Biomedical subjects

H M Toussaint

Publications and source records attributed to H M Toussaint.

At least 55 records · Page 3Linked to original sources

PubMed1993

Spinal shrinkage as a parameter of functional load.

This article reviews the possibilities of spinal shrinkage in ergonomic evaluation of working situations. Because long-term health effects due to spinal loading are difficult to assess, short-term effects of spinal loading, such as spinal shrinkage, are used to obtain insight in the workload and its consequences, based on an assumed predictive value regarding health effects. The mechanism underlying spinal shrinkage (i.e., loss of motion segment height) and its possible relationship to low back pain, the way in which spinal shrinkage has been measured in vivo, and some results of in vivo studies are discussed. Conclusions are drawn on the validity and applicability of spinal shrinkage in ergonomic evaluations. The validity needs further investigation in relation to the loads imposed on the spine, the capacity of the worker, and the health consequences.

Body Height↗

PubMed1993

Trunk extensor endurance and its relationship to electromyogram parameters.

The present study was designed to investigate the relationship between muscle performance and electromyogram (EMG) parameters of the trunk extensor muscles in the development of fatigue. Nine subjects performed continuous isometric trunk extensions at 25% and 40% maximal voluntary contraction. The EMG signals of the longissimus thoracis, iliocostalis lumborum, multifidus and latissimus dorsi muscles were recorded. The EMG amplitude (RA-EMG) appeared to increase consistently during the contractions in all muscles, whereas the mean power frequency (MPF) showed a fairly consistent decrease during the contractions. The time constants of the exponential change of the RA-EMG and of the MPF were related to the endurance time. The prediction of endurance based on both EMG parameters appeared to yield better results than the prediction based on the relative force. In particular the time constants of the MPF changes of the multifidus and longissimus muscles appeared to be good predictors of endurance time. The consistency of the spectrum shift of EMG appeared to coincide with a reduced variability of the activation of the muscle involved.

Adult↗

PubMed1993

An investigation into the relevance of the pattern of temporal activation with respect to erector spinae muscle endurance.

The aim of the present study was to evaluate the viability of a relationship between the temporal activation pattern of parts of the erector spinae muscle and endurance. Seven subjects performed intermittent isometric contractions [4s at 70% maximal voluntary contraction (MVC), 2 s rest] until exhaustion, during which the electromyographical (EMG) activity of the multifidus, iliocostalis thoracis and longissimus muscle segments was recorded. Endurance was defined as the time until exhaustion. Subjects were divided into a high and a low endurance group. The high endurance group showed significantly more variability of EMG amplitude over succeeding contractions. This group demonstrated significantly more alternations of EMG activity between parts of the muscle also. Variability of the EMG amplitude within the contractions did not differ between the groups, nor did MVC. The results indicated that alternating activity between different parts of the erector spinae muscle may function to postpone exhaustion of this muscle as a whole.

Adult↗

PubMed1993

Recommendations for the assessment and design of young children's bicycles on the basis of anthropometric data.

Children's bicycles are the product most often involved in leisure accidents to children. One of the possible reasons for this might be a lack of fit between the dimensions of the bicycle and the dimensions of the child. In a project entitled KIMA-1, some 33 dimensions of 279 children (aged 2.5-5.5 years) were measured at seven infant welfare centres in the province of Zuid, Holland. These data were used to compare dimensions of children with dimensions of bicycles. Furthermore, the requirements regarding bicycle dimensions laid down in product safety acts of different countries were compared with both the results of KIMA-1 and some bicycles available in shops. It is concluded that maximum product safety and comfort of the bicycle are achieved when the bicycle is fitted to the dimensions of the child. Enhancement of this fitting process can be achieved by relating the dimensions of the bicycle to the stature rather than to the age of the child. The comparison of the KIMA-1 data to the dimensions laid down in product safety acts led to the conclusion that Dutch children are larger than the population on which the safety dimensions are based. Furthermore, secular changes in body dimensions call for a revision of the relevant safety dimensions in 10-15 years.

Journal Article↗

PubMed1993

Joint moments and muscle activity in the lower extremities and lower back in lifting and lowering tasks.

