Mechanical load on the low back and shoulders during pushing and pulling of two-wheeled waste containers compared with lifting and carrying of bags and bins.

OBJECTIVE: Compare the mechanical load on the low back and shoulders during pushing and pulling a two-wheeled container with the load during lifting and carrying the same amount of waste. BACKGROUND: Only little is known about risk factors and mechanical loads during push/pull operations. DESIGN: A complete 2(3) factor push/pull experiment. A two-wheeled container with 25 or 50 kg was pushed in front of and pulled behind the body by seven waste collectors. Further, the same subjects lifted and carried a paper bag and a dustbin both loaded with 7 and 25 kg. METHOD: All operations were video recorded and the push/pull force was measured by means of a three-dimensional force transducer. Peak Motus and Watbak software were used for digitising and calculation of torque at L4/L5 and the shoulder joints and compression and shear forces at L4/L5. RESULTS: During pushing and pulling the compression at L4/L5 is from 605 to 1445 N. The extension torque at L4/L5 produced by the push/pull force is counteracted by the forward leaning of the upper body. The shear force is below 202 N in all situations. The torque at the shoulders is between 1 and 38 Nm. CONCLUSION: In the present experiments the torques at the low back and the shoulders are low during pushing and pulling. No relation exists between the size of the external force and the torque at the low back and the shoulder. RELEVANCE: Pushing and pulling are common in many workplaces and have often replaced lifting and carrying situations. This has emphasised the need for more knowledge of the internal mechanical load on the body during these activities.

Effects of drug-induced changes in resting blood pressure on classically conditioned heart rate and blood pressure in restrained rats.

Subsequent to receiving aversive classical conditioning, which led to a decelerative heart rate (HR) conditioned response (CR) and a pressor-depressor blood pressure (BP) CR, three separate groups of restrained rats received intravenous infusion of sodium nitroprusside (40 micrograms/mg/min) to lower baseline BP, phenylephrine (17 micrograms/mg/min) to raise baseline BP, or an equivalent volume of saline. Conditioning test trials during infusion revealed that hypotension produced by sodium nitroprusside eliminated the HR CR and transformed the BP CR into a pressor-only reaction. Hypertension produced by phenylephrine facilitated the HR CR and changed the BP CR to a pressor-only response on selected trials in which baseline BP increases and baseline HR decreases were within restricted limits. Following drug withdrawal, the HR CRs of both drug groups and the BP CR of the phenylephrine group were attenuated. The unconditioned responses to the shock unconditioned stimulus under phenylephrine were exaggerated and consisted of tachycardias and depressor BP changes, whereas under sodium nitroprusside reduced tachycardias and depressor activity occurred. The results suggested that the loss of the vagally mediated HR CR under sodium nitroprusside was due to baroreceptor-controlled inhibition of vagal discharge and that the enhancement of the HR CR under phenylephrine was due to baroreceptor-influenced facilitation of vagal discharge.