Personal Attenuation Rating Research Articles

Association between personal attenuation rating with types of earplugs and noise exposure levels in a textile factory in China

Objective To investigate the effects of earplug type and noise exposure level on textile workers' personal attenuation rating (PAR). Design Initial and follow-up visits were conducted at a 17-month interval. At each visit, a baseline HPD fit test was performed using either a 3M foam or pre-molded earplug, as chosen by the workers. Workers who failed to meet targeted levels were trained and retested. Once they failed again, the other earplug was selected, and training was provided until they achieved the PAR target. Study sample 192 textile workers into three noise exposure level groups (low, medium, high). Results The median baseline PAR was 10 dB at the initial visits and 13 dB at the follow-up visits, and obtained by foam earplug users was 20 dB, which was higher than that obtained by pre-molded earplug users [12 dB (95% CI, 10–15 dB)]. The highest median baseline PAR was obtained by the high noise level group, followed by the median and low noise level groups. Training significantly increased the PAR. Conclusions Multiple types of earplugs need to be offered to workers to deal with individual differences in attenuation, preferences, and exposure levels. Training and stricter compliance policies can improve HPD use and fitting, contributing to better hearing health.

Measurement and evaluation of personal attenuation rating before and after the training of the noise-exposed workers wearing foam earplugs

Objective: To measure and compare the difference of personal attenuation rating (PAR) of the workers wearing foam earplugs before and after the training, and to evaluate the effect of ear protector wearing training on the noise protection. Methods: In February 2023, 94 workers exposed to noise in a machinery manufacturing factory were selected as subjects. The production noise in the workplace was measured and subjects were trained to wear earplugs. The PAR values of wearing 3M 1110 foam test earplugs were measured and recorded before and after the training by using the fit testing of hearing protection device. The differences between the actual PAR values with nominal values and the noise attenuation values in related standards were compared, and the protective effect of hearing protection device before and after training was evaluated. Results: The average age of the subjects was (36.76±11.48) years old, the average length of service was (16.34±11.64) years, and the average exposure time to noise was (15.67±11.64) years. The noise detection results of the subjects' posts were ranged from 80.1 to 94.3 dB (A). The results of subjects wore 3M 1110 foam test earplugs for fit testing showed that the binaural PAR value after training was (19.3±6.4) dB (A), which was significantly higher than that before training (11.1±7.4) dB (A) (t=13.31, P<0.001). After training, 11 people (11.70%) could reach the corrected noise reduction value (NRR value), 26 people (27.66%) could reach the standard of single noise reduction value (SNR value) ×0.6, and 84 people (89.36%) could reach the standard of (NRR-7) /2. The under protection rate of hearing protectors after training (7.45%) was significantly lower than that before training (45.74%), and the difference of different protection levels before and after training was statistically significant (χ(2)=40.83, P<0.001) . Conclusion: It is suggested that enterprises should use the fit testing instead of nominal value estimation to evaluate the noise reduction effect of hearing protection device. Special training on the selection and use of hearing protection device should be strengthened, so as to ensure that workers wear them correctly and improve the protective effect of hearing protection device.

A study on the hearing protection and intervention effects of silicone earplug usage among manufacturing workers

Objective: To assess the efficacy of silicone earplugs in protecting workers exposed to noise in a typical manufacturing environment, and to provide training interventions for workers who do not achieve the anticipated noise reduction levels, as well as examining the spectral characteristics of earplug attenuation. Methods: From June to August 2022, a total of 294 noise-exposed workers in two manufacturing enterprises equipped with the same type of earplug were studied by cluster sampling method, by conducting questionnaire surveys, collecting data, fitting tests, and providing trainings, the current noise exposure levels of workers in the industry as well as the perception about the earplug were understood. Additionally, the attenuation before and after intervention in workplace were measured, the spectral characteristics of noise reduction were were described and compared. Results: The percentage of workers with Personal Attenuation Rating (PAR) of 0 is 32.7% (96/294), and the baseline pass rates are all below 60%. There were no significant differences in pass rates based on gender, age, noise exposure, education level, or cognition of earplug effectiveness. After adjusting the way that earplugs are worn or changing the type of earplugs, all workers were able to meet their noise reduction requirements. The median PAR improvement for both companies is above 10 dB. The noise attenuation of the earplug vary with frequency, with lower attenuation at 4 000 Hz and higher attenuation at 8 000 Hz, showing some deviation from the nominal values. Conclusion: The difference between the actual sound attenuation value of earplugs and the nominal value is related to the noise frequency. When using silicone earplugs, attention should be paid to the spectral composition of the noise in the workplace.

