Blood pressure and cardiovascular autonomic function in healthy children and adolescents.

OBJECTIVES: To investigate the relationship between blood pressure levels and cardiovascular autonomic function in adolescents and preadolescents. STUDY DESIGN: We measured variability of beat-to-beat arterial pressure and R-R intervals using power spectral analysis in 56 adolescents (aged 13-16 years; mean age, 9.0 +/- 1.4 years) and 71 preadolescents (6-12 years; mean age, 13.5 +/- 1.1 years) in the supine and standing positions. RESULTS: Adolescents had higher levels of systolic arterial pressure and lower high-frequency power of RR intervals than preadolescents. Correlation between the basal level of arterial pressure and autonomic function was observed in adolescents but not in preadolescents. In adolescents, multivariate analysis indicated that the basal level of arterial pressure was inversely related with the high-frequency power of RR intervals and positively with the ratio of low-frequency and high-frequency power. No significant relation was found in preadolescents. During standing, adolescents had a more marked increase in diastolic arterial pressure, heart rate, low frequency of R-R intervals, and low frequency of arterial pressure compared with those of preadolescents. Changes in diastolic pressure showed a significant negative correlation with changes in high frequency of R-R intervals. CONCLUSION: Cardiovascular autonomic function plays an important role in increasing blood pressure levels associated with increased modulation of vagal tone of the heart after puberty but does not in the preadolescent.

Work content and satisfaction before and after a reorganisation of data entry work.

The aim of the study was to analyse the psychosocial and physical effects of a reorganisation of data entry work at a data processing unit with 153 employees. The reorganisation was planned to redistribute the repetitive work and improve health and satisfaction as well as efficiency. Methods used were questionnaires and, for a sub-group of 22 participants, interviews, diaries and video recordings. During the one-and-a-half-year study period the data processing unit was closed down and the employees transferred to units with more varied tasks. The reorganisation gave opportunities to improve working conditions. The results of this study show that important improvements were achieved. The majority of the 22 participants got less data entry work and the changes permitted a better work-load distribution. However, the work content after the reorganisation still did not provide satisfactory mental variation for most of the subjects, and the changes did not seem to affect health complaints.

Autonomic function in children with type 1 diabetes mellitus.

We investigated autonomic function in 58 children and young adults with Type 1 diabetes mellitus (aged 7-22 years, duration from 3 to 18, 8.6 +/- 3.4 years) and in 74 healthy controls (6-21 years) using power spectral analysis of blood pressure and heart rate in addition to conventional standard autonomic function tests: deep breathing, the Valsalva manoeuvre, and a standing test. None of the diabetic patients were symptomatic. Reproducibility of the tests was assessed by determining the coefficient of variation in 9 controls (7.8-37.7%). Thirteen per cent of the subjects had difficulty in adequately performing the Valsalva manoeuvre. After adjustment for age, sex, body mass index, and respiratory frequency, results of the Valsalva manoeuvre and deep breathing were not different between patients and controls and there was no significant postural reduction in systolic blood pressure (> or = 20 mmHg) in the patients. Heart rate variation in the supine position during natural breathing was low in patients, although power spectral analysis of heart rate variation did not show a significant decrease in the power density in the high and the low frequency in patients compared to healthy controls. Beat-to-beat blood pressure fluctuation was significantly lower in patients and correlated with metabolic control (mean annual haemoglobin A1c), but not with disease duration and was abnormal in 7 diabetic children (12%). In contrast, tests of vagal activity were not impaired in the patients in this age range. We concluded that vagal involvement in Type 1 diabetic patients determined by spectral analysis of R-R intervals in addition to conventional tests is uncommon, but that beat-to-beat blood pressure variation was more likely to be affected.

Computer mouse or Trackpoint--effects on muscular load and operator experience.

The aim of the study was to evaluate four different modes of human-computer interaction. The modes were: use of the keyboard alone as input device, use of keyboard and mouse, use of keyboard and mouse with a three-dimensional arm support, and use of a keyboard with a Trackpoint device in its centre. Ten women and 10 men volunteered to participate. Questions asked were whether working in the different modes influenced shoulder and forearm muscular load differently during word processing, and how much strain on the neck, shoulder and arms subjects perceived in the different modes. Muscular load was studied with electromyography in three shoulder muscles and three forearm muscles. The subjects also rated the different modes in one questionnaire concerning perceived strain and in one concerning preference for any of the modes tested. Intra-individual analysis for each muscle and mode showed two possible ways of decreasing the strain from computer mouse work on the shoulder muscles--either to use Trackpoint or to use the mouse combined with the movable arm support. However, both of these computer-interaction modes increased the muscular load in the hand and forearm.