The mechanical loading on the body during the act of lifting has been estimated frequently. The opposite act of lowering has received much less attention. The aim of the present study was to compare the mechanical loading of the musculoskeletal system in lifting and lowering. Eight subjects repetitively lifted and lowered a load, using two different techniques (a leg and a back technique). The ankle, knee, hip and lumbosacral joint moments were estimated and the myoelectrical (EMG) activity of seven (leg and back) muscles was recorded. The differences between the lifting and lowering phase for the leg technique were similar to those observed when the back technique was applied. The joint moment curves in lifting showed a high level of agreement with the (time-reversed) moment curves in lowering. Peak moments in lowering were only slightly lower than in lifting (peak lumbar moments were 5.4% lower). These small differences were related to different acceleration profiles at the centre of gravity of the body/load complex. The EMG activity was considerably lower in lowering than in lifting. The mean EMG in lowering (average for seven muscles) was only about 69% of the EMG in lifting. This was attributed to the different types of muscle actions involved in lifting (mainly concentric) and lowering (mainly eccentric). Furthermore, the EMG results suggest that similar inter-muscular coordination is involved in lowering and lifting. The results give rise to the assumption that in lifting and lowering similar muscle forces are produced to meet the (nearly) equal joint moments, but in lowering these forces are distributed over a smaller cross-sectional area of active muscle, which might imply a higher risk of injury.

Acceleration↗

PubMed1993

Spectral analysis of erector spinae EMG during intermittent isometric fatiguing exercise.

The applicability of EMG spectral analysis in the study of muscular fatigue of the erector spinae muscle was investigated. At three locations (L1, L2, L5) of the erector spinae muscle, representing different functional parts, EMG was sampled during fatiguing intermittent isometric extension of the trunk. The multifidus muscle (L5) appeared to show the most consistent changes of the EMG power spectrum as a consequence of fatigue. Whether the effects of the increase in muscle temperature on the power spectrum could be eliminated by low-pass filtering the data (60 Hz and 40 Hz) was also investigated. It was expected that this would make it possible to detect better the effects of fatigue on the firing characteristics of the motorunits by the inherent changes in the power spectrum. Low-pass filtering did not cause a more significant trend of the median frequency of the power spectrum. Future research will have to explore which parts of the power spectrum are affected by an increase of the muscle temperature.

Adult↗

PubMed1992

Effects on efficiency in repetitive lifting of load and frequency combinations at a constant total power output.

Boxes were lifted and lowered repetitively at three different combinations of load and frequency. These combinations were chosen such that the total mechanical power generated was constant. Effects of the varying load or frequency conditions (but constant total mechanical power) on the rate of energy expenditure (M) and on the mechanical efficiency (ME) were measured. Mechanical power was determined from film analysis and separated into external power (generated to lift the load) and internal power (to raise the lifter's body mass). The M was determined from oxygen consumption measurements. The ME was calculated in two ways, depending on the definition of mechanical power, including either the external power only (MEext) or the total power output (MEtot). Despite a constant total mechanical power, M increased at higher loads and lower frequencies. This might be explained by the increasing isometric force required in postural and load control. The M increase resulted in a decrease of MEtot. However, at higher loads and lower frequencies MEext increased, indicating that more external work can be done at the same energy costs at higher loads or lower frequencies, which could be of interest from the point of view of occupational physiology. It would seem that at higher loads or lower frequencies the increased costs for isometric muscle action do not outweigh the benefit of raising the body less frequently. Furthermore, it was found that the MEext in lifting was much lower than the values reported for other kinds of activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Different methods to estimate total power and its components during lifting.

A more fundamental understanding about the act of manual lifting can be provided by the assessment of the total production of power and the power generated in joints. The present study is concerned with the validity of the estimations of these parameters. Four subjects lifted an 18.8 kg load while they were filmed and ground reaction forces were measured. The total generated power was calculated in three ways: (1) by summation of joint powers, (2) on the basis of the rate of change of the summed energy contents of human body segments, and (3) on the basis of the rate of change of the body energy estimated from ground reaction forces. The results were compared. Furthermore, at a segmental level the power supplied to or absorbed from a segment was compared to the rate of change of its energy content. The resulting instantaneous power curves from the three different methods showed a high level of agreement, which supports their validity. However, some minor discrepancies were observed. The major cause of the observed difference between the rate of change of the summed segmental energy contents and the summed joint powers was found at a segmental level. It was observed that segmental link lengths (i.e. distances between proximal and distal markers) changed during movement, which yielded discrepancies between the power flow to or from a segment and the rate of change of its energy content.

