our knowledge, no study has com-

pared the eﬀect of the two hand grip positions during

standing pedalling on muscular activity.

It was suggested that change of road slope or gradient can

aﬀect kinetics and kinematics of pedalling. In the case of

uphill cycling, the orientation of the rider and bicycle with

respect to the gravity force may enhance some modiﬁcations

of the pedalling technique. Caldwell et al. (1998) showed

that cyclists produce a greater crank torque during the ﬁrst

120 of the crank cycle and during the ﬁrst half of the

upstroke (180–270) at 8% slope compared to 0%. These

force changes are combined with the alteration of the pedal

orientation to a more ‘‘toe-up’’ position. The same authors

( Caldwell et al., 1999 ) have also found that the peak ankle

plantarﬂexor and the peak knee extensor moments are

higher and occur slightly earlier in the crank cycle at 8%

slope. However, all these changes are largely explained by

the diﬀerence in the pedalling cadence from the 0% slope

(82 rpm) to 8% slope (65 rpm) condition. While cadence

decreased, total work done per crank revolution increased

a consequence of holding power output constant. The eﬀect

of the slope on muscular activity is ambiguous. Li and Cald-

well (1998) have not found diﬀerences in EMG activity of six

lower limb muscles between 0% and 8% slope whereas

Clarys et al. (2001) observed a signiﬁcant increase in EMG

activity of lower limb (sum of EMG activity of VM, BF,

TA, GAS) with increasing slope (2–12%). Diﬀerences could

be due to the cycling experience level of the subjects (stu-

dents with 2 years of cycling experience vs professional

cyclists), the experimental context of the two studies (lab

vs ﬁeld, respectively) and to the analysis of EMG data (indi-

vidual vs global activity, respectively). It is also important to

remember that, as throughout studies of Caldwell et al.

(1998, 1999) , subjects did not use the same pedalling cadence

between the two slope conditions during the ﬁrst study. The

eﬀect of the increase in slope on EMG activity could be

masked by the decrease of pedalling cadence since many

studies have shown that intensity of EMG activity of GM,

RF, GAS and BF changes across pedalling cadence ( Baum

and Li, 2003; Marsh andMartin, 1995; Neptune et al., 1997;

Ryschon and Stray-Gundersen, 1991; Sarre et al., 2003 ).

The purpose of this study is to quantify the inﬂuence of

(1) the slope (4–7–10%); (2) the pedalling posture (seated–

standing); (3) the hand grip position in standing pedalling

(on the brake levers–on the drops); and (4) the constrained

118

S. Duc et al. / Journal of Electromyography and Kinesiology 18 (2008) 116–127

lateral sways of bicycle in standing pedalling (ride on a sta-

tionary ergometer), on the intensity and the timing of

EMG activity of lower limb, trunk and arm muscles. More

speciﬁcally, four hypotheses were tested. Firstly, muscular

activity of power prime producer muscles (GM, VM),

lower back muscles and arm muscles would increase line-

arly with the treadmill slope due to the change of rider ori-

entation respect to gravity force. Secondly, standing

pedalling would aﬀect considerably both intensity and tim-

ing of hip extensor and ﬂexor muscles (GM, BF), trunk

and arm muscles, since this posture removes the saddle

support. Thirdly, grip of the handlebar on the drops during

standing pedalling would also change EMG activity of

trunk and arm muscles since the total body centre mass

is shifted forward in this position compared to the brake

levers hand grip position. Finally, contrary to Caldwell

et al. (1998, 1999) and Li and Caldwell (1998) , we hypoth-

esized that lateral sways of the bicycle in standing are not

insigniﬁcant. Intensity of EMG activity of lower limb mus-

cles would increase when cyclists pedal in standing on a sta-

tionary ergometer that constrains bicycle tilts.

A magnet (Sigma Sport, Neustadt, Germany) was ﬁxed on the

bicycle near the bottom bracket in order to isolate each pedal

cycle. The magnet signal was then recorded with the ampliﬁer

used for the EMG collection.