Upper-arm elevation during office work.

The present aim was to measure and quantify upper-arm elevation and to find how changed work organization and work tasks influence arm movement during a working day. Sixteen female office workers participated in the study. Their main work was statistical data entry. Upper-arm elevation was measured on two occasions separated by 18 months, i.e., before and after a change of work organization. The measurements were performed during the whole of one ordinary working day. The differences between the two measurements were mostly non-significant. Arm elevation remained essentially below 30 degrees during the main time of the working day, and the subjects worked with limited arm movements. Despite new alternative office tasks, they did not achieve a change in their habitual arm postures, or in their neck-and-shoulder disorders.

Amplitude and timing of electromyographic activity during sprinting.

The aim of this study was to make descriptive analyses of the muscle activities in the lower extremity during maximal sprinting. Nine healthy sprinters were examined during maximal sprinting using telemetric electromyography (EMG). Seven muscles of the lower extremities were investigated: biceps femoris, medial hamstrings (semimembranosus and semitendinosus), rectus femoris, gluteus maximus, tibialis anterior, lateral gastrocnemius and medial gastrocnemius. The recorded EMG levels during running were expressed as percentage of maximum voluntary isometric contractions (%max EMG). For each muscle, the normalized EMG was plotted during the whole running stride cycle and is presented for each muscle. The reason for using this method is to show that it is possible to compare different muscle activities in a runner as well as to make comparisons between runners. Lateral and medial hamstrings and gluteus maximus showed similar activities with peak levels of EMG during foot-strike. Rectus femoris had a two-peak activity, with one peak at the middle of the stance phase and the other during the swing phase. The tibialis anterior also showed a two-peak activity, but with the peaks at the beginning of the swing phase and just before foot-strike. The highest activities of the medial and lateral gastrocnemius occurred just before toe-off.

Electromyographic activity during typewriter and keyboard use.

This study investigated how ergonomic design influences neck-and-shoulder muscle strain, through keyboard assessment. Muscular activity was measured electromyographically (EMG) from six muscles in the forearm and shoulders of eight experienced typists using each of five different types of keyboard: one mechanical, one electromechanical, and one electronic typewriter; one personal computer/word processor (PC-XT) keyboard; and one angled at 20 degrees in the horizontal plane. The impact on muscular activity of using a palmrest was also studied. The mechanical typewriter induced a higher strain in the forearm and finger muscles than did the modern typewriters and keyboards. These induced no different strain on the neck-and-shoulder muscles, except for the right shoulder muscle, which was more active with the electronic typewriter than with the other machines. Using a palmrest did not decrease the strain on the muscles investigated. Use of the 'angled' PC-XT keyboard did not influence the measured muscular load on the forearm and finger muscles compared to typing on an ordinary PC-XT keyboard, but decreased the extensor muscular strain compared to the electronic typewriter.

Effects of precision and force demands, grip diameter, and arm support during manual work: an electromyographic study.

Musculoskeletal disorders in the neck, shoulder, and arm are common in some occupational groups, and have been ascribed to high precision demands and sustained static load in the neck-shoulder region. In order to evaluate the influence of precision and force demands in manual work related to arm support, instrument grip size, the muscular activity in neck, shoulder, and arm muscles was recorded by electromyography. This EMG and perceived exertion were estimated during a simulated work situation where 12 subjects followed a rotating track, using a handheld dental instrument. Normalized mean EMG amplitude levels (% reference maximal contraction) were calculated. The analysis of variance of the results showed that (a) the precision factor affected significantly the muscular load of the two dominant muscles with postural stabilization function (extensor carpi radialis and infraspinatus); (b) the force factor itself had no specific influence on the muscular load of the investigated muscles; (c) arm support, but not hand support, was of significant importance for the load of three dominant shoulder muscles (trapezius, supraspinatus, and anterior deltoid); and (d) the two different hand grip diameters did not change the activity of any muscle investigated.

An electromyographic study of dental work.

