Computer-Based Estimation of Spine Loading during Self-Contained Breathing Apparatus Carriage

Firefighters’low back disorders(LBDs)are closely related to excessive spine loading when using the self-contained breathing apparatus(SCBA)continuously.The purpose of this study was to quantify firefighters’spine loading and evaluate the effects of strap lengths of SCBA on altering spine loading.Computer-based musculoskeletal models of three varying-strapped SCBA conditions and a control condition(CC)with no SCBA equipped were developed.The model was driven using three-dimensional(3 D)inertial motion capture data from twelve male subjects performing a walking task and the predicted ground reaction force(GRF).Electromyography(EMG)activities were also recorded to validate the results from the model.The 4 th-5 th lumbar vertebra(L4/L5)joint reaction forces,as well as erector spinae and rectus abdominis forces,were finally obtained.Results demonstrated that carrying SCBA significantly increased the compressive force and anteroposterior shear force at the spine.The risk of potential LBDs increased by about 17.77%.Dynamic balance of erector spinae and rectus abdominis contraction was also disturbed when carrying SCBA,indicating a higher risk of spine muscle strain.Adjustment of SCBA strap length was an efficient method to influence spine loading.The medium-fitting strap(MS)with a length of around 101 cm generated minimum joint reaction forces and achieved the optimum dynamic balance of spine muscle contraction,which was recommended for firefighters.

Effect of Respirator Resistance on Tolerant Capacity during Graded Load Exercise

Respirator breathing resistance impacts performance of wearers during constant work load. However, it is less clear as to how breathing resistance affects the tolerant capacity of users during graded work load. The present study investigated the tolerant capacity of 8 individuals during incremental work load. The 8 subjects were required to wear two matched respirators （respirators Ⅰ and Ⅱ which were designed to have different breathing resistances and the same dead space） respectively on separate days and then work to end points. Minute ventilation （VE）, breathing frequency （BF）, oxygen consumption （VO2） and heart rate （HR） were recorded during exercise, while tolerant time, response time and breathing discomfort were measured at the end of each test trial. The test variables were com-pared between the two respirators by using matched-pairs t-test. The results showed that the tolerant time was significantly reduced for the respiratorⅠwith higher level of breathing resistance when compared with its counterpart with lower breathing resistance （respirator Ⅱ） （P〈0.05）. The same changes occurred for response time. Results also showed a significant increase in VE and BF for respirator Ⅰwearers when the work load was above 125 W. The O2 consumption was similar under the two breathing resistance conditions. These findings suggested that the respiratory resistance caused by self-contained breathing apparatus （SCBA） has an impact on the tolerant capacity of users.