2.3. Data collection and processing

2.3.1. EMG recording

The EMG activity from eight muscles of the right lower limb

(M. gluteus maximus (GM), M. vastus medialis (VM), M. rectus

femoris (RF), M. biceps femoris caput longum (BF), M. semi-

membranosus (SM), M. gastrocnemius medialis (GAS), M. soleus

(SOL), M. tibialis anterior (TA)), from two muscles of the trunk

(M. rectus abdominis (RA), M. erector spinae (ES)) and from two

muscles of the right arm (M. biceps brachii (BB) and M. triceps

brachii (TB)) were collected during the second test session. In

order to limit the potential crosstalk between SOL and GAS

activity, two surface electrodes for SOL were positioned on the

lower third of the calf, just above the Achilles tendon. Data col-

lection occurred during the ﬁnal 15 s of each pedalling trial and

lasted for ﬁve pedal cycles per collection period. The subjects were

kept unaware of the exact timing of data collection.

The EMG sensors were conformed to recommendations of the

SENIAM. Recorded sites were shaved and cleaned with an alcohol

swab in order to reduce skin impedance to less than 10 kX. Pairs of

silver/silver-chloride, circular, bipolar, pre-gelled surface electrodes

(Control Graphique Medical, Brie-Comte-Robert, France) of

20 mm diameter, were applied on the midpoint of the contracted

muscle belly ( Clarys, 2001 ), parallel to the muscle ﬁbbers, with a

constant inter-electrode distance of 30 mm. The reference elec-

trodes were placed over electrically neutral sites (scapula and

clavicle). All the electrodes and the wires were ﬁxed on the skin with

adhesive pads to avoid artifacts. EMG was recorded with a MP30

ampliﬁer (Biopac System, Inc., Santa Barbara, USA, common

mode rejection ratio >90 dB, input resistance is in order of 10 9 X).

The EMG signals were ampliﬁed (gain = 2500), band pass ﬁltered

(50–500 Hz) and analog-to-digital converted at a sampling rate of

1000 Hz. We chose a high-pass frequency of the EMG bandpass

ﬁlter (50 H) in order to eliminate the ambient noise caused by

electrical-power wires and components of the motorised treadmill.

The raw EMG were expressed in root mean square (RMS)

with a time averaging period of 20 ms. The overall activity level of

each muscle was identiﬁed by the mean RMS calculated for ﬁve

consecutives crank cycles (EMG mean ) and normalised to the

maximal RMS value measured for each muscle and for each

subject during all the trials (normalisation to the highest peak

activity in dynamic condition). The EMG signal was also full-

wave rectiﬁed and smoothed (Butterworth ﬁlter, second-order,

cut-oﬀ frequency of 6 Hz) to create the linear envelope. Using the

magnet signal, the linear envelope was then divided into each of

the ﬁve pedal cycles and a mean linear envelope was computed for

each muscle. Finally, the linear envelopes of each muscle were

scaled to a percentage of the maximum value found for each

individual muscle and for each subject.

To analyse the muscle activity pattern, ﬁve parameters were

calculated from the linear envelope for each pedalling trial: EMG

burst onset (EMG onset ), oﬀset (EMG oﬀset ) and peak timing

(EMG peak-timing ), EMG burst duration (EMG duration ), and peak

EMG burst magnitude (EMG peak ). An arbitrary threshold value

of 25% of the maximum value across conditions was chosen to

determine the onset and the oﬀset of EMG burst, like that selected

by Li and Caldwell (1998) . Visual inspection determined if this

2. Methods

2.1. Subjects

Ten trained, healthy, male, competitive cyclists of the French

Cycling Federation volunteered to participate in this study. They

were classiﬁed in national (n = 4), regional (n = 4) or depart-

mental (n = 2) category and had regularly competed for at least

two years prior the study. Before the experiment, each subject

received full explanations concerning the nature and the purpose

of the study and gave written informed consent. Age, height, and

body mass of the tested subjects were 28 ± 7 (mean ± SD) yr,

1.78 ± 0.07 m, and 71 ± 8 kg, respectively.

