An isometric maximal voluntary contraction (iMVC) is mostly used for the purpose of EMG normalization, a procedure described in the scienti.c literature in order to compare muscle activity among di.erent muscles and subjects. However, the use of iMVC has certain limitations. The aims of the present study were therefore to propose a new method for the purpose of EMG amplitude normalization in cycling and assess its reliability. Twenty-three cyclists performed 10 trials of a maximal isokinetic protocol (MIP) on a cycle ergometer, then another four sub-maximal trials, whilst the EMG activity of four lower limbs muscles was registered. During the 10 trials power output (CV = 2.19) and EMG activity (CV between 4.46 and 8.70) were quite steady. Furthermore, their maximal values were reached within the 4th trial. In sub-maximal protocol EMG activity exhibited an increase as a function of exercise intensity.
MIP entails a maximal dynamic contraction of the muscles involved in the pedalling action and the normalization session is performed under the same biomechanical conditions as the following test session. Thus, it is highly cycling-speci.c.
MIP has good logical validity and within-subject reproducibility. Three trials are enough for the purpose of EMG normalization in cycling. © 2007 Elsevier Ltd. All rights reserved.
Keywords: Surface electromyography; Maximal dynamic exercise; Sub-maximal dynamic exercise; Reproducibility; SRM ergometer
1. Introduction

Surface electromyography (EMG) is a non-invasive method used to obtain information on muscle activity. Absolute EMG amplitude level is of interest, for instance, in clinical studies, since patients usually can not perform maximum contractions(van Diee¨net al., 2003), or to make di.erencesin EMG activitybetweena pain anda non-pain group come to light (Dano., 1986). However, absolute EMG values depend on many factors unrelated to the level of muscle activation (e.g. van Diee¨n et al., 2003). It is widely accepted that a procedure of EMG amplitude nor­
* Corresponding author. Address: Istituto di Ricerca sull’Attivita` Motoria, Universita` degli Studi di Urbino ‘‘Carlo Bo”, Via I Maggetti, 26/2, 61029 Urbino, Italy. Tel.: +39 0722 303413; fax: +39 0722 303401.
E-mail address: m.ditroilo@uniurb.it (M. Ditroilo).
malization is required in order to: (i) make a between-and within-subject comparison of activation level in work­ing muscles (Bolgla and Uhl, 2007; Lehman and McGill, 1999; Mirka, 1991), (ii) facilitate comparison between two di.erent muscles, or right and left side muscles of the same subject (Lehman and McGill, 1999), (iii) allow for comparisons between di.erent joint angles, namely di.er­ent speci.c positions throughout the range of motion of a joint(Mirka, 1991), (iv) compare results with similar data from other studies(SoderbergandKnutson, 2000).
Most published studies have used an isometric maximal voluntary contraction (iMVC) for the purpose of EMG normalization (Arokoski et al., 1999; Lobbezoo et al., 1993; Smith et al., 2004). Although this method has been demonstrated to be reliable(Dankaerts et al.,2004; Kollm­
itzer et al., 1999), it is strongly dependent on the speci.c joint angles used during the iMVC. In fact, an EMG signal
1050-6411/$ -see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jelekin.2007.11.013

