F. Di Nardo

EMG-Based Analysis of Treadmill and Ground Walking in Distal Leg Muscles

Differences between treadmill and ground walking have been suspected by some authors. To check this hypothesis, the present study compared treadmill with ground walking in terms of surface electromyographic (sEMG) signal of Tibialis Anterioris (TA) and Gastrocnemius Lateralis (GL), from a large number (hundreds) of strides per subject. The analysis on seven healthy young adults showed no substantial variation in TA activity during treadmill walking, with respect to ground walking. An earlier and increased activity of GL during the transition between Flat foot contact and Push-off phases was detected during treadmill walking with respect to ground walking in terms of both the frequency of GL recruitment and area under the curve of GL profiles; this increase is likely to be related with the reported increase of magnitude of vertical forces during mid-stance in the treadmill compared with ground walking. Incorporating this findings into gaitanalysis strategies could lead to a more accurate evaluation of results achieved by the use of treadmill.

Statistical Analysis of EMG Signal Acquired from Tibialis Anterior during Gait

Aim of the present study was to identify the different modalities of activation of tibialis anterior (TA) during gait at self-selected speed, by a statistical analysis of surface electromyographic signal from a large number (hundreds) of strides per subject. The analysis on ten healthy adults showed that TA is characterized by different activation modalities within different strides of the same walk. The most recurrent modality consists of three activations observed in 37.4±1.9% of total strides: at the beginning of gait cycle, around stance-to swing-transition and in the terminal swing. Further two modalities differ from the most recurrent one because of 1) the continuous activation during swing; 2) a further activity in the late mid-stance. The study of these different modalities of activation suggested that TA acts as pure ankle dorsi-flexor only in a small percentage ( 20%) of total strides, where TA activity occurs in the simpler modality. The increase in the complexity of the recruitment of the muscle introduces an uncommon activity during mid-stance, which does not occur for the flexion of the ankle but is related to the activity of the TA as a foot invertor muscle.

Evaluation of gender-related differences in co-contraction activity of shank muscles during gait

This study aims to investigate the possible differences between genders in co-contractions of tibialis anterior (TA) and gastrocnemius lateralis (GL), during walking at self-selected speed. To this purpose, the statistical gait analysis (SGA) was performed on seven female (F-group) and seven male (M-group) adults. SGA is a recently developed methodology for the characterization of gait, by averaging spatiotemporal and electromyographic parameters over hundreds of strides per subject. Co-contractions were assessed as the overlapping periods between TA and GL activity. Results showed that four co-contraction intervals are present during gait cycle in both groups. No relevant differences between genders were detected in onset-offset time instants of co-activations or in their temporal length. On the contrary, significant differences were observed in the number of strides where each co-contraction happens (i.e. the occurrence frequency). All the four co-contraction intervals result significantly (p<;0.05) more recurrent in females compared to males. This outcome suggests a larger presence of co-contraction activity in females walking, related to a female tendency for a more complex muscular strategy during gait. These findings could be useful to better understand gender differences in walking mechanisms and to develop separated normal walking reference frames for males and females.

Influence of gender on the myoelectric signal of shank muscles

The surface electromyographic (sEMG) signal is commonly utilized as principal input information to the controller of robotic systems, such as exoskeleton robots. It has been shown that sEMG signals could vary from subject to subject, and that gender is one of the factors influencing this variation. Thus, the goal of this study is to detect possible gender-related differences in the EMG activity of the two main ankle-flexor muscles (tibialis anterior, TA and gastrocnemius lateralis, GL) during gait at comfortable speed and cadence. The statistical analysis of surface EMG signals, performed in seven male (M-group) and seven female (F-group) age-matched adults, showed clear gender-related differences in the behavior of TA and GL. The estimation of the different activation modalities, indeed, permitted to detect that F-group choose a walking modality with a more elevated number of activations during gait cycle, compared to M-group. This suggests a propensity of females for a more complex recruitment of the muscles during gait. The novel information on gender-related differences provided here suggest considering a separate approach for males and females, in providing electromyographic signals as input information to the controller of exoskeleton robot.

