Mechanical Workload Research Articles

Multisite musculoskeletal pain among young technical school students entering working life.

BackgroundThere is a need to investigate the occurrence of multisite pain in young adults and to determine potential factors contributing to the early course of multisite musculoskeletal pain. The aim of this prospective study was to assess the occurrence and change of prevalence in the number of pain sites. We also wanted to identify work-related and individual risk factors associated with the number of musculoskeletal pain sites.MethodsWe monitored musculoskeletal pain from 4 body regions, individual and work-related factors on 21 occasions over a 6.5 year period. The cohort consisted of 420 technical school students entering working life. Data were analyzed by generalized estimating equations (GEE).ResultsPain from more than one body site was prevalent in this cohort of young adults (69 % at baseline), and the number of body sites in pain was found quite stable over the 6.5 year follow-up period. Women had higher number of pain sites compared with men and gender specific risk factors were identified. Increased mechanical workload and quantitative demands and low socioeconomic status were associated with increased number of musculoskeletal pain sites among women, while tobacco use was found as a risk factor among young men. Increased perceived muscle tension was the only factor significantly associated with increased number of pain sites in both genders.ConclusionThe current study supports earlier findings and show that pain from multiple body sites are frequent also among young workers. The identification of gender specific risk factors in our study is important and may facilitate practical prevention and future research.

Work with prolonged arm elevation as a risk factor for shoulder pain: A longitudinal study among young adults

This prospective study aimed at examining if work with prolonged arm elevation predicts shoulder pain among 41 young adults in their first years of working life. Fifteen hairdressers, 15 electricians, 5 students and 6 with various work were followed over a 2.5-year period (2006/7–2009). Arm elevation was measured with inclinometers during a full working day at baseline. Shoulder pain was reported at baseline and twice in the follow-up period. Data were analyzed by generalized estimating equations (GEE-analysis), stratified by gender and adjusted for time, mechanical workload, work demand, physical activity, tobacco use and prior shoulder pain. Work with prolonged arm elevation with angles >60° and >90° were associated with shoulder pain among women. Even though the shoulder pain levels are low the study suggests work with arms elevated as an early work-related risk factor among women, and indicates the importance of early prevention strategies.

A longitudinal study on risk factors for neck and shoulder pain among young adults in the transition from technical school to working life.

The study examined the course of neck and shoulder pain among a cohort of technical school students entering working life. We also aimed to identify work-related and individual risk factors for neck and shoulder pain during this transition period. The study was designed as a prospective cohort study following 420 technical school students (167 student hairdressers, 118 student electricians, and 135 media/design students) from school, through their apprenticeship and into working life. Every 4 (th)month over a 6.5 year period (2002-2009), the participant`s neck and shoulder pain for the preceding four weeks was assessed. Mechanical and psychosocial workplace factors as well as individual factors were evaluated at baseline and/or during the follow-up period. Data were analyzed by generalized estimating equations (GEE). We found a significant increase in neck and shoulder pain over time in the transition from technical school to working life. High mechanical workload was associated with neck and shoulder pain among women, while a high level of shoulder muscle endurance capacity was associated with lower rates of neck and shoulder pain among men. Perceived muscle tension and ethnicity were the most consistent predictors for neck and shoulder pain, found among both women and men. Increased neck and shoulder pain was found in the transition from technical school to working life, and both work-related and individual factors were associated with pain development.

Mechano-electrical coupling as framework for understanding functional remodeling during LBBB and CRT.

It is not understood why, after onset of left bundle-branch block (LBBB), acute worsening of cardiac function is followed by a further gradual deterioration of function, whereas most adverse cardiac events lead to compensatory adaptations. We investigated whether mechano-electrical coupling (MEC) can explain long-term remodeling with LBBB and cardiac resynchronization therapy (CRT). To this purpose, we used an integrative modeling approach relating local ventricular electrophysiology, calcium handling, and excitation-contraction coupling to global cardiovascular mechanics and hemodynamics. Each ventricular wall was composed of multiple mechanically and electrically coupled myocardial segments. MEC was incorporated by allowing adaptation of L-type Ca(2+) current aiming at minimal dispersion of local external work, an approach that we previously applied to replicate T-wave memory in a synchronous heart after a period of asynchronous activation. LBBB instantaneously decreased left-ventricular stroke work and increased end-diastolic volume. During sustained LBBB, MEC reduced intraventricular dispersion of mechanical workload and repolarization. However, MEC-induced reduction in contractility in late-activated regions was larger than the contractility increase in early-activated regions, resulting in further decrease of stroke work and increase of end-diastolic volume. Upon the start of CRT, stroke work increased despite a wider dispersion of mechanical workload. During sustained CRT, MEC-induced reduction in dispersion of workload and repolarization coincided with a further reduction in end-diastolic volume. In conclusion, MEC may represent a useful framework for better understanding the long-term changes in cardiac electrophysiology and contraction following LBBB as well as CRT.