Adult↗

PubMed1992

Coordination of the leg muscles in backlift and leglift.

Net joint moments are often used to quantify the loading of structures (e.g. the intervertebral disc at L5S1) during lifting. This quantification method is also used to evaluate the loading of the knee, for instance, to determine the effect of backlifting as opposed to leglifting. However, the true loading of the joint as derived from net joint moments can be obscured by a possible co-contraction of antagonists. To unravel the mechanisms that determine the net joint moments in the knee, the leglift was compared to the backlift. Although a completely different net knee moment curve was found when comparing the two lifting techniques, it appeared to be closely related to the ground reaction force vector and its orientation with respect to the joint centre of rotation (R > 0.995). This close relation was established by co-contraction of both flexors and extensors of the knee. Furthermore, a close relation appeared to exist between the joint moment difference between hip and knee and the activity difference between rectus femoris muscle and hamstring (R = 0.72 and 0.83 in leglift and backlift, respectively). The knee-ankle joint moment difference and the activity of the gastrocnemius showed a close relation as well (R = -0.89 and 0.96 in leglift and backlift, respectively). These relations can be interpreted as a mechanism to distribute net moments across joints. It is concluded that during lifting tasks the intermuscular coordination is aimed at coupling of joint moments, such that the ground reaction force points in a direction that provides balance during the movement. The use of net joint moments as direct indicators for joint loading (e.g. knee) seems, therefore, questionable.

Adult↗

PubMed1992

Biomechanics of competitive front crawl swimming.

Essential performance-determining factors in front crawl swimming can be analysed within a biomechanical framework, in reference to the physiological basis of performance. These factors include: active drag forces, effective propulsive forces, propelling efficiency and power output. The success of a swimmer is determined by the ability to generate propulsive force, while reducing the resistance to forward motion. Although for a given competitive stroke a range of optimal stroking styles may be expected across a sample of swimmers, a common element of technique related to a high performance level is the use of complex sculling motions of the hands to generate especially lift forces. By changing the orientation of the hand the propulsive force acting on the hand is aimed successfully in the direction of motion. Furthermore, the swimming velocity (v) is related to drag (A), power input (Pi, the rate of energy liberation via the aerobic/anaerobic metabolism), the gross efficiency (eg), propelling efficiency (ep), and power output (Po) according to: [formula; see text] Based on the research available at present it is concluded that: (a) drag in groups of elite swimmers homogeneous with respect to swimming technique is determined by anthropometric dimensions; (b) total mechanical power output (Po) is important since improvement in performance is related to increased Po. Furthermore, it shows dramatic changes with training and possibly reflects the size of the 'swimming engine'; (c) propelling efficiency seems to be important since it is much higher in elite swimmers (61%) than in triathletes (44%); and (d) distance per stroke gives a fairly good indication of propelling efficiency and may be used to evaluate individual progress in technical ability.

Arm↗

PubMed1991

The electro-mechanical delay of the erector spinae muscle: influence of rate of force development, fatigue and electrode location.

Electro-mechanical delay (EMD) values of the erector spinae muscle were obtained using a technique based on the cross-correlation between the force and the electromyogram (EMG). Seven subjects performed a series of 20 submaximal dynamic isometric contractions in a seated position at two frequencies (0.5 Hz and 1 Hz) to study the influence of the rate of force development on EMD. Mean EMD values of 125.7 (SD 28.1) ms (1 Hz) and 136.8 (SD 28.6) ms (0.5 Hz) were shown to differ significantly (P = 0.02). This finding supports the hypothesis that EMD is inversely related to the rate of force development and implies that the time to stretch the series elastic component is an important factor determining EMD. After performing a series of fatiguing contractions EMD did not differ significantly from the control value. Multiple regression analysis showed that maximal voluntary contraction force (MVC) and endurance time of the fatiguing exercise correlated significantly with EMD. The site from which the EMG signal was recorded had no significant influence on EMD. However, the coefficient of correlation between force and the EMG-signal differed significantly between electrode positions. The magnitude of the EMD values found emphasized the need to account for this delay when interpreting temporal patterns of activation of the muscles in, for example, lifting tasks.