2.2. Protocol

Each cyclist performed two test sessions in our laboratory. The

ﬁrst test session was an incremental test to exhaustion to deter-

mine maximal aerobic power (MAP), maximal oxygen uptake

ð VO 2max Þ and maximal heart rate (HR max ). The second test ses-

sion consisted of four pedalling sessions of eight randomised trials

with diﬀerent uphill cycling conditions. Both test sessions were

held within a period of 1 week and separated by at least 2 days.

Each subject cycled with his own racing bicycle on a large

motorised treadmill (S 1930, HEF Techmachine, Andr´zieux-

Bouth´on, France) of 3.8 m length and 1.8 m wide. Before testing,

all the subjects performed several sessions on the motorised

treadmill to acclimatise themselves to the equipment. Throughout

the tests, the subjects were attached with a torso harness for their

safety without hindering the riders motion nor position on the

bicycle. All the bicycles were equipped with clipless pedals. The

bicycle tyre pressure was inﬂated to 700 kPa. The rear wheel was

ﬁtted with the PowerTap hub (professional model, CycleOps,

Madison, USA) to measure the power output (PO), the velocity

and the pedalling cadence (CAD) during the two test sessions.

This system uses the strain gauge technology (eight gauges). The

validity and the reproductibility of the PowerTap hub

were showed by Bertucci et al. (2005) and Gardner et al. (2004) .

S. Duc et al. / Journal of Electromyography and Kinesiology 18 (2008) 116–127

119

threshold was appropriate. Appropriate thresholds reﬂected easily

identiﬁable onset and oﬀset points and minimal discrepancies in

identifying non-meaningful burst. In the case that 25% was con-

sidered inappropriate, the threshold was raised to 35% and more,

of the maximum value across conditions. Upon reaching the

determined threshold, the muscle was considered active, and the

muscle burst duration was deﬁned as the duration, in degrees, of

the crank angle between the onset and oﬀset value. EMG peak was

the maximum value from the linear envelope during each pedal-

ling trial. EMG peak-timing was the crank angle at which the peak

EMG occurred.

Finally, we have determined the global EMG activity

(EMG global ) of the lower limb and the upper limb with adding the

EMG mean of eight lower limb muscles (GM, VM, RF, BF, SM,

GAS, SOL, TA) and of the trunk and arm muscles (RA, ES, BB,

TB).

(2005) . Brieﬂy, the rear wheel of the bicycle was ﬁxed by a quick

release skewer in the stand of the ergometer. This stand constrains

lateral motions of the rear wheel. A roller, which was connected

with a ﬂywheel in an electromagnetic resistance unit, was brought

in contact with the tyre to provide a resistive force.

The PO (80% of MAP) was kept constant during the eight

trials. The CAD diﬀered between cyclists (range: 60–70 rpm) but

not between the trials. Each cyclist was required to perform four

times 8 pedalling trials (4S, 7S, 10S, 4ST, 7ST, 10 ST, 4ST b ,

4ST c ) since our EMG measurement device can collect only three

EMG signals at the same time. So, in order to minimise the

muscular fatigue, we ﬁxed the time of each trial at 1 min. Trials

were separated by 3 min of low active recovery (PO < 40%

MAP). The recovery between two-8 pedalling trials due to the

change of the EMG electrodes conﬁguration was higher and

passive (10–15 min).

2.3.2. Video recording

Bicycle lateral sways were recorded simultaneously with EMG

data at 50 Hz using a JVC video camera (JVC, Yokohama,

Japan), with the lens axis oriented parallel to the rear frontal of

the subject, positioned 4 m behind the rider. The maximal tilt

angle (TILT angle ) of the bicycle was determined for each pedalling

condition with averaging maximal values measured during 30 s.