The Association Between Combination of Hand Force and Forearm Posture and Incidence of Lateral Epicondylitis in a Working Population

The objective of this prospective study is to investigate the exposure-response relationships between various workplace physical exposures of force, repetition, and their combination assessed at an individual level with lateral epicondylitis (LE). Workplace upper extremity musculoskeletal disorders (UEMSDs) are prevalent, disabling, and expensive. LE is one of the major UEMSDs in active workers. We used detailed health history, symptoms, and physical examination for identifying incidence and detailed exposure assessment to capture work tasks of each worker and to measure quantitative mechanical workload. We used counting process style input of proportional hazards regression for modeling cumulative incidence that accounts for changed exposure estimates during the follow-up period when respondents change jobs. The incidence rate of LE on the dominant side was 4.91 per 100 person-years. Adjusted for age and gender, the combined effect of forearm pronation > or = 45 degrees for > or = 40% of time and time spent with forceful exertion, including any power grip (hazard ratio [HR] = 2.8, 95% confidence interval [CI] = [1.35-5.77]), lifting for > or = 3% of time (HR = 2.50, 95% CI = [1.19-5.24]), and duty cycle for forceful exertion for > or = 10% (HR = 2.25, 95% CI = [1.09-4.66]), were significant predictors of dominant side LE, whereas neither the awkward posture nor the forceful exertion alone was significant. Older workers with jobs requiring a high percentage of time working with force in combination with awkward postures of forearm were more likely to predict LE. This study shows the evidence of the etiologic role of strenuous manual tasks in the occurrence of LE.

The effect of work-related sustained trapezius muscle activity on the development of neck and shoulder pain among young adults

This study aimed to evaluate if sustained trapezius muscle activity predicts neck and shoulder pain over a 2.5-year period. Forty young adults (15 hairdressers, 14 electricians, 5 students and 6 with various work) were followed during their first years of working life. Self-reported neck and shoulder pain during the last four weeks was assessed seven times over the observational period. Upper-trapezius muscle activity was measured during a full working day by bilateral surface electromyography (EMG) at baseline (winter 2006/7). Sustained trapezius muscle activity was defined as continuous muscle activity with amplitude >0.5% EMGmax lasting >4 minutes. The relative time of sustained muscle activity during the working day was calculated and further classified into low (0-29%), moderate (30-49%) and high (50-100%) level groups. Generalized estimating equations (GEE), adjusted for time, gender, mechanical workload, control-over-work intensity, physical activity, tobacco use, and prior neck and shoulder pain, showed that participants with a high level of sustained muscle activity had a rate of neck and shoulder pain three times higher than the low level group during a 2.5-year period. The association was strongest at the same time and shortly after the EMG measurement, indicating a time-lag of ≤6 months. The results support the hypothesis that sustained trapezius muscle activity is associated with neck and shoulder pain. This association was strongest analyzing cross-sectional and short-term effects.

The influence of a unilateral fixed ankle on metabolic and mechanical demands during walking in unimpaired young adults

The plantarflexors provide a major source of propulsion during walking. When mechanical power generation from the plantarflexor muscles is limited, other joints may compensate to maintain a consistent walking velocity, but likely at increased metabolic cost. The purpose of this study was to determine how a unilateral reduction in ankle plantarflexor power influences the redistribution of mechanical power generation within and across limbs and the associated change in the metabolic cost of walking. Twelve unimpaired young adults walked with an ankle brace on the dominant limb at 1.2m/s on a dual-belt instrumented treadmill. Lower extremity kinematics and kinetics as well as gas exchange data were collected in two conditions: (1) with the brace unlocked (FREE) and (2) with the brace locked (FIXED). The brace significantly reduced ankle plantarflexion excursion by 12.96±3.60° (p<0.001) and peak ankle mechanical power by 1.03±0.51W/kg (p<0.001) in the FIXED versus FREE condition. Consequently, metabolic power (W/kg) of walking in the FIXED condition increased by 7.4% compared to the FREE condition (p=0.03). Increased bilateral hip mechanical power generation was observed in the FIXED condition (p<0.001). These results suggest that walking with reduced ankle power increases metabolic demand due to the redistribution of mechanical power generation from highly efficient ankle muscle-tendons to less efficient hip muscle-tendons. A within and across limb redistribution of mechanical workload represents a potential mechanism for increased metabolic demand in pathological populations with plantarflexion deficits or those that walk with an ankle–foot orthosis that restricts range of motion.