Adult↗

PubMed1991

Effect of propelling surface size on the mechanics and energetics of front crawl swimming.

In swimming the propulsive force is generated by giving a velocity change to masses of water. In this process energy is transferred from the swimmer to the water, which cannot be used to propel the swimmer. Theoretical considerations indicated that an increase of the propelling surface size should lead to a reduced loss of energy to the water. Thus, in this study, the effect of artificially enlarging the propelling surface of the hand was examined. The effect was examined in terms of the propelling efficiency during front crawl swimming using the arms alone. The legs were floated with a small buoy as previously described (Toussaint et al., J. appl. Physiol. 65, 2506-2512, 1988a). In ten competitive swimmers (six male, four female) the rate of energy expenditure (power input, Pi), power output (Po), work per stroke cycle (As), distance per stroke cycle (d), work per unit distance (Ad), and propelling efficiency (ep) were determined at various swimming speeds once with and once swimming without paddles. At the same average velocity the effect of swimming with paddles was to reduce Pi, Po, and Ad by 6, 7.6, and 7.5% respectively, but to increase ep and As by 7.8 and 7%. The increase in distance per stroke cycle and the decrease in stroke cycle frequency matched the predicted values based on the theoretical considerations in which the actual increase in propelling surface size was taken into account.

Arm↗

PubMed1991

Efficiency and effectiveness of stoop and squat lifting at different frequencies.

The study investigated the effects of frequency (10 and 20 lifts/min) and technique (squat and stoop) of repetitive lifting of a barbell (19 kg) on the relationship between mean power output (Pm) and energy cost in 9 male power-lifters. Oxygen uptake (VO2) was measured directly and continuously and power output was deduced from film analysis using an inverse dynamic analysis. Power output and VO2 were significantly greater for squat than for stoop lifting at the same frequency. The mechanical efficiency (ME), defined as Pm divided by the energy equivalence of VO2, increased from 12% at rate 10 to 18.5% at rate 20, but there was no significant difference between the two techniques. The effectiveness (EF), defined as the productive external power output (only work done on the barbell) divided by the energy equivalence of VO2, was significantly higher for the stoop lift than for the squat lift. EF is judged as a more useful measure than ME for characterizing the relative energy cost of a lifting task.

Adolescent↗

PubMed1990

Effects of specific high resistance training in the water on competitive swimmers.

A new training device derived from the MAD-system (system to measure active drag, Hollander et al. (8], providing fixed push off points in the water for swimming, the front crawl is described. The effects of training on this device (called POP from fixed Push Off Point) are determined by comparing the increase in performance of a training group (n = 11) to a control group (n = 11). The control group continued the normal training program. During ten weeks the training group followed the same program, but three times per week sprints performed on the POP were substituted for normal free swimming sprints. Despite the fact that training time and volume were equal, the training group showed a significantly greater improvement in force (from 91 to 94 N, 3.3%), velocity (from 1.75 to 1.81 m.s-1, 3.4%) and power (from 160 to 172 W, 7%) as measured on the MAD-system, and an increase in distance per stroke in free swimming. The training group showed a significant improvement in race times for 50 m (from 27.2 to 26.6 s), 100 m (from 59.3 to 57.4 s) and 200 m (from 129.6 to 127.3 s). It is concluded that the POP is a specific training device especially suitable for increasing maximal power output during swimming.

Adolescent↗

PubMed1990

The mechanical efficiency of front crawl swimming.