collected during an iMVC performed at a reference joint angle should be used only for normalization of muscle activity recorded at the same speci.c joint angle, otherwise a considerable error can occur (Enoka and Fuglevand, 1993; Mirka, 1991). A second potential limitation is the assumption that subjects can actually perform an e.ort involving maximal force generation, especially if they are not trained and well motivated.
The use of normalization to sub-maximal isometric con­traction is present in studies conducted with the patient population and when assessing low level of muscle activity (Dankaerts et al., 2004; Hunt et al., 2003). This method was found to be even more reliable, compared to iMVC, in between-days repeated measures, although the correct determination of relative sub-maximal loads for every mus­cle is di.cult(Dankaerts et al., 2004).Moreover, the EMG associated with a dynamic activity has also been proposed as reference value (e.g. Prilutsky et al., 1998).
The problem of a correct selection of an EMG normal­ization procedure is essential.A recent paper(Rou.et and Hautier, 2007)has widely addressed this issue. The authors underlined that while executing a speci.c task, physiologi­cal modi.cations in the neural drive should be re.ected in the EMG signal. Other authors pointed out that when deal­ing with sports movements the electromyogram should be the expression of the dynamic involvement of speci.c mus­cles(Clarys andCabri, 1993). In cycling, EMG is often per­formed in order to assess the muscular intervention during the pedalling action. For the normalization purpose it is therefore pivotal to choose a meaningful reference contrac­tion so that its activation is regulated by the same neuro­muscular pattern as the pedalling action. This means that the task parameters of the reference contraction (e.g. move­ment amplitude, joint position, speed, etc.) should repro­duce, as much as possible, the pedalling action (Latash, 1998).
Despite the above considerations, several studies exam­ining cycling have improperly implemented EMG normal­ization using an iMVC as a reference contraction, and then expressing the dynamic EMG activity as a percentage of it (Ericson, 1986; Ericson et al., 1985; Hautier et al., 2000; Marsh and Martin, 1995; Neptune et al., 1997). In 2002, Hunter et al. publishedapaper comparing four normaliza­tion protocols: three of them involved an iMVC, the fourth a dynamic pedalling action against a constant load, which was repeatedly increased until the subject could no longer complete a full revolution of the pedal. The authors found that the iMVC test performed on an isometric leg extension dynamometer yielded the highest iEMG amplitude values and concluded suggesting that, for this reason, the use of iMVC as a normalization procedure for dynamic cycling activity would be better. This assumption, however, has been recently questioned since the reference EMG signals collected during iMVC can hardly represent the maximal neural drive obtained during cycling(Rou.et and Hautier, 2007). Furthermore, other authors compared the EMG amplitude signal during iMVC and maximal dynamic cycling contractions(Hautier et al., 2000; Rou.et and Hau­
tier, 2007)and found that the electrical activity of some of the analysed muscles were not signi.cantly di.erent between the two methods, or even higher when the dynamic contraction was used.
More recently, alternative dynamic methods for the EMG normalization in cyclinghave been proposed. Takai­
shi et al. (1998) set the integrated EMG corresponding to the lowest cadence (45 rpm) as reference value, while Hug et al. (2004b) normalized the vastus lateralis EMG activity witha40Wintensityexercise. However,it couldbe argued that due to the low intensity chosen, the muscular recruit­ment pattern could be quite di.erent from a pedalling action at higher intensity; furthermore, the vastus lateralis activity at 40W intensity is probably not di.erent from baseline.
Neptune and Herzog (2000), assessing the adaptation of muscle coordination when traditional and elliptical chain-rings were adopted, used the highest EMG value observed across all trials for normalization purposes. Since the experimental design entailed a variation of pedalling bio­mechanical conditions (e.g. instantaneous crank angular velocity), the normalization procedure chosen could not represent all the di.erent tests performed.
Hug et al. (2004a)and Laplaud et al. (2006) normalized the EMG of a graded pedalling exercise as a percentage of the highest intensity step. Interestingly, Taylor and Bronks (1995) showed that the reference EMG amplitude value (a maximal ‘‘unfatigued” EMG value obtained by rapidly increasing the resistance until the subject could no longer maintain the .xed cadence) was about twice than the one reached during the last step of the graded exercise. It could be maintained therefore that when the EMG reference value is the latter, a normalization to a sub-maximal dynamic contraction is performed and the limit of this procedure, as previously reported, is the determination of equivalent sub-maximal e.orts for di.erent muscles (Dankaerts et al., 2004; Marras and Davis, 2001)and subjects.
Several methods have been proposed for the purpose of EMG amplitude normalization in cycling but, based on the above evidence, the best reference contraction to use is still controversial. Methods grounded on iMVC or sub-maxi­mal dynamic contractions have evidenced limitations. Accordingly, the main aim of this paper was to present a maximal isokinetic protocol (MIP) as a new method for the purpose of EMG normalization in cycling. Brie.y, this protocol should produce a maximal dynamic contrac­tion of the muscles involved in the pedalling action. Furthermore, the normalization session is performed under the same biomechanical conditions as the following test session, thus making the protocol highly speci.c. It is therefore hypothesized that the cyclists do not need to learn the required task as it is inherent in their pedalling patterns.
The second aim of this investigation was to detect the intra-individual variability of the method proposed.