Pain and mechanical injury of human skin following needle insertions.

Needle insertion is a very common invasive procedure, but little has been done to study how pain is related to the mechanical properties of the needle insertion, and how pain from the procedure may be minimized. The aim of the present study was to investigate the pain evoked by standardized needle insertion into the human skin. Needle insertions were performed with continuous registration of the mechanical force on the needle. Forty consecutive needle insertions to the depth of 8 mm with 27G and 30G needles, 2 and 19 mm/s velocities, and at 45 and 90 degree angles to the skin surface were performed in a randomized and blinded design in 30 healthy volunteers. The occurrence, intensity and quality of pain, as well as the maximum mechanical needle penetration force and the total mechanical workload were registered. The mechanical parameters of needle insertions were significantly related to needle size and velocity of insertion. Occurrence of pain and bleeding were significantly related to the needle size. High needle insertion velocity was significantly related to a higher rate of sharp and pricking pain, and low insertion velocity to a significantly higher rate of dull and burning pain. The present study provides quantitative data on pain and mechanical parameters of standardized needle insertions through normal human skin. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.

Long periods with uninterrupted muscle activity related to neck and shoulder pain

The aim was to analyze the relationship between periods with uninterrupted neck muscle activity for ≥ 4 min and neck and shoulder pain. The trapezius muscle activity was recorded bilaterally on 40 young workers and students during a full shift. Neck and shoulder pain, mechanical work load and decision control were reported at the same time as the muscle activity recording and 6 months later. A dose-response relationship was found between uninterrupted muscle activity and neck and shoulder pain, with a ten-fold higher risk for the group with more than half, compared to less than a third, of the shift with uninterrupted muscle activity. Self-reported mechanical work load showed a small but protective effect related to pain. Gender and decision control did not emerge as important risk factors in this model. In conclusion, this study indicates that work or other exposures that contains long periods with uninterrupted neck muscle activity of 4 min duration or longer should be minimized to reduce risk of neck and shoulder pain.

Analysis of the Mechanical Work Load of the Plunger in the Multi-Biting Test of the Batter of Wheat Flour

Analysis of the Mechanical Work Load of the Plunger in the Multi-Biting Test of the Batter of Wheat Flour

Relation of airway obstruction and respiratory muscle weakness to energy metabolism in pulmonary emphysema

Resting energy expenditure (REE) was assessed and its relationship to nutritional status, pulmonary function and respiratory muscle function was studied in 25 patients with pulmonary emphysema. The mean value of REE was 1413 +/- 251 Cal and the ratio of REE/REEpred was 1.398 +/- 0.23, suggesting the existence of a hypermetabolic state in these patients. REE/REEpred ratio was inversely correlated with plasma amino acid BCAA/AAA ratio and body muscle mass; and PImax. REE was inversely correlated with FEV1.0%. REE in the patient subgroup with severe hyperinflation (%RV > or = 200) was significantly higher than that in the subgroup with moderate hyperinflation. Malnourished patients showed significantly more severe hyperinflation than well-nourished patients. These findings suggest that augmented REE contributes to malnutrition in patients with emphysema, and that the increase in REE was related to the increase in mechanical work load on the basis of airway obstruction, respiratory muscle weakness and hyperinflation.

Calcium sensitisation impairs diastolic relaxation in post-ischaemic myocardium: implications for the use of Ca2+ sensitising inotropes after cardiac surgery☆