The segmented-beat modulation method for ECG estimation.

Electrocardiographic (ECG) tracings corrupted by noise with frequency components in the ECG frequency band, may result useless unless appropriately processed. The estimation of the clean ECG from such recordings, however, is quite challenging; being linear filtering inappropriate. In the common situations in which the R peaks are detectable, template-based techniques have been proposed to estimate the ECG by a template-beat concatenation. However, such techniques have the major limit of not being able to reproduce physiological heart-rate and morphological variability. Thus, the aim of the present study was to propose the segmented-beat modulation method (SBMM) as the technique that overcomes such limit. The SBMM is an improved template-based technique that provides good-quality estimations of ECG tracings characterized by some heart-rate and morphological variability. It segments the template ECG beat into QRS and TUP segments and then, before concatenation, it applies a modulation/demodulation process to the TUP-segment so that the estimated-beat duration and morphology adjust to those of the corresponding original-beat. To test its performance, the SBMM was applied to 19 ECG tracings from normal subjects. There were no errors in estimating the R peak location, and the errors in the QRS and TUP segments were low (≤65 μV and ≤30 μV, respectively), with the former ones being significantly higher than the latter ones. Eventually, TUP errors tended to increase with increasing heart-rate variability (correlation coefficient: 0.59, P<;10-2). In conclusion, the new SBMM proved to be a useful tool for providing good-quality ECG estimations of tracings characterized by heart-rate and morphological variability.

Glucose absorption and insulin sensitivity from oral glucose tolerance test

Aim of the study was to develop a new glucose minimal model for evaluation of insulin sensitivity, S/sub I/, from an oral glucose tolerance test (OGTT). This model was obtained by coupling the minimal model of glucose kinetics with a monocompartmental model of the gut, which describes the relation between glucose ingested and glucose flux from the gut into plasma. Glucose rate of appearance into plasma, R/sub a/, is assumed to be linearly dependent on the glucose amount in the gut throughout a coefficient k/sub abs/, which represents the rate constant of glucose absorption from the gut. Application of our model to OGTT data from nine nondiabetic subjects showed its ability to provide precise estimates of both S/sub 1/ (7.04/spl plusmn/1.70 10/sup -4/ min/sup -1/ per /spl mu/U ml/sup -1/) and k/sub abs/ (2.89/spl plusmn/0.92 10/sup -2/ min/sup -1/). Thus, this new model appears a suitable tool to measure insulin sensitivity and the rate constant of glucose absorption during an oral test applicable in population studies.

A New Segmented-Beat Modulation Algorithm for Maternal ECG Estimation from Abdominal Recordings

The noninvasive fetal electrocardiogram (fECG) provides precious information about the physiological fetus state. It is extracted from abdominal recordings, obtained positioning surface electrodes on the maternal abdomen, by subtraction of the maternal ECG (mECG), often roughly estimated by simply concatenating a maternal-beat template. Aim of the present study is to propose a new algorithm for the mECG estimation based on a segmented-beat modulation method (SBMM) that adjusts the template length to the maternal physiological heart-rate variability (HRV) and reduces the level of noise. According to the SBMM, each maternal cardiac cycle (CC) is segmented into two segments, QRS and TUP, respectively independent and proportional to preceding RR interval. The estimated mECG is the concatenation of the template-beat, obtained as the median of the maternal beat after modulation and demodulation of TUP segment. The algorithm was applied to two (ARec1 and ARec2) 4-channel abdominal recordings obtained from pregnant women. ARec1 and ARec2 were both 60 s long and characterized by similar heart rate (HR: 80 bpm and 82 bpm) but different HRV (42 ms vs. 139 ms). Results indicate that the error in the mECG estimation is always small (<2.5 µV) but increases with HRV (ARec1: 0.87–1.65 µV; ARec2: 1.98–2.37 µV). In conclusion, the proposed algorithm based on the SBMM allows a clean mECG estimation from abdominal recordings thanks to a modulation procedure introduced to track physiological variation in the maternal heart rhythm.