E. Ferna´ ndez-Pen˜a et al./Journal of Electromyography and Kinesiology xxx (2008) xxx–xxx 3
2. Methods

2.1. Subjects

Twenty-three recreational and competitive healthy male cyclists (age 29.3±9.0 yr, height 177.5±7.4 cm, weight
71.6±9.8 kg) volunteered and gave their written informed con­sent to participate in the study, which was previously approved by the Human Ethics Committee of the University of Urbino (Italy). All the cyclists used to train about 10h per week with a quite homogeneous training programme. Competitive cyclists, unlike recreational ones, competed during weekends at Masters level. They all had covered an average of 9000 km during the last sea­son. None of them had previous experience in riding an isokinetic cycle ergometer, and they were asked to refrain from exhausting exercise 24h before testing.
2.2. Exercise protocol

An SRM ergometer (Schoberer Rad Meßtechnik SRM GmbH, Ju¨ lich, Germany) was used for all tests, mounted with the two .ywheels and in the ninth gear. The SRM crankset, equipped with strain gauges, directly measured the torque produced by the force applied to the pedals perpendicularly to the crank length. The ergometer was customized with subject’s own bicycle’s mea­sures and clipless pedals. A display was available close to the handlebars of the ergometer to let the cyclists check their pedal­ling cadence.
2.2.1. Warm up

Cyclists performed a 10min warm up at a recommended cadence of 80 rpm. The power constantly increased from 75 to 200W during the .rst6min (25Wmin-1), the intensity was then set to 125W for the next2min and increased to 200 and 250W for the last 2min. Depending on the performance level of the subjects, the warm up intensity could be increased by no more than 25W per step.

2.2.2. Maximal isokinetic protocol (MIP)
MIP was performed in the isokinetic mode of the ergometer, at a .xed pedalling frequency of 80 rpm. This mode allows the subject to pedal without resistance up to the .xed cadence, while resistance is automatically and proportionally increased when the subject tries to overcome it. Prior to the maximal e.ort, cyclists pedalled at 80 rpm and low intensity (50–100 W) and at the signal they started to pedal as forcefully as possible for 6 s, while a vigorous verbal encouragement was given. They were instructed to remain seated and to hold the hands on the low part of the handlebars during the trial. Every cyclist completed a total of ten 6s all-out sprints. A full recovery was ensured by a 3min rest period between sprints, in which they were allowed to drink water and pedal at a low intensity.

2.2.3. Sub-maximal protocol (SMP)
AftertheMIP, cyclists restedfor10min, pedallingat50W at a freely chosen cadence. They were then asked to perform four sub-maximal exercises at 0%, 20%, 40% and 60% of the maximum power output obtained during the MIP. In order to perform the 0% exercise, the brake was turned o.. It is however useful to know that, due to the friction of the moving parts, the workload was actually about 30–35 W. Concerning the other sub-maximal exercises, while the subject was pedalling at 50 W, the load was increased and as soon as a steady pedalling cadence of 80 rpm was reached, data were collected for 20 s. Trials were separated by a 2min active rest period. The 80% intensity was too demanding to be maintained for at least 20 s, hence it was not included in the SMP.
2.3. Recording of EMG and angular crank position
Following the recommendations of the SENIAM project (Freriks et al., 1999), EMG of four muscles of the right leg was recorded during the MIP and the SMP. The selected muscles were vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius lateralis (GL). Skin was shaved, slightly abraded with sandpaper and cleaned with alcohol. Ag/AgCl bipolar electrodes (Blue Sensor N-00-S, Ambu Medicotest A/S, Ølstykke, Denmark) were placed over the muscle belly of selected muscles at an interelectrode distance of 20 mm. To avoid artefacts from lower limb movements, the wires connecting electrodes were well secured with tape.
Signal was ampli.ed at a gain of 600. Common mode rejection rate and input impedance were respectively 95 dB and 10GX. Raw electromyographic data were band-pass .ltered using a fourth order Butterworth .lter, with cut-o. frequencies of 10 and 350 Hz. Fig. 1 depicts an individual example of the raw EMG signals as a function of time, related to the four analysed muscles.
In order to measure the instantaneous angular position of the crank, a rotational encoder (EL40B, Eltra, Sarego (VI), Italy) with a resolution of 2000 pulses per turn was coupled to the left crank of the ergometer by a chain drive. Since the gear ratio between the gear wheel of the left crank and the sprocket of the encoder was 53/15, the total resolution of the system was 7066.7 pulses per pedal cycle(Picture1).
The EMG and angular position of the crank signals were synchronized, sampled at 1000 Hz and stored on a PC using a 16 bit A/D converter data acquisition system (APLabDAQ, APLab, Rome, Italy).

Fig. 1. Raw EMG signals from a single, representative trial recorded during the maximal isokinetic protocol. The window corresponding to a pedal cycle is also shown. VL = vastus lateralis; BF = biceps femoris; TA = tibalis anterior; GL = gastrocnemius lateralis.