Calcium sensitising inotropes are increasingly being used in cardiac surgical patients. Theoretically, increasing contractile protein sensitivity to Ca(2+) prevents the Ca(2+) elevation associated arrhythmogenicity and potentiates the inotropic effect of catecholamines. On the other hand, we hypothesised that Ca(2+) sensitisation exacerbates post-ischaemic myocardial stunning by impairing diastolic relaxation, which might have deleterious effects in postoperative cardiac surgical patients. In an isolated rabbit heart model, 45 min normothermic ischaemia with potassium-induced cardioplegic arrest was followed by 120 min reperfusion. Isovolumetric left ventricular (LV) function and myocardial oxygen consumption (MvO(2)) were measured, and cytosolic Ca(2+) was monitored by rhod-2 surface spectrofluorometry. During reperfusion, ORG 30029 (250 microM) and levosimendan (0.5 microM) were used as Ca(2+) sensitisers (ORG, n=6, Levo, n=6), Ca(2+) de-sensitisation was induced with butanedione-monoxime (5mM, BDM, n=6), and dopamine (20 nM) served as a representative catecholamine (n=6). To counteract the PDE III inhibiting properties of ORG and Levo, IGF-1 (0.1 microM) and parathyroid hormone (0.05 microM) were used. As expected, ischaemia/reperfusion induced moderate cytosolic calcium overload. Dopamine increased LV contractility and MvO(2) by augmenting the amplitude of the Ca(2+) transient, but relaxation was unchanged due to faster diastolic Ca(2+) removal. Dopamine-induced Ca(2+) handling was unchanged after uncoupling the Mg-ATPase with BDM, and MvO2 decreased in proportion with the reduced LV mechanical work load. ORG improved contractility without apparent effects on Ca(2+) handling, and MvO(2) remained constant despite increased contractile work. Conversely, ORG induced a rightward shift of the diastolic pressure-volume relationship in post-ischaemic hearts (diastolic pressure at 0.8 ml balloon volume 14.3+/-5 mmHg, p=0.01 vs control), but not in non-ischaemic control hearts. With levosimendan, the Ca(2+) sensitising effects were less pronounced (7.6+/-3 mmHg, p=0.4 vs control). By counteracting the PDE inhibiting effects of ORG and Levo using parathyroid hormone and IGF-1, the negative lusotropic effects of Ca(2+) sensitisation were unmasked. Calcium sensitisation improves systolic function and energetic efficiency. However, Ca(2+) sensitisers should be used with caution during post-ischaemic reperfusion, as they may exacerbate myocardial stunning and thus impair cardiac output.

Psychological and mechanical workload and musculoskeletal symptoms among female child-care workers

The aim was to test a structural model of the relations between psychological and mechanical workload and musculoskeletal neck/shoulder symptoms. This two-wave longitudinal cohort study was based on a questionnaire survey among Swedish female child-care workers (n=789). Two models were tested using structural equation modelling, one containing only those participants considered symptom free at baseline, thus focusing on symptom development, and one containing all participants irrespective of their baseline musculoskeletal status. The results indicate that psychological workload was related to the development of neck/shoulder symptoms, and thus highlight the importance of addressing psychosocial work environment factors in organization design and workplace interventions. However, psychological workload was not related to symptoms (when controlling for baseline mechanical workload and symptoms) in the model not distinguishing between different symptoms processes. These findings point to the importance of distinguishing between different processes such as development, maintenance and recovery from symptoms in studies of workplace factors and musculoskeletal symptoms. Mechanical workload was not related to neck/shoulder symptoms, when controlling for baseline psychological workload and symptoms, in any of the models tested. No interaction effect was found for psychological and mechanical workload on neck/shoulder symptoms.

Central AT1 receptor blockade increases metabolic cost during exercise reducing mechanical efficiency and running performance in rats

The effect of central angiotensin AT(1) receptor blockade on metabolic rate and running performance in rats during exercise on a treadmill (18 m x min(-1), 5% inclination) was investigated. Oxygen consumption (VO(2)) was measured, using the indirect calorimetry system, while the animals were exercising until fatigue after injection of 2 microL of losartan (Los; 60 nmol, n=9), an angiotensin II AT(1) receptor antagonist, or 2 microL of 0.15 M NaCl (Sal, n=9) into the right lateral cerebral ventricle. Mechanical efficiency (ME) and workload (W) were calculated. The W performance by Los-treated animals was 29% lesser than in Sal-treated animals (p<0.02). During the first 10 min of exercise (dynamic state of exercise), there was a similar increase in VO(2), while ME remained the same in both groups. Thereafter (steady state of exercise), VO(2) remained stable in the Sal group but continued to increase and stabilized at a higher level in Los-treated animals until fatigue. During the steady state of exercise there was a sharper reduction in ME in Los-treated rats compared to Sal-treated animals (p<0.01) that was closely correlated to W (r=0.74; p<0.01). Our data showed that AT(1) receptor blockade increases metabolic cost during exercise, reducing mechanical efficiency. These results indicate that central angiotensinergic transmission modulates heat production, improving ME during the steady state of exercise.