Evaluating Earplug Performance over a 2-Hour Work Period with a Fit-Test System.

Workers rely on hearing protection devices to prevent occupational noise-induced hearing loss. This study aimed to evaluate changes in attenuation over time for properly fit devices when worn by workers exposed to hazardous noise. Earplug fit testing was accomplished on 30 workers at a brewery facility with three types of foam and three types of premolded earplugs. The personal attenuation ratings (PARs) were measured before and after a 2-hour work period while exposed to hazardous noise levels. The minimum acceptable initial PAR was 15 dB. Average decreases in PAR ranged from -0.7 to -2.6 dB across all six earplug types. Significant changes in PAR were observed for the Foam-1 ( p = 0.009) and Premold-3 ( p = 0.004) earplugs. A linear mixed regression model using HPD type and study year as fixed effects and subject as random effect was not significant for either fixed effect ( α = 0.05). Ninety-five percent of the final PAR measurements maintained the target attenuation of 15 dB. Properly fitting earplugs can be effective at reducing worker's noise exposures over time. The potential for a decrease in attenuation during the work shift should be considered when training workers and establishing the adequacy of protection from hazardous noise exposures.

Risk assessment on noise-induced hearing loss of 488 workers in a petrochemical plant

Objective: To assess the risk of noise-induced hearing loss in workers from a petrochemical plant. Methods: In October 2020, 488 male workers exposed to noise in a petrochemical plant in Guangdong Province were selected by cluster sampling. Acoustics-Estimation of Noise-Induced Hearing Loss (ISO 1999: 2013) was used to assess the risk of noise-induced hearing loss of workers, and individual fit testing was used to evaluate the sound attenuation obtained by the workers. The risk assessment results and fitness test results of workers with different hearing levels were compared. Results: The average noise exposure equivalent sound level of the workers in the petrochemical plant was 86.7 dB (A) . The median of PARs (personal attenuation ratings) was 16 (4, 23) dB. There were statistically significant differences in age and service years among workers with different hearing results (P<0.05) , but no statistically significant differences in noise intensity and PARs (P>0.05) . According to risk assessment results of ISO 1999: 2013, the current risk of high-frequency hearing loss in 488 workers were negligible risk and acceptable risk. The risk of noise-induced deafness weredivided into three levels: negligible risk in 452 workers (92.7%) , medium risk in 27 workers (5.5%) and high risk in 9 workers (1.8%) . The risk of high-frequency hearing loss in next 5 to 15 years for workers with noise exposure level of >94 to 97 dB and >97 dB or above would be medium risk or above. The risk of noise-induced deafness in next 5 to 15 years for workers exposed to noise withlevel of 91 to 94 dB would be medium risk or above. Conclusion: The risk of noise-induced hearing loss in workers from the petrochemical plant is high in next 5 to 15 years, and noise prevention and control measures need to be strengthened. ISO1999: 2013 assessment method may underestimate the risk of hearing loss among workers.

Personal attenuation ratings versus derated noise reduction ratings for hearing protection devices.

National and international regulatory and consensus standards setting bodies have previously proposed derating hearing protector ratings to provide a better match between ratings determined in a laboratory and the real-world measurements of attenuation for workers. The National Institute for Occupational Safety and Health has proposed a derating scheme that depends upon the type of protector. This paper examines four real-world studies where personal attenuation ratings (PARs) were measured at least twice, before and after an intervention in earplug fitting techniques. Results from these studies indicate that individualized earplug fitting training dramatically improves a worker's achieved PAR value. Additionally, derating schemes fail to accurately predict the majority of achieved PARs. Because hearing protector fit testing systems are now readily available for use in the workplace, personal attenuation ratings provide a better estimate of worker noise exposures and are able to identify those persons who need additional instruction in fitting hearing protection devices.