Picture 1. A rotational encoder was coupled to the left crank of the SRM ergometer in order to measure the instantaneous angular position of the crank and synchronize it with the EMG activity.
2.4. Data processing
Torque applied to the crankset during the MIP was recorded at 200 Hz for power output calculation purposes. Average power output of each maximal trial (PO) was calculated as the product of the average torque over the6 s (in Nm) and the actual average cadence (in rad/s). For each subject, the best PO (POB)was set to represent 100% and the other trials were calculated as a per­centage of POB.
Raw EMG data were processed by root mean square (RMS) determination for each complete cycle, de.ned as a full revolution of the right crank from top dead center (TDC at 0°)to the next TDC. The mean RMS was calculated averaging the RMS values of the eight pedal cycles completed in every MIP trial, and aver­aging the complete pedal cycles of the last 10 s (about 13 pedal cycles) in every SMP trial.
For MIP assessment, the highest EMG activity achieved for each muscle was set to 100% and the other trials were calculated as a percentage of the highest. In contrast, for SMP assessment, the EMG activity of all muscles corresponding to POB was set to 100% and the values obtained during the submaximal exercises (0%, 20%, 40% and 60% of POB)were expressed as a percentage

Fig. 2. Example of individual muscle activity, as a function of crank angle, obtained at .ve di.erent intensities for the vastus lateralis (A), biceps femoris (B), tibialis anterior (C) and gastrocnemius lateralis (D).

E. Ferna´ ndez-Pen˜a et al./Journal of Electromyography and Kinesiology xxx (2008) xxx–xxx 5
of the former. An example of individual EMG patterns obtained for the four analysed muscles is represented in Fig. 2. The raw data were root mean squared with a moving window length of 100 ms.
2.5. Statistical analysis

In order to evaluate the within-subject reproducibility of PO and EMG for the four muscles analysed, the variables were checked for normality and homoscedasticity and were log-trans­formed when these assumptions were violated. Thereafter the intra-subject standard error of measurement (SEM), the coe.­cient of variation (CV) and the intra-class correlation coe.cient (ICC) were calculated as proposed by Hopkins (2000) with the assistanceofa reliability spreadsheet(Hopkins, 2007). TheCVis

p..
SD= 2

de.ned as 100 ·ðe-1Þ, where SD is the standard deviation of the change scores of natural log of the measure. The ICC is de.ned as (V -v)/V, where V is the between-subject variance averaged over the two trials analysed, and v is the square of the standard error of measurement.
3. Results
Fig.3 shows PO (mean±SD) reached during the 10 tri­als. The POB (100%) was achievedduring the 4th trial. The PO values were, however, very close to each other, ranging from 98.0 to 100.0, thus indicating a quite high reproduc­ibility of the variable, with no observable learning or fati­gue e.ect. The POB obtained ranged from 664.6 to 1013.9W (data not shown).
EMG activity (mean±SD)is shown forVL(Fig.4A), BF(Fig.4B), TA(Fig.4C) and GL(Fig.4D), registered during the 10 trials. For each of the muscles included in the analysis, the 100% activity was achieved within the 3rd trial, although BF (Fig. 4B) and GL (Fig. 4D) tend to decrease thereafter.
Reliability measures from consecutive pairs of trials are summarized in Table 1. SEM and CV are presented as a mean value, whilst for ICC maximal and minimal values are shown. PO has the lowest CV (2.19), indicating very good consistency between repeated measures. Among the EMG activities, VL and TA show, respectively, the lowest (CV = 4.46) and the highest variability (CV = 8.70). ICCs in all the variables analysed, ranging from 0.922 to 0.994, are considerably high.

Fig. 4. EMG activity (mean±SD) for vastus lateralis (A), biceps femoris (B), tibialis anterior (C) and gastrocnemius lateralis (D) registered duringthe 10 trials of the maximal isokinetic protocol. The highest EMG activity was set equal to 100 and the other trials’ were calculated as a percentage of the best one.

Table 1 Statistical measures of reliability from consecutive pairs of trials
SEM (mean)  CV (mean)  ICC (range)
Power output (PO, Watt) VL EMG activity BF EMG activity GL EMG activity TA EMG activity  17.11 0.34 0.47 0.37 0.43  2.19 4.46 7.32 6.85 8.70  0.962–0.986 0.969–0.987 0.934–0.983 0.922–0.985 0.948–0.994

SEM and CV are expressed as a mean, whilst ICC as a range value.
VL = vastus lateralis; BF = biceps femoris; TA = tibialis anterior;
GL = gastrocnemius lateralis.
The EMG activity (AU) is the root mean square of the raw EMG data for
each complete pedalling cycle.
SEM = standard error of measurement; CV = coe.cient of variation;
ICC = intraclass coe.cient of correlation.

The EMG activity (mean±SD) corresponding to 0%, 20%, 40% and 60% intensities of POB is presented for VL (Fig. 5A), BF (Fig. 5B), TA (Fig. 5C), GL (Fig. 5D). A visual inspection showed a linear EMG activity increase when moving from 0% to 100% of exercise intensity, for VL (Fig. 5A), BF (Fig. 5B) and TA (Fig. 5C). GL (Fig. 5D) instead exhibited a curvilinear trend.
4. Discussion
The aim of this study was to propose a new method for EMG amplitude normalization in cycling and assess its reliability. Di.erent investigations suggesting isometric or sub-maximal dynamic contractions for EMG normaliza­tion in cycling have been gone over, and the limitations were highlighted.
AMIP was introduced as a reference contraction for the EMG normalization procedure. The task required, a max­imal 6-s pedalling action, and the submaximal cycling are comparable for at least three reasons: (a) the contribution of the muscles of the lower limb is similar for maximal sprint and submaximal bicycling conditions, as discussed by Rou.et and Hautier (2007); (b) mechanical conditions of the MIP and the following test session match com­pletely: pedalling frequency, posture and joint angle ranges of the cyclist (hip, knee, ankle), and type of muscular con­traction; (c) the muscles are activated at the same part of the pedalling cycle, as shown in the EMG pro.les(Fig.2).
The EMG activity registered during SMP supports the validity of the method proposed. Pedalling at 0%, 20%, 40% and 60% intensities of POB resulted in a coherent level of muscular activity, which altogether exhibited an increase as a function of exercise intensity.
Three of the muscles analysed (VL, BF and TA) showed a linear trend, whilst the GL had a curvilinear shape. This latter result was deemed to be due to the somehow unusual pedalling pattern when cycling at very low intensities. In fact, it seems that when riding at0W the cyclist hasto avoid pushing down the pedal during the downstroke in order to maintain the predetermined cadence and a rela­tively smooth pedal stroke, thus making the knee extensor muscles to remain inactive. GL instead is often overactive to counterbalance the knee extensor muscle inactivity and produce the little amount of power needed for keeping the .ywheel rotation. Eight of the 23 subjects showed a similar or even higher GL activity at 0% compared to 20%. These data suggest therefore that due to the high

Fig. 5. EMG activity (mean±SD) corresponding to 0%, 20%, 40% and 60% intensities of the best power output for vastus lateralis (A), biceps femoris (B), tibialis anterior (C) and gastrocnemius lateralis (D).

E. Ferna´ ndez-Pen˜a et al./Journal of Electromyography and Kinesiology xxx (2008) xxx–xxx 7
inter-subject variability in recruitment pattern of some muscles (e.g. GL) normalization methods based on low intensity reference contractions in cycling are questionable.
The activity of each muscle during submaximal contrac­tions is calibrated in reference to its maximal activity, the two enabling similar neuromuscular responses. On the other hand, it was evidenced that iMVC and pedalling movement di.er signi.cantly in biomechanical function and regulation of the lower limb muscles activation(Rouf­
fet and Hautier, 2007).
Another interesting similarity between MIP and the cycling action is the angular velocity pro.le of the crank. It has been previously demonstrated that the instantaneous crank angular velocity is not constant throughout the ped­alling action, rather, it is dependent on the angles of the lower limb relative to the crank position. In fact, the high­est and lowest angular velocities occur when the cranks are near vertical and horizontal, respectively(Moussay et al., 2003). This pattern was evident during MIP, despite the isokinetic modality. This is due to the fact that the accom­modating braking power exerted by the ergometer is reduced to near zero when the cranks are in vertical posi­tion and increased when the cranks are in horizontal posi­tion, in order to maintain the desired rotational speed (Wooles, 2006). Actually, this mechanism does not seem to be able to keep completely steady the instantaneous angular velocity of the crank, at least when the cyclist is asked to pedal at 80 rpm and maximal intensity.
From the issues above discussed it could be maintained that the procedure employed in the current setting is highly speci.c to the cycling gesture. Furthermore, using the cur­rent procedures, each muscle may be assessed at the same time, this being a time-and energy-saving process. In con­trast, an isometric contraction would entail a more compli­cated procedure, especially when several muscles require to be analysed, namely an iMVC has to be produced sepa­rately for every single muscle involved in the action(Hsu et al., 2006; Rou.et and Hautier, 2007).
A common problem of iMVCis thata certain degree of familiarization is required during the normalization session. Auseful implication from the data presented is that cyclists do not need to get skilled with the MIP, since no learning e.ect was demonstrated during the trials(Fig.3). Indeed, both PO and EMG activity reached their maximal values respectively, on average, on the 4th and within the 3rd trial. Although the PO and EMG maximal values are not attained at the same trial, it is important to underline that the variability among trials is negligible. Indeed, the average di.erence between the best and the worst value in the .rst .ve trials is 2% for PO and from 3% (BF) to 7% (GL) for the EMG of the four analysed muscles. As a result, based on the data collected, three trials of the MIP proposed appeartobe su.cient for the purposeof EMG normaliza­tion in cycling. Thus, the important goal of time e.ciency during testing sessions is also achieved.
As recently pointed out, the repeatability of EMG recorded during dynamic exercise, especially the muscles involved in a cycling action, has not been fully established (Laplaud et al., 2006). A strong point of the method pro­posed is the high degree of reliability. EMG signal of the VL, compared to the other muscles analysed, showed the lowest variability and this is in agreement with previous studies which found the EMG activity of VL during cycling to have a high reproducibility (Ryan and Gregor, 1992; Taylor and Bronks, 1995). When comparing the activity of the same muscles, the CVs are considerably lower than those presented by Rou.et and Hautier (2007) who used a maximal torque–velocity test, although it is important to mention that the subjects oftheir study were not cyclists.

4.1. Limitations
The protocols proposed were performed at 80 rpm. This cadence is widely used in cycling related researches(Baum and Li, 2003; Hull and Jorge, 1985); furthermore, previous studies found that freely chosen cadence in cyclists ranges between78 and 91 rpm(Foss and Halle´n, 2005; Hagberg et al., 1981; Nielsen et al., 2004). Notwithstanding, a cadence of 100–115 rpm, rather than 80 rpm, makes the cyclist attain the maximal power output (Baron, 2001; Baron et al., 1999; Sargeant et al., 1981). Consequently, the pedalling frequency chosen in the present study is situ­ated in the ascending part of the power–cadence curve. Takaishi et al. (1998) demonstrated that the EMG/cadence curve at constant power and pedalling frequency ranging from 45 to 105 rpm showed a quadratic trend. The mini­mum EMG value was registered at 60 rpm, afterward it exhibited an increase as a function of cadence. It is there­fore expected that maximal isokinetic pedalling at higher cadences would lead to higher EMG values, although this issue needs to be investigated further on.
As a consequence, the reference contraction here pro­posed at 80 rpm should be used only for submaximal bicy­cling exercises performed at the same cadence. In general terms it could be argued that, whatever the pedalling rate chosen for SMP, the MIP should be performed at the same cadence.
5. Conclusion
The new protocol proposed for the purpose of EMG normalization in cycling, which consists of three 6-s maxi­mal isokinentic pedalling sprints, has very good logical validity and within-subject reproducibility. Further, the test is also highly speci.c to the actions associated with cycling. The chosen cadence of the normalization protocol should be the same as the sub-maximal exercises.
Acknowledgements
The authors wouldlike to thankAPLab engineers, espe­cially Nunzio Lanotte, who have designed the data acqui­sition system, for their technical assistance; Mark Watsford, Ph.D., lecturer in Exercise and Sports Science School of Leisure, Sport and Tourism University of Tech­nology (Sydney) and Francesco Felici, M.D., professor of exercise physiology, Istituto UniversitariodiScienzeMoto­rie (Rome) for their assistance and suggestions in revising the paper.