An evaluation of cumulative probability distribution of force (CPDF) as an exposure assessment method during isometric non-isotonic shoulder abductions

A study was conducted with an objective of evaluating cumulative probability distribution of force (CPDF) as a method for assessing exposures to mechanical workload during dynamic activities. In a supine posture, participants adopted 90° shoulder abductions, and maintained this posture against time-varying resistance until exhaustion (1 hr max.). External forces were generated by a mechanism consisting of a rotating dynamometer connected to a set of springs and light steel cables, with the other end of the mechanism connected to an elbow strap. Since the participant's arm was held at a fixed location, cyclic rotating movements of the dynamometer resulted in repetitive, isometric non-isotonic exertions. The 10th and the 90th percentiles of the external CPDF were set at 2.5% or 10% and 20% or 30% of maximum strength, respectively. The dynamometer angular velocity was set at 20° or 45°/s, to impose different rates of muscle contraction. Response variables included endurance time, rates of muscle strength reduction, and rates of perceived discomfort increase. The findings indicated that the CPDF method reflected differing exposures to mechanical workload, but failed to capture information on task repetitiveness. Additionally, the findings suggested the potential benefit of shorter work cycles and the use of subjective ratings for rapid assessments of short-term performance outcomes. Relevance to industry The ability to quantify mechanical exposures is a prerequisite for task evaluation and determining dose–response relationships. This study evaluated the effectiveness of such an exposure assessment method.

Effect of tidal volume and respiratory rate on the power of breathing calculation

The power of breathing (PoB) is used to estimate the mechanical workload of the respiratory system. Aim of this study was to investigate the effect of different tidal volume-respiratory rate combinations on the PoB when the elastic load is constant. In order to assure strict control of the experimental conditions, the PoB was calculated on an airway pressure-volume curve in mechanically ventilated patients. Ten patients received three different tidal volume-respiratory rate combinations while minute ventilation was constant. Respiratory mechanics, PoB and its elastic and resistive components were calculated. Alternative methods to estimate the elastic workload were assessed: elastic work of breathing per litre per minute, elastic workload index (the square root of elastic work of breathing multiplied by respiratory rate) and elastic double product of the respiratory system (the elastic pressure multiplied by respiratory rate). Despite constant elastance and minute ventilation, the elastic PoB showed an increment greater than 200% from the lower to the greater tidal volume, accounting for approximately 80% of the whole PoB increment. On the contrary, elastic work of breathing per litre per minute, elastic workload index and elastic double product did not change. Changes in breathing pattern markedly affect the PoB despite constant mechanical load. Other indexes could assess the elastic workload without tidal volume dependence. Power of breathing use should be avoided to compare different mechanical loads or efficiencies of the respiratory muscles when tidal volume is variable.

Respiratory physiopathology in surgical repair for large incisional hernias of the abdominal wall

Background: The computerized noninvasive measurement of respiratory mechanics enables new prospects in the study of respiratory physiopathology in surgical repair of large incisional hernias. Study design: We studied 10 patients with COPD ventilated with a Servo Ventilator 900C. We measured inspiratory flow by means of a pneumotacograph, the volume by integrating the flow signal, and esophageal and airway opening pressure by means of two differential pressure transducers (an esophageal balloon measures, separately, chest wall and lung mechanical properties). The signals were sent by an analogic-digital converter to a personal portable computer to be analyzed. We calculated compliance of total respiratory system (Crs), chest wall (Ccw), and lung (Cl); maximum resistance of the total respiratory system (Rmax, Rs), chest wall (Rmax, w), and lung (Rmax, L); and work of breathing (Wob). Statistics were performed using one-way analysis of variance and p = 0.05 was considered significant. Results: At the closure of the peritoneum a reduction of Crs and Wob was recorded in seven patients in whom a PTFE prosthesis widening the abdominal cavity was used to restore the baseline value. Variations in respiratory compliance are from variations in Ccw with unaffected Cl (Ccw varied from 0.180 to 0.130 L/cmH 2O at peritoneal closure and from 0.130 to 0.170 L/cmH 2O by prosthetic peritoneal widening). Respiratory resistances remained unchanged (11.3 cmH 2O/L/s) at any time of measurement. Conclusions: The intraoperative assessment of respiratory mechanics is useful to evaluate and eventually to decrease the mechanical workload (prosthesis widening peritoneum or fascia incisions). The passive mechanical work performed by the ventilator needs to be kept constant or no higher than 10% basic data: if these conditions are maintained, mostly in patients with COPD, there is no risk of respiratory muscular fatigue during the postoperative period.