2.6. Statistical analyses

All data were analysed using the Sigmastat statistical program

(Jandel, Germany, version 2.0) for Windows. The data were tested

for normality and homogeneity of variance (Kolmogorov–Smir-

nov tests) and turned out to be not normally distributed. Thus, a

no-parametric two way (3 slopes · 2 postures) repeated measures

factorial analysis of variance (ANOVA on ranks) was used to

detect signiﬁcant diﬀerences of each dependent variable (EMG mean ,

EMG onset ,EMG oﬀset ,EMG peak-timing ,EMG duration ,EMG peak ,

EMG global , TILT angle ). Tukey’s HSD post hoc analysis was per-

formed when ANOVA on ranks indicated a signiﬁcant diﬀerence.

The Wilcoxon signed rank test was also employed to determine

the eﬀect of the change of hand position (top to bottom) during

standing pedalling and the inﬂuence of the constrained bicycle

lateral sway on the same variables. The results were expressed as

means ± standard deviation (SD). The level of signiﬁcance was set

at p < 0.05.

2.4. First test session: incremental test

After a brief warm-up period ( 5 min), the incremental test

started at 130 W for 2 min. The treadmill slope at this ﬁrst stage

was ﬁxed to 1%. The treadmill velocity was determined for each

cyclist with using a mathematical power model, in order to obtain

the initial PO (130 W). The workload was then increased by

30 W every 2 min until the subject became exhausted, by

increasing the treadmill slope by 0.5% during each increment. The

treadmill velocity was unchanged throughout the incremental test.

The cyclists were required to remain in a seated position during

the entire test, and could choose themselves their CAD by

adjusting the bicycle gears. The MAP was determined as the mean

PO maintained during the last completed workload stage. A K4b 2

breath-by-breath portable gas analyser (Cosmed, Rome, Italy)

and a chest belt (Polar, Kempele, Finland) were used to collect the

metabolic and the HR data. The Cosmed K4b 2 system was cali-

brated using the manufacturer’s recommendations. The highest

mean VO 2 and HR values obtained during the increment test for

10 s were deﬁned, respectively, as the VO 2max and the HR max .

3. Results

Table 1 displays the results obtained during the incre-

mental test to exhaustion. The physiological characteristics

of subjects were common to those obtain with studies using

similar cyclists groups ( Bertucci et al., 2005; Marsh and

Martin, 1995; Millet et al., 2002; Sarre et al., 2003 ).

Muscle activity patterns when standing pedalling with

griping the handlebar on the drops or with constrained

bicycle tilts were similar of the 4ST condition (hand on

the brake levers and with bicycle tilting). So we decide to

represent in Fig. 1 only the muscle activity patterns with

ensemble linear envelopes of the six other cycling condi-

tions (3 slopes (4–7–10%) · 2 postures (S, ST)). The pattern

of EMG activity of lower limb muscles in seated posture

agreed with those generally reported in similar cycling

2.5. Second test session: uphill conditions

After a short self-selected warm-up period ( 10 min), each

cyclist performed six pedalling trials (4S, 7S, 10S, 4ST, 7ST, 10ST)

with diﬀerent slopes (4%, 7% and 10%), and pedalling postures

(seated (S) and standing (ST)). For all these pedalling trials, the

hands were positioned on the top of the handlebar (on the brake

levers). Two additional pedalling trials were performed in stand-

ing position and against the 4% slope, to test the eﬀect of the

bottom hand position (4ST b ) and the eﬀect of the constrained

bicycle lateral sways (4ST c ). The eight pedalling trials were per-

formed in a randomised order. For the 4ST c condition, the cyclists

were required to pedal with their bicycle on a stationary Axiom

PowerTrain ergometer (Elite, Fontaniva, Italy), which was

mounted on the inclined motorised treadmill. The Axiom Power

ergometer has been recently described in detail by Bertucci et al.