A goniometer-based method for the assessment of gait parameters

Basic prerequisites for gait analysis are the assessment of spatio-temporal gait parameters and the analysis of movements within subsequent stride cycles. The aim of the present study is to propose a new method to assess spatio-temporal gait parameters using only 1-degree-of-freedom electrogoniometers positioned on hip and knee joints. The model validation is performed comparing the model results with those automatically obtained from another gait analysis system: GAITRite. The results underline the model reliability and show that the model could be a valid alternative to the traditional methods that use foot switches, ground reaction forces or accelerometers. These results show that essential spatio-temporal gait parameters can be determined during overground walking using only two 1-dof electrogoniometers. The method is easy-to-use and does not interfere with regular walking patterns.

Muscle activation patterns related to diabetic neuropathy in elderly subjects: A Functional Reach Test study

BACKGROUND This study was designed to assess, in healthy elderly, non-neuropathic and neuropathic diabetic subjects, the activation patterns of the main muscles involved in the Functional Reach Test, a well-recognized method to identify elderly subjects at risk of balance impairments. METHODS Surface electromyographic analysis of Sternocleidomastoideus, Rectus Abdominis, Erectores Spinae at L4 level, Rectus Femoris, Hamstrings, Tibialis Anterior and Soleus was performed in 10 healthy, 10 diabetic non-neuropathic and 10 diabetic neuropathic subjects. FINDINGS Results showed that in every group the first motor is Tibialis Anterior, that is recruited before the start of the test. An earlier activation of Tibialis Anterior (P<0.05) was detected in diabetic neuropathic (ON at -24% of the test period), compared with healthy (-11%) and diabetic non-neuropathic (-13%) groups. A significant earlier activation of Sternocleidomastoideus and Rectus Abdominis was found in diabetic neuropathic group, only with respect to healthy subjects. No significant difference was found in Rectus Femoris, Soleus, Hamstrings an Erectores Spinae onset among the three groups. INTERPRETATION Results suggest a trend of diabetic neuropathic patients in earlier anticipation of the activation of the anterior body-muscles. In particular, the earlier onset of Tibialis Anterior is likely to be performed to adjust the movement timing and to compensate for the delay in the recruitment of the motor units. This anticipation might be involved in the altered postural control with increased balance impairment detected in diabetic neuropathic patients, and thereby it might also be proposed as an index of neuropathy, evidenced in a simple and non-invasive manner.

The surface electromyographic evaluation of the Functional Reach in elderly subjects

This study proposes a comprehensive assessment of myoelectric activity of the main muscles involved in the Functional Reach (FR) test, in 24 elderly subjects. A specific protocol for the surface electromyography (sEMG) signal acquisition during FR-test was developed. Results show that anterior muscles activate following a caudo-cranial order. Tibialis Anterior (TA) is the first to be activated (-18.0±16.3% of the FR-period), together with Rectus Femoris (-10.4±17.9%). Then, Rectus Abdominis (19.7±24.7%) and Sternocleidomastoideus (19.9±15.6%) activate after the FR-start. Hamstrings, Soleus, and L4-level Erectores Spinae (posterior muscles) activate after the FR-start in this order (11.4±16.8%, 17.7±16.6%, and 35.2±29.0%, respectively) and remain active until the movement end. The analysis of the kinematic strategies adopted by subjects revealed an association between TA-activation patterns and two kinematic strategies (hip/mixed strategy), quantified by an increase (p<0.05) of TA-activity duration in subjects adopting the hip strategy (89.9±34.5) vs. subjects adopting the mixed strategy (27.0±16.8). This suggests that TA sEMG activity could be able to discriminate among kinematic strategies, providing different information on balance control. Thus, the present analysis represents the first attempt to quantify the sEMG activity during FR-test in elderly subjects, providing an early contribution in building a reference frame for balance assessment in clinical context.