In this study the gross efficiency of swimming was determined in a group of male (N = 6) and female (N = 4) competitive swimmers. The gross efficiency is defined as the ratio of the power output (W) to the power input (W). In a range of swimming velocities (0.95-1.6 m.s-1), the power input (rate of energy expenditure, 445-1137 W) was calculated from the oxygen uptake values (1.33-3.25 1 O2.min-1). The total power output (26-108 W) was directly measured during front crawl swimming using a system of underwater push-off pads instrumented with a force transducer (MAD-system). Using the MAD-system, the effect on total body drag due to the addition of the respiratory apparatus was evaluated to be negligible. The gross efficiency ranged from 5 to 9.5%. At equal swimming speed, the male competitive swimmers demonstrated a higher gross efficiency. However, this was due to the higher power output required by the male swimmers at a given speed. Gross efficiency was dependent on the absolute power output such that as power output increased so did the calculated gross efficiency. At the same power output, the values for the gross efficiency do not differ between the male and female competitive swimmers.

Biomechanical Phenomena↗

PubMed1990

Differences in propelling efficiency between competitive and triathlon swimmers.

Two highly trained groups, competitive swimmers (N = 6) and triathletes (N = 5), were compared to evaluate the significance of the propelling efficiency as a performance determining factor in swimming. Using regression equations, the groups were compared at equal power input (1000 W). The groups did not differ in gross efficiency, stroke frequency, and work per stroke. There was a difference in distance per stroke (1.23 m vs 0.92 m) and mean swimming velocity (1.17 m.s-1) vs 0.95 m.s-1). The difference in swimming speed between the two groups can be explained by the fact that the competitive swimmers used a much higher proportion of their power output to overcome drag (49 W vs 35 W). At the same time, the competitive swimmers expended less power in moving water backwards (32 W vs 45 W). This difference in apportionment of the power output was characterized as the propelling efficiency (power used to overcome drag/total power output). Mean (+/- SD) propelling efficiency for the competitive swimmers was 61 +/- 6% but was only 44 +/- 3% for the triathletes. The results suggest that on average the better swimmer distinguishes himself from the poorer one by a greater distance per stroke rather than a higher stroke frequency. It is concluded that triathletes should focus their attention on their swimming technique rather than their ability to do work. The distance per stroke might be a simple criterion to evaluate the improvement in skill.

Biomechanical Phenomena↗

PubMed1989

Effect of a triathlon wet suit on drag during swimming.

The effect of a triathlon wet suit on drag was studied in 12 subjects (eight male, four female) swimming at different velocities (1.10, 1.25 and 1.50 m.s-1). The active drag force was directly measured during front crawl swimming using a system of underwater push off pads instrumented with a force transducer (M.A.D. system: 6). Measurements were made when swimming over the system with and without a wet suit. A 14% reduction in drag (from 48.7 to 41.8 Newtons) is found at a swimming velocity of 1.25 m.s-1, which is a typical swimming speed for triathlon distances. At 1.50 m.s-1 a reduction in drag of 12% was observed, which suggests that the wearing of such a suit might be beneficial in conventional swimming events. The reduction in drag can explain the higher swimming velocities observed in triathletes using a wet suit. The effect of the reduction is probably largely due to an increased buoyancy inducing less frontal resistance. However, since the effect of the suit on the lighter female swimmers was not different from the effect on the heavier male swimmers, a reduction in friction drag and drag coefficient may also be significant.

Adult↗

PubMed1988

Active drag related to velocity in male and female swimmers.

Propulsive arm forces of 32 male and 9 female swimmers were measured during front crawl swimming using arms only, in a velocity range between 1.0 m s-1 and 1.8 m s-1. At constant velocity, the measured mean propulsive force Fp equals the mean active drag force (Fd). It was found that Fd is related to the swimming velocity v raised to the power 2.12 +/- 0.20 (males) or 2.28 +/- 0.35 (females). Although many subjects showed rather constant values of Fd/v2, 12 subjects gave significantly (p less than 0.01) stronger or weaker quadratic relationships. Differences in drag force and coefficient of drag between males and females (drag: 28.9 +/- 5.1 N, 20.4 +/- 1.9 N, drag coefficient: 0.64 +/- 0.09, 0.54 +/- 0.07 respectively) are especially apparent at the lowest swimming velocity (1 m s-1), which become less at higher swimming velocities. Possible explanations for the deviation of the power of the velocity from the ideal quadratic dependency are discussed.

Acceleration↗