Table 1

Physiological characteristics of subjects obtained during the incremental

test to exhaustion

VO 2max ð lmin 1 Þ VO 2max ð lmin 1 kg 1 Þ MAP (W) HR max (bpm)

4.5 (0.4) 66 (6) 378 (47) 183 (8)

Values are means (+SD). VO 2max , maximal oxygen uptake; MAP, maxi-

mal aerobic power; HR max , maximal heart rate.

120

S. Duc et al. / Journal of Electromyography and Kinesiology 18 (2008) 116–127

the GM occurred earlier in the crank cycle for 7% slope

(134 ± 61) compared to 4% (187 ± 90) and 10% slope

(166 ± 72). The EMG peak of ES in seated pedalling tended

(p = 0.06) to increase with the slope (27 ± 9% for 4% and

7% slope to 29 ± 11% for 10% slope). The EMG global of

the lower limb and the EMG global of the upper limb were

not aﬀected by the changes of the slope whatever the ped-

alling posture used. TILT angle of the bicycle in standing

pedalling increased signiﬁcantly with the slope: 8 ± 3 for

4%, 9 ± 4 for 7% and 11 ± 1 for 10% slope.

3.2. Eﬀect of the pedalling posture

Unlike the slope, the change of the posture aﬀected

greater both the intensity and the timing of the EMG activ-

ity of all the muscles, except those crossing the ankle’s joint

(GAS, SOL, TA).

3.2.1. EMG intensity

Tables 2 and 3 display the EMG mean and the EMG peak

values for each muscle across the two posture conditions.

Table 2

Mean EMG activity per cycle (EMG mean ) across posture conditions for all

subjects, expressed as a percentage of the maximum value of each muscle

Postures

Seated (%)

Standing (%)

19 (3)

26 (5) a

29 (6)

34 (6) a

26 (7)

33 (8) a

25 (6)

29 (7) a

32 (10)

26 (5) a

GAS

34 (7)

35 (9)

SOL

36 (7)

37 (9)

37 (10)

35 (9)

11 (2)

21 (3) a

14 (4)

25 (6) a

17 (7)

33 (6) a

25 (7)

39 (8) a

Fig. 1. Mean ensemble curves of EMG linear envelopes across slope

(unbroken line) and postures (dashed line) conditions for gluteus maximus

(GM), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF),

semimembranosus (SM), gastrocnemius (GAS), soleus (SOL), tibialis

anterior (TA), rectus abdominis (RA), erector spinae (ES), biceps brachii

(BB) and triceps brachii (TB). 4S: 4% slope seated; 7S: 7% slope seated;

10S: 10% slope seated; 4ST: 4% slope standing; 7ST: 7% slope standing;

10ST: 10% slope standing. The crank angle represents TDC to next TDC,

0–360. EMG curves for each subject were scaled to the maximum value

observed across all conditions.

Values are means (+SD).

Indicate signiﬁcant diﬀerence between the two postures conditions.

Table 3

Mean peak of EMG activity per cycle (EMG peak ) across posture

conditions for all subjects, expressed as a percentage of the maximum

value of each muscle

Postures

Seated (%)

Standing (%)

42 (14)

55 (13) a

63 (10)

67 (7)

61 (13)

67 (9) a

47 (11)

54 (9) a

condition ( Baum and Li, 2003; Ericson, 1988; Li and Cald-

well, 1998; Neptune et al., 1997; Raasch et al., 1997 ).

62 (14)

45 (12) a

GAS

66 (13)

67 (9)

SOL

71 (10)

74 (10)

3.1. Eﬀect of the slope

65 (13)

62 (12)

20 (3)

45 (8) a

27 (10)

55 (13) a

The intensity and the timing of EMG activity of all the

muscles were not signiﬁcantly diﬀerent between the three

slopes studied, except for the GM and the ES muscles. When

the subjects pedalled in standing posture, the EMG peak of

26 (6)

62 (9) a

46 (11)

70 (8) a

Values are means (+SD).

Indicate signiﬁcant diﬀerence between the two postures conditions.

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: