ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

predicted. This is possible for models with more DOF, depending on the directions of
the moments in the joints, and if biarticular muscles are properly modeled [3]. If
however, there are no biarticular muscles or each of them is supposed to develop
moment only in one joint, the optimization task can be separated into several tasks (as
many as the degrees of freedom or number of moment equations are) which are typical
for one DOF models and the problem with suitable prediction of muscle synergism and
antagonistic co-contraction remains. These modeling problems are more evident for
fast, dynamic motions, where two or three phases of muscle activities are
experimentally demonstrated.
There are well known obstacles concerning processing of experimental surface
EMG signals and their comparison with predicted by models muscle forces [4]. The
EMG signals give a general impression about the electrical pulses received by MUs.
Each pulse, however, results in different mechanical output and this output is also very
different for each particular MU [5, 6]. For example, slow MUs have low force level
and long force duration, fast MUs are much stronger, but their forces are shorter in time.
That is why a direct relationship "force-EMGs" is very hard to be obtained in a general
form for all type of movements. One alternative for verification of the models is not to
relate experimental EMGs with muscle force but with other model outputs, like
excitation signals or simulated EMGs [7], which outputs are similar in nature to EMGs.
The aim of the paper is to investigate experimentally (by recording and
processing EMG signals from the muscles biceps brachii and triceps brachii and elbow
angle) and by means of modelling (using MotCo software) elbow flexion/extension
movements (full flexion) in the sagittal plane with different, controlled, speeds - from
very slow to maximally fast.
3. EXPERIMENTAL PROCEDURE
Three healthy men participated in the experiments. The study was conducted in
accordance to the Declaration of Helsinki. The aim of the experiments was to perform
controlled maximal elbow flexion (from fully extended to fully flexed forearm) in the
sagittal plane with 6 different speeds and to return freely the hand in the initial position.
The angle of the right elbow joint was measured with twin axis goniometer (SG110,
Biometrics Ltd). The distal and the proximal end-blocks were attached using adhesive
tapes (Biometrics P.N. T10). The first one was aligned along the axis of the forearm and
the second one - along the axis of the upper arm. The central axis of rotation of the
goniometer was aligned in the midline of the lateral intra-articular space of the elbow
joint. Ag/AgCl electrodes were attached to the surface of the long head of the biceps
brachii muscle (BIC) and of the long head of the triceps brachii (TRI) muscle according
to the SENIAM recommendations. The distance between the centers of electrodes was
20 mm, while electrode diameter was 10 mm. Before attaching the electrodes, the skin
was shaved, rubbed with a sand paper, cleaned with an alcohol wipe and drayed. A
ground electrode was placed on the radial styloid process of the left forearm. With
attached electrodes all EMG channels were zeroed before pre-amplifying (SX230 pre-
amplifiers, Biometrics Ltd), filtered and stored on a computer disc using an analogue-todigital
13-bit converter at the sampling rate of 1 kHz (DataLINK DLK900, Biometrics
Ltd, UK). All experiments were performed in a sitting position with back support and
subjects were able to move their upper limbs with no limitations. Prior to the
experimental session subjects were instructed and practiced movements at six different
intended speeds (approximately 30, 60, 240, 360, 500 deg/s and a maximum voluntary
one). During testing each participant performed 5 repetitions of right elbow flexion at