Sick leave analysis among self-employed Dutch farmers.

BACKGROUND: Agriculture is one of the most physically demanding and risky industries. Aim The objective of this study was to provide baseline data on the diagnoses, occurrence and duration of sick leave of self-employed Dutch farmers. METHOD: A database of 22 807 sick leave claims of 12 627 farmers during the period 1994-2001 was analysed. RESULTS: Most of the claims (61%) were for musculo-skeletal injuries and disorders. The mean cumulative incidence (CI) was 10.2 claims per year per 100 farmers and did not change over time. However, it varied per agricultural sector and per age category, being lowest in arable farming and in the youngest age category and highest in mushroom farming and in the oldest age category. The duration of sick leave depended both on diagnosis and age category: the slowest recovery from sick leave was seen in farmers with respiratory diseases and farmers in the oldest age category. CONCLUSION: The results make it easier to identify groups of farmers to be targeted to prevent sick leave. To reduce the occurrence of sick leave in agriculture, the strategy should be to prevent musculo-skeletal injuries and disorders. Furthermore, a sector-specific approach is recommended, so that preventive actions can be focused on working conditions-specifically on workload and work safety. Efforts to shorten the duration of sick leave will also be valuable to obtain a reduction of sick leave.

Evaluation of work-rest schedules with respect to the effects of postural workload in standing work.

The influence of four work-rest schedules (60-min shift-15-min break, 45-15, 30-15, 30-30) on acute effects of physical workload in the back and legs due to standing work was investigated in 12 poultry inspectors. Subjective discomfort in the legs and back, and swelling in the distal lower leg were significantly affected, with the 60-15 schedule leading to a higher postural load as compared with the other schedules. No effect on spinal shrinkage was found. It was concluded that the 60-15 schedule should be avoided. An optimal work-rest schedule considering visco-elastic deformation of the spine would probably involve frequent short breaks, whereas longer breaks would seem more effective considering leg swelling.

The use of the relation between relative force and endurance time.

The relation between relative force (i.e., the actual force relative to the maximal voluntary force) and endurance time (i.e., the time the force can be maintained) is employed in a number of methods for ergonomics research. The aim is to assess the development of localized muscular fatigue as a consequence of isometric contractions and to compare activities regarding both the intensity and the duration of the isometric contractions exerted. The main assumption underlying this approach is that the relation is identical for different muscles and in different situations. Several anatomical and physiological factors contributing to variation in the relation are discussed and the consequences of this variation for the validity of the methods employing the relation are quantified. From this analysis, it appears, that the use of the relation between relative force and endurance time with the assumption mentioned leads to unreliable results. Therefore assessment of isometric contractions in labour situations will have to be based on fundamentally different methods.

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.

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.

Analysis of vasomotion waveform changes during pressure reduction and adenosine application.

Changes in the vasomotion waveform were studied in transverse arterioles (TAs) and their first-order side branches (FOSs) in the tenuissimus muscle of 14 young, anesthetized rabbits during stepwise arterial pressure reduction and local application of adenosine using intravital video microscopy. Pressure reduction resulted in a systematic increase in vasomotion cycle length (CL) and amplitude (A) concomitant with an increase in effective vascular diameter (Deff) and maximum diameter and a decrease in blood flow (Q). During adenosine application Deff and maximum diameter also increased, but CL and A did not change systematically. At moderate pressure reductions and during adenosine application CL changes were limited (less than 1.5 s) and nonsystematic, agreeing with an earlier study (D. W. Slaaf, G. J. Tangelder, H. C. Teirlinck, and R. S. Reneman. Microvasc. Res. 33: 71-80, 1987). In TAs these changes resulted from changes in both the dilation and the constriction phase. In FOSs, however, changes in CL were caused by prolongation of the dilation phase alone. At greatly reduced pressure levels, the CL increase was more pronounced and in both TAs and FOSs was caused by plateau formation in the dilation phase. Stretch of the arteriolar wall does not seem to play a role in control of the vasomotion waveform. Because the onsets of dilation always occur synchronously in TAs and FOSs, but the onsets of constriction do not, vasomotion seems to be a series of rhythmic dilations.

Changes in vasomotion pattern and local arteriolar resistance during stepwise pressure reduction.

Changes in vasomotion parameters and their consequences for local arteriolar resistance were studied in transverse arterioles and their first order side branches in the tenuissimus muscle of 10 young urethane anesthetized rabbits during stepwise reduction of arterial pressure, using intravital microscopy. To assess the influence of vasomotion on mean local arteriolar resistance, the effective vascular diameter, as a measure of mean flow carrying capacity, was calculated. The contribution of vasomotion to the mean local resistance is limited in transverse arterioles, but important in first order side branches, dominating the flow fluctuations in the downstream capillaries. During pressure reduction, an over-all increase in vasomotion cycle length and amplitude was found in both transverse arterioles and first order side branches, concomitant with an increase in effective arteriolar diameter and a decrease in local blood flow and reduced velocity, as a measure of wall shear rate. Flow autoregulation was observed in 70% of the arterioles. The changes in cycle length and amplitude showed only limited correlations with local blood flow, reduced velocity, arterial pressure and effective arteriolar diameter. This indicates that it is unlikely that only one of these variables is responsible for the changes in the vasomotion parameters.

Does capillary recruitment exist in young rabbit skeletal muscle?

Recruitment of terminal arterioles and capillaries was studied in the tenuissimus muscle of 16 young urethane anesthetized rabbits. In one set of experiments (8 animals) intravital fluorescence microscopy was used to visualize transverse arterioles and to assess the number of their first order side branches (functionally the terminal arterioles) perfused with red blood cells before and after vasodilation (10(-4)M adenosine, applied topically). In another set of experiments (8 animals) the number of muscle capillaries perfused with red blood cells from the same parent arteriole was determined at rest and during vasodilation (reactive hyperemia), using bright field microscopy. All capillaries and first order side branches that were perfused during vasodilation were also perfused at rest. These findings indicate that in this skeletal muscle preparation no recruitment of arterioles or capillaries occurs in an anatomical sense of the word.

Flow cessation pressures in the rabbit tenuissimus muscle.

Cessation of muscle capillary flow was studied in rabbit tenuissimus muscle, using intravital microscopy. Perfusion pressure was reduced by arterial occlusion or simultaneously elevated venous and tissue pressure. Muscle capillary flow ceased in the presence of arteriolar dilation at a median perfusion pressure of 17.5 mmHg during arterial occlusion and at 25.3 mmHg in case of simultaneously increased tissue and venous pressure. The pressure difference of 7.8 mmHg was confirmed in a series of experiments where arterial occlusion and increased tissue pressure were randomly alternated in the same animal. The mechanisms responsible for the difference in pressure level at which flow ceases in the capillaries under these circumstances are incompletely understood. Possible mechanisms are discussed.

Oxygen consumption and speed of cycling using an air-resistance simulator on a hometrainer roller.

Oxygen consumption was determined for subjects cycling on a hometrainer roller with a racing bicycle. In part of the experiments the bicycle was supplied with an air-resistance simulator. The relation between oxygen consumption and velocity of cycling on the roller is linear: similar to that during bicycle ergometry. The relation is almost the same as during bicycling outdoors on a touring bicycle when the simulator is used while cycling on the roller. Cycling with the simulator only on the bicycle on a support is comparable to cycling outdoors on a racing bicycle. It is concluded that the use of a roller and an air-resistance simulator can be used for ergometry and training.