Using a boothless audiometer to estimate personal attenuation rating in a military hearing conservation clinic.

Hearing protection device (HPD) fit-testing is considered "best practice" for hearing conservation programs in the military. Yet many hearing conservation personnel do not have access to dedicated fit-test equipment. In this study, estimates of personal attenuation rating (PAR) obtained with a boothless audiometer are compared to those obtained with a field-microphone in a real ear (F-MIRE) system. Results suggest that boothless audiometers can be used to make accurate PAR estimates. The ability to perform HPD fit-testing with multipurpose boothless audiometers has the potential to greatly expand the accessibility of earplug verification and ultimately to improve the effectiveness of hearing conservation programs.

Evaluation of hearing protection device effectiveness for musicians

Objective To evaluate musicians’ personal attenuation and perceptions of three types of hearing protection devices (HPDs): formable foam earplugs and both non-custom and custom versions of uniform attenuation earplugs (UAEs) marketed to musicians. Design A mixed-methods approach was used to evaluate the HPDs. Audiometric testing obtained hearing levels at baseline and with each HPD across frequencies (125–8000 Hz) to determine personal attenuation ratings and uniformity of attenuation. Participants completed surveys over six months regarding how often they used the HPDs and their perceptions about wearing them. Study sample Twenty-four musicians were recruited to participate. Results Substantial variability was observed in the attenuation achieved among participants for each HPD type, but custom UAEs provided the most consistent attenuation across frequencies. Participants’ HPD preferences were influenced by multiple factors including personal instrument and specific activity. Custom UAEs were most frequently used but usage rates continually decreased over the 6-month period. Conclusions Fit-testing is important to determine fit and sizing. Combining information on the effectiveness of HPDs with musicians’ opinions about wearing them can inform recommendations for which types may be the most effective and feasible options for reducing sound exposures.

The efficacy of earplugs at a major hazard facility.

At a major hazard facility, cases of occupational noise-induced hearing loss have occurred despite the use of hearing protection devices. Preliminary measurements of personal attenuation ratings (PAR) suggested that earplugs may not achieve the attenuation implied by their Australian SLC80 Class designation in field-use conditions. We examined the relationship between PAR and the SLC80 classification for earplugs, as a good understanding of the attenuation provided by earplugs under normal field-use conditions, rather than in laboratory settings, is vital to their effective use as a control measure for noise exposure. A cross-sectional study was performed with 65 volunteers. Participants were recruited from Operations and Maintenance Technicians at the major hazard facility. The participants had their PARs checked with different earplug types using the 3M™ E-A-Rfit™ system. We examined the PARs measured and also assigned a 'pass' or 'fail' rating depending on whether the earplug achieved 22dB attenuation. 22dB attenuation for 80% of users is the minimum to meet the definition for Australian SLC80 Class 4 hearing protection. None of the earplug types achieved 22dB attenuation for 80% of users when tested in field-use conditions. There were statistically significant differences in the frequency of achieving a 'Pass', and in PAR, depending on earplug type. Roll-down foam earplugs may provide superior attenuation compared to pre-moulded earplugs. Earplugs are unlikely to achieve the attenuation found in laboratory conditions during field-use. Personalised selection of hearing protection devices based on fit-testing results should be encouraged.

Verifying earplug attenuation and evaluating the effectiveness of one-on-one training along with earplug fit testing at nine facilities in China.