References
Arokoski JP, Kankaanpaa M, Valta T, Juvonen I, Partanen J, Taimela S, et al. Back and hip extensor muscle function during therapeutic exercises. Arch Phys Med Rehabil 1999;80:842–50.
Baron R. Aerobic and anaerobic power characteristics of o.-road cyclists. Med Sci Sports Exerc 2001;33:1387–93.
Baron R, Bachl N, Petschnig R, Tschan H, Smekal G, Pokan R. Measurement of maximal power output in isokinetic and non­isokinetic cycling. A comparison of two methods. Int J Sports Med 1999;20:532–7.
Baum BS, Li L. Lower extremity muscle activities during cycling are in.uenced by load and frequency. J Electromyogr Kinesiol 2003;13:181–90.
Bolgla LA, Uhl TL. Reliability of electromyographic normalization methods for evaluating the hip musculature. J Electromyogr Kinesiol 2007;17:102–11.
Clarys JP, Cabri J. Electromyography and the study of sports movements: a review. J Sports Sci 1993;11:379–448.
Dankaerts W, O’Sullivan PB, Burnett AF, Straker LM, Danneels LA. Reliability of EMG measurements for trunk muscles during maximal and sub-maximal voluntary isometric contractions in healthy controls and CLBP patients. J Electromyogr Kinesiol 2004;14:333–42.
Dano. JV. EMG normalization. Phys Ther 1986;66:270–2.
Enoka RM, Fuglevand AJ. Neuromuscular basis of the maximum voluntary force capacity of muscle. In: Grabiner MD, editor. Current issues in biomechanics. Champaign, IL: Human Kinetics; 1993. p. 215–35.
Ericson M. On the biomechanics of cycling. A study of joint and muscle load during exercise on the bicycle ergometer. Scand J Rehabil Med Suppl 1986;16:1–43.
Ericson MO, Nisell R, Arborelius UP, Ekholm J. Muscular activity during ergometer cycling. Scand J Rehabil Med 1985;17:53–61.
Foss Ø, Halle´n J. Cadence and performance in elite cyclists. Eur J Appl Physiol 2005;93:453–62.
FreriksB, HermensH, Disselhorst-KlugC,RauG.The recommendations for sensors and sensor placement procedures for surface electromyog­raphy. In: Hermens H, Freriks B, Merletti R, Stegeman D, Blok J, Rau G, et al., editors. European recommendations for surface electromy­ography. Enschede (The Netherlands): Roessingh Research and Development BV; 1999. p. 15–54.
Hagberg JM, Mullin JP, Giese MD, Spitznagel E. E.ect of pedaling rate on submaximal exercise responses of competitive cyclists. J Appl Physiol 1981;51:447–51.
Hautier CA, Arsac LM, Deghdegh K, Souquet J, Belli A, Lacour JR. In.uence of fatigue on EMG/force ratio and cocontraction in cycling. Med Sci Sports Exerc 2000;32:839–43.
Hopkins WG. A new view of statistics. Available from: http://sport­
sci.org/resource/stats [Accessed 2007 Feb 27].
Hopkins WG.Measures of reliability in sports medicine and science. Sport Med 2000;30:1–15.
Hsu WL, Krishnamoorthy V, Scholz JP. An alternative test of electro­myographic normalization in patients. Muscle Nerve 2006;33:232–41.
Hug F, Bendahan D, Le Fur Y, Cozzone PJ, Grelot L. Heterogeneity of muscle recruitment pattern during pedaling in professional road cyclists: a magnetic resonance imaging and electromyography study. Eur J Appl Physiol 2004a;92:334–42.
Hug F, Decherchi P, Marqueste T, Jammes Y. EMG versus oxygen uptake during cycling exercise in trained and untrained subjects. J Electromyogr Kinesiol 2004b;14:187–95.
Hull ML, Jorge M. A method for biomechanical analysis of bicycle pedalling. J Biomech 1985;18:631–44.
Hunt MA, Sanderson DJ, Mo.et H, Inglis JT. Biomechanical changes elicited by an anterior cruciate ligament de.ciency during steady rate cycling. Clin Biomech 2003;18:393–400.
Hunter AM, St Clair Gibson A, Lambert M, Noakes TD. Electromyo­graphic (EMG) normalization method for cycle fatigue protocols. Med Sci Sports Exerc 2002;34:857–61.
Kollmitzer J, Ebenbichler GR, Kopf A. Reliability of surface electro­myographic measurements. Clin Neurophysiol 1999;110:725–34.
Laplaud D, Hug F, Grelot L. Reproducibility of eight lower limb muscles activity level in the course of an incremental pedaling exercise. J Electromyogr Kinesiol 2006;16:158–66.
Latash ML. Neurophysiological basis of movement. 1st ed. Champaign, IL: Human Kinetics; 1998.
Lehman GJ, McGill SM. The importance of normalization in the interpretation of surface electromyography: a proof of principle. J Manipulative Physiol Ther 1999;22:444–6.
Lobbezoo F, van der Glas HW, Buchner R, van der Bilt A, Bosman F. Gain and threshold of the jaw-jerk re.ex in man during isometric contraction. Exp Brain Res 1993;93:129–38.
Marras WS, Davis KG. A non-MVC EMG normalization technique for the trunk musculature: Part 1. Method development. J Electromyogr Kinesiol 2001;11:1–9.
Marsh AP, Martin PE. The relationship between cadence and lower extremity EMG in cyclists and noncyclists. Med Sci Sports Exerc 1995;27:217–25.
Mirka GA. The quanti.cationofEMG normalization error. Ergonomics 1991;34:343–52.
Moussay S, Bessot N, Gauthier A, Larue J, Sesboue B, Davenne D. Diurnal variations in cycling kinematics. Chronobiol Int 2003;20:879–92.
Neptune RR, Herzog W. Adaptation of muscle coordination to altered task mechanics during steady-state cycling. J Biomech 2000;33: 165–72.
Neptune RR, Kautz SA, Hull ML. The e.ect of pedaling rate on coordination in cycling. J Biomech 1997;30:1051–8.
Nielsen JS, Hansen EA, Sjogaard G. Pedalling rate a.ects endurance performance during high-intensity cycling. Eur J Appl Physiol 2004;92:114–20.
Prilutsky BI, Gregor RJ, Ryan MM. Coordination of two-joint rectus femoris and hamstrings during the swing phase of human walking and running. Exp Brain Res 1998;120:479–86.
Rou.et DM, Hautier CA. EMG normalization to study muscle activa­tion in cycling. J Electromyogr Kinesiol 2007. doi:10.1016/ j.jelekin.2007.03.008.
Ryan MM, Gregor RJ. EMG pro.les of lower extremity muscles during cycling at constant workload and cadence. J. Electromyogr. Kinesiol. 1992;2:69–80.
Sargeant AJ, Hoinville E, Young A. Maximum leg force and power output during short-term dynamic exercise. J Appl Physiol 1981;51:1175–82.
Smith J, Padgett DJ, Dahm DL, Kaufman KR, Harrington SP, Morrow DA, et al. Electromyographic activity in the immobilized shoulder girdle musculature during contralateral upper limb movements. J Shoulder Elbow Surg 2004;13:583–8.
Soderberg GL, Knutson LM. A guide for use and interpretation of kinesiologic electromyographic data. Phys Ther 2000;80:485–98.
Takaishi T, Yamamoto T, Ono T, Ito T, Moritani T. Neuromuscular, metabolic, and kinetic adaptations for skilled pedaling performancein cyclists. Med Sci Sports Exerc 1998;30:442–9.
Taylor AD, Bronks R. Reproducibility and validity of the quadriceps muscle integrated electromyogram threshold during incremental cycle ergometry. Eur J Appl Physiol Occup Physiol 1995;70:252–7.
van Diee¨n JH, Selen LP, Cholewicki J. Trunk muscle activation in low-back pain patients, an analysis of the literature. J Electromyogr Kinesiol 2003;13:333–51.
Wooles A. SRM user manual. 4th ed. Schoberer Rad Meßtechnik; 2006.