Association between Assembly Work Electromyography and Discomfort as Identified by Video-Computer Interaction

The purpose of this product is to study the correlation between self-reported and measured mechanical workload of neck and shoulder on workstations level. Six persons participated in the study, each working at six different workstations. The workstations were ranked from “lowest” to “highest” workload according to different variables. The correlations were studied on ranking order. Different types of assembly work were mainly carried out in all stations. In this work (few high workload situations, and a high degree of monotonous, repetitive work situations) one situation with a high workload could in this case be experienced as positive. The methods lead to contradicting results as regards identifying work situations with high loads. The results indicate that the methods lead to similar results as regards identifying work situations with low loads.

Regional variations in pain to controlled mechanical skin traumas from automatic needle insertions and relations to ultrasonography

Background/aims: Variations in pain from needle insertions in different anatomical regions have not previously been investigated in relation to the mechanical parameters of needle insertions. The objective of the present study was to investigate these relations and furthermore to investigate possible relations between the skin parameters measured by high‐frequency ultrasound and the mechanical parameters of needle insertion.Methods: Forty‐eight needle insertions were performed in a randomised and blinded design into the deltoid region, the abdominal region, and the lateral region of the thigh in 30 healthy volunteers. The insertions were performed with hypodermic insulin needles 27 gauge (G) and 30G, at 19 mm/s, 90 degree angle, and 8 mm along the insertion axis. From each needle insertion the occurrence, intensity, and quality of pain as well as bleeding, and mechanical insertion parameters [maximum mechanical needle penetration force (N), indentation work load (10‐3 Nm), and total mechanical work load (10‐3 Nm)] were registered. Also, the skin of each anatomical region was characterised by 20‐MHz ultrasonographic examination.Results: The maximum mechanical penetration force was highest in the thigh and lowest in abdominal region (P&lt;0.01). The indentation work load was lowest in the thigh (P&lt;0.001). The total mechanical work load was highest in the deltoid region and lowest in the abdominal region (P&lt;0.001). The occurrence of bleeding from the needle insertions was lowest in the abdominal region (P=0.01). The occurrence of pain and the pain quality from needle insertions did not differ between the anatomical regions. However, the intensity of pain in the needle insertions reported to be painful was lowest in the deltoid region (P&lt;0.01). Positive relations between higher mechanical parameters of insertions with 30G needles and the occurrence of pain were demonstrated. Higher total mechanical work load was related to increased pain intensity. Ultrasonographically, the thickness of the epidermal entrance echo was highest in the thigh (P&lt;0.001), and the thickness of both the dermal echo and the total skin echo thickness were highest in the abdominal region (P&lt;0.001). The mean ultrasonographic density of the dermal echo was lowest in the abdominal region and highest in the thigh (P&lt;0.001). The thickness of the dermal echo, of the total skin echo and the dermal echo density were all significantly inversely related to the indentation work load (P&lt;0.001).Conclusions: Specific mechanical parameters of needle insertions could be demonstrated in different anatomical regions. Differences in pain perception from needle insertions in different anatomical regions were not reflected by occurrence of pain but by pain intensity, with the lowest pain intensity registered in the deltoid region. Ultrasonographically, increased skin thickness and decreased density of the dermal echo were related to lower indentation work load during the needle insertions.

Pain and mechanical injury of human skin following needle insertions

Needle insertion is a very common invasive procedure, but little has been done to study how pain is related to the mechanical properties of the needle insertion, and how pain from the procedure may be minimized. The aim of the present study was to investigate the pain evoked by standardized needle insertion into the human skin. Needle insertions were performed with continuous registration of the mechanical force on the needle. Forty consecutive needle insertions to the depth of 8 mm with 27G and 30G needles, 2 and 19 mm/s velocities, and at 45 and 90 degree angles to the skin surface were performed in a randomized and blinded design in 30 healthy volunteers. The occurrence, intensity and quality of pain, as well as the maximum mechanical needle penetration force and the total mechanical workload were registered. The mechanical parameters of needle insertions were significantly related to needle size and velocity of insertion. Occurrence of pain and bleeding were significantly related to the needle size. High needle insertion velocity was significantly related to a higher rate of sharp and pricking pain, and low insertion velocity to a significantly higher rate of dull and burning pain. The present study provides quantitative data on pain and mechanical parameters of standardized needle insertions through normal human skin.