Musculoskeletal disorders are common among dentists, and have been ascribed to the demands of high precision work and sustained static loading in the neck-shoulder region, combined with a flexed and rotated cervical spine. In order to determine muscular load levels during dentistry, activity in neck, shoulder, and arm muscles was recorded using an electromyography technique (EMG). Normalized mean, median, 10th and 90th percentile EMG amplitude levels (% maximal reference contraction, %max-RVC) were calculated during ordinary dental work. Among the muscles investigated, the trapezius muscle on both sides had the highest mean (the right trapezius 9.0% and the left 7.6% of max-RVC) and 10th percentile amplitude levels (both about 2% of max-RVC). The trapezius muscles showed similar myoelectric activity on the right and left side, probably because of similar muscular static load on the both sides. The right extensor carpi radialis muscle had a significantly higher muscular load level than the left one, possibly due to stabilization demands on the dominant wrist during demanding precision work. The infraspinatus muscle had low activity level on both sides, reflecting that the dentists worked with a small degree of arm elevation and external rotation. The dentistry work thus seems to generate relatively high muscular load on both trapezius and dominant extensor-carpi-radialis, and relatively low load on the infraspinatus muscle.

Tibiofemoral joint forces during isokinetic knee extension.

Using a Cybex II, eight healthy male subjects performed isokinetic knee extensions at two different speeds (30 and 180 deg/sec) and two different positions of the resistance pad (proximal and distal). A sagittal plane, biomechanical model was used for calculating the magnitude of the tibiofemoral joint compressive and shear forces. The magnitude of isokinetic knee extending moments was found to be significantly lower with the resistance pad placed proximally on the leg instead of distally. The tibiofemoral compressive force was of the same magnitude as the patellar tendon force, with a maximum of 6300 N or close to 9 times body weight (BW). The tibiofemoral shear force changed direction from being negative (tibia tends to move posteriorly in relation to femur) to a positive magnitude of about 700 N or close to 1 BW, indicating that high forces arise in the ACL when the knee is extended more than 60 degrees. The anteriorly directed shear force was lowered considerably by locating the resistance pad to a proximal position on the leg. This model may be used when it is desirable to control stress on the ACL, e.g., in the rehabilitative period after ACL repairs or reconstructions.

Efficiency of pedal forces during ergometer cycling.

The aim of this study was to record the forces applied to the pedal during ergometer cycling and to calculate the effectiveness of these force vectors. Six healthy subjects rode a weight-braked bicycle ergometer at different work loads, pedaling rates, saddle heights, and pedal foot positions. The left lower limb and crank motions were recorded by a cinefilm camera and pedal reaction forces by a Kistler force measuring transducer mounted on the left pedal. The force effectiveness was computed as a ratio between the force tangential to instantaneous direction of pedal movement and the resultant force. The mean force efficiency ratio significantly increased by an increase of the ergometer work load or use of the anterior foot position instead of the posterior. It was not significantly changed due to alterations of the pedaling rate or saddle height.

Mechanical muscular power output and work during ergometer cycling at different work loads and speeds.

The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints.

Muscular function during ergometer cycling.

Quantified EMG and calculated mechanical muscular power output data were combined to provide further analysis of muscular function during ergometer cycling. The single-joint muscles; gluteus maximus, gluteus medius, vastus medialis, vastus lateralis and soleus all showed a more predictable function with approximately linear relationship between calculated power output and recorded EMG. The function for the two-joint muscles was found to be more complex. Biceps femoris seemed to act mainly as a hip extensor and medial hamstring mainly as a knee flexor. Gastrocnemius medialis was proposed to act more as a plantar flexor and gastrocnemius lateralis as a knee flexor.

Patellofemoral joint forces during ergometric cycling.

We estimated the patellofemoral joint forces generated during pedaling on a bicycle ergometer. Our calculations were based on measurements from a force transducer mounted on the pedal, 16-mm cine-film sequences, and biomechanical models of the cycling motion and of the patellofemoral joint. Six healthy male subjects cycled at different work loads, pedaling rates, saddle heights, and pedal foot positions. The maximum patellofemoral compressive force was 905 N (1.3 times body weight [BW]) when cycling with an anterior foot position at 120 W, 60 rpm, and middle saddle height. The mean peak compressive force between the quadriceps tendon and the intercondylar groove was 295 N (0.4 BW), and the patellar-tendon and quadriceps-tendon strain forces were 661 N (0.9 BW) and 938 N (1.3 BW), respectively. The patellofemoral joint forces were increased with increased work load or decreased saddle height. Different pedaling rates or foot positions did not significantly change these forces.

Tibiofemoral joint forces during ergometer cycling.