E. Ferna´ ndez-Pen˜a et al./Journal of Electromyography and Kinesiology xxx (2008) xxx–xxx 9

Eneko Ferna´ndez Pen˜a received his degree in Physical Education from the Basque Institute of Physical Education (SHEE/IVEF, Vitoria-Gasteiz, Spain) in July 2003, and his Ph.D. degree from the University of Urbino ‘‘Carlo Bo” (Italy) in March 2007. He is currently a post-doctoral fellow at the Institute of Health and Physical Exercise (Urbino, Italy), and his research interest focuses on biomechanics of cycling.
Francesco Lucertini received his diploma in Physical Education (1998) and his degree in Exercise Sciences (2001) from University of Urbino ‘‘Carlo Bo” (Italy). He received the Ph.D. degree in February 2006 from the Fac­ulty of Health and Sport Sciences of the same University and he is currently a post-doctoral fellow at the Institute of Health and Physical Exercise (Urbino, Italy). His research interest focuses on performance assessment in both sport-and health-related topics.

Massimiliano Ditroilo has a diploma in Physical Education (1992), a degree in Biological Sci­ences (1999) and a master degree in Methods of Training (2001). He is currently working within the Institute of Health and Physical Exercise at Urbino University (Italy). His research focuses on biomechanics and performance assessment of cycling, athletics, swimming and team sports.

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