The purpose of this study was twofold: (1) to measure the personal attenuation ratings (PARs) in Chinese workers wearing hearing protection devices (HPDs), to evaluate the effectiveness of the single number rating (SNR), the noise reduction rating (NRR), and the associated derated values of earplugs; and (2) to evaluate the effectiveness of one-on-one training along with earplug fit testing on PAR improvement. Noise exposure measurements, one-on-one training, and fit tests to measure earplug attenuation were conducted at nine manufacturing facilities located in eastern China from 2016 to 2017. 503 workers participated in the study. Ninety-three percent were male. 199 workers were provided one-on-one training. Before training, 14% and 15% of the workers achieved the attenuation predicted by the manufacturer's SNR and NRR, 56% and 65% exceeded the derated SNR and NRR, respectively. Following one-on-one training, mean PAR improved significantly by 15 dB (p < 0.01); 26% of the workers achieved SNR and NRR, 79% and 91% met the associated derated values, respectively. Labeled noise attenuation ratings and their derated values overestimated the actual level of attenuation among workers wearing HPDs. One-on-one training along with earplug fit testing contributed to improved PARs.

Evaluating the Effectiveness of Earplugs in Preventing Noise-Induced Hearing Loss in an Auto Parts Factory in China.

A survey was administered to 385 noise-exposed workers from an auto parts factory and 1268 non-noise-exposed health department employees in China. Individual 8 h A-weighted equivalent sound levels (LAeq,8h), earplug personal attenuation ratings (PARs), and pure-tone audiometric tests were performed. The average LAeq,8h of noise-exposed workers was 87 dB (A) with a mean PAR of 7 dB. The prevalence of high-frequency hearing loss was 65% for noise-exposed workers and 33% for the non-noise-exposed employees. The use of earplugs had no observable effect on the prevalence of high-frequency hearing loss of the study participants (OR 0.964, 95% CI 0.925–1.005, p = 0.085). No significant relationship between the effectiveness offered by earplug use and high-frequency hearing thresholds at 3, 4, and 6 kHz was found (t = −1.54, p = 0.125). The mandatory requirement of earplug use without individualized training on how to wear HPDs correctly had no detectable effect on the prevention of hearing loss at the auto parts factory. The hearing conservation program at the surveyed factory was not effective. Periodic hearing tests, earplug fit testing, expanding the offer of different types of hearing protection, and employee education about the importance of protecting their hearing were recommended to the occupational health and safety program.

Hearing loss as a predictor for hearing protection attenuation among miners

ObjectiveThis study investigated risk factors for poor earplug fit, with a focus on the association between hearing loss and personal attenuation ratings (PARs).MethodsEarplug fit was assessed by obtaining PARs using...

Field Attenuation of Foam Earplugs.

BackgroundHearing protection devices (HPDs) are often used in the workplace to prevent hearing damage caused by noise. However, a factor that can lead to hearing loss in the workplace is improper HPD fitting, and the previous literature has shown that instructing workers on how to properly insert their HPDs can make a significant difference in the degree of attenuation.MethodsTwo studies were completed on a total of 33 Hydro One workers. A FitCheck Solo field attenuation estimation system was used to measure the personal attenuation rating (PAR) before and after providing one-on-one fitting instructions. In addition, external ear canal diameters were measured, and a questionnaire with items related to frequency of use, confidence, and discomfort was administered.ResultsTraining led to an improvement in HPD attenuation, particularly for participants with poorer PARs before training. The questionnaire results indicated that much HPD discomfort is caused by heat, humidity, and communication difficulties. External ear canal asymmetry did not appear to significantly influence the measured PAR.ConclusionIn accordance with the previous literature, our studies suggest that one-on-one instruction is an effective training method for HPD use. Addressing discomfort issues from heat, humidity, and communication issues could help to improve the use of HPDs in the workplace. Further research into the effects of canal asymmetry on the PAR is needed.

How hearing conservation training format impacts personal attenuation ratings in U.S. Marine Corps Training Recruits

Objective The purpose of this fit-testing study in the field was to systematically compare three Hearing Protection Device (HPD) fit-training methods and determine whether they differ in the acquisition of HPD fitting skill and resulting amount of earplug attenuation. Design Subjects were randomly assigned to receive HPD fit-training using one of three training methods: current, experiential HPD (eHPD), and integrated. Personal Attenuation Ratings