Six healthy subjects pedaled on a weight-braked bicycle ergometer at different workloads, pedaling rates, saddle heights, and pedal foot positions. The subjects were filmed with a cine-film camera and pedal reaction forces were recorded from a force transducer mounted on the left pedal. Net knee moments were calculated using a dynamic model, and the tibiofemoral shear and compressive force magnitudes were calculated using a biomechanical model of the knee. During cycling at 120 W, 60 rpm, midsaddle height, and anterior pedal foot position, the mean peak tibiofemoral compressive force was 812 N [1.2 times body weight (BW)]. The maximum anteriorly directed tibiofemoral shear force was found to be low (37 N). The compressive and shear forces were significantly increased by an increased ergometer workload. The pedaling rate had no influence on the tibiofemoral force magnitudes. The stress on the ACL was low and could be further decreased by use of the anterior foot position instead of the posterior.

Power output and work in different muscle groups during ergometer cycling.

The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calculated using a model based upon dynamic mechanics described elsewhere. The mean peak concentric power output was, for the hip extensors, 74.4 W, hip flexors, 18.0 W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorption through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relationships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flexors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.

Quantified electromyography of lower-limb muscles during level walking.

The electromyography (EMG) of eleven different lower limb muscles of ten healthy subjects was quantified during normal level walking. The surface EMGs obtained were normalized, in percentage, to the activity obtained during an isometric maximum voluntary test contraction of each subject. The mean peak activities of the gluteus maximus, gluteus medius, rectus femoris, vastus medialis, vastus lateralis, biceps femoris and medial hamstring muscles occurred at heel-strike and were between 5 and 15% of max isometric EMG. The magnitudes of tibialis anterior and triceps surae muscular activity were higher than those of the other muscles investigated. Mean peak activity in tibialis anterior was 27%, in gastrocnemius medialis 42%, in gastrocnemius lateralis 19% and in soleus 40%. The important role of the triceps surae during walking was reflected in comparatively high muscular activity at push-off.

Load moments about the hip and knee joints during ergometer cycling.

The aim of the study was to calculate the magnitudes of moments of force acting about the bilateral hip and knee joint axes during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at different workloads, pedalling rates, saddle heights and pedal foot position. During cycling at 120 Watts, 60 revolutions per minute with mid-saddle height and anterior pedal foot position, the mean peak flexing and extending hip load moments were 34.3 and 8.9 Nm, respectively. Mean peak flexing knee load moments was 28.8 Nm and extending moment was 11.9 Nm. Hip load moments were significantly increased by increasing the ergometer workload or pedalling rate. For knee load moments, workload was the most important factor. The flexing knee load moment did not change with changes in pedalling rate. Different saddle heights or pedal food positions had a slight but not always statistically significant influence on the hip and knee joint loads. The maximum hip and knee joint load moments induced during cycling were small compared with those obtained during other exercises or normal activities such as level walking, stair climbing, and lifting.

The forces of ankle joint structures during ergometer cycling.

The ankle joint moment, joint compressive force, and Achilles tendon force obtained during ergometer cycling were calculated by using a quartz force-measuring transducer mounted on the pedal. Six healthy subjects rode in 11 different ways at different workloads, pedalling rates, saddle heights, and pedal foot positions. The mean maximum dorsiflexing load moment about the ankle joint during standardized ergometer cycling was calculated to 30.9 nm. The mean ankle joint compressive force and mean Achilles tendon force measured 1008 N (1.4 times body weight) and 762 N (1.1 times body weight), respectively. The ankle joint moment was significantly changed by a change of workload or pedal foot position.

Muscular activity during ergometer cycling.

The aim of the study was to quantify the activity as recorded by electromyography during ergometer cycling in eleven different muscles of the lower extremity. Eleven healthy subjects rode in twelve different ways at different work-load, pedalling rate, saddle height and pedal foot position. Vastus medialis and lateralis, gastrocnemius medialis and lateralis and the soleus muscle were the most activated muscles. Changes in muscle activity during different calibrations were studied in eight of the eleven muscles. An increase in work-load significantly increased the mean maximum activity in all the eight muscles investigated. An increase of the pedalling rate increased the activity in the gluteus maximus, gluteus medius, vastus medialis, medial hamstring, gastrocnemius medialis and soleus muscles. An increase of the saddle height increased the muscle activity in the gluteus medius, medial hamstring and gastrocnemius medialis muscles. Use of a posterior pedal foot position increased the activity in the gluteus medius and rectus femoris muscles, and decreased the activity in the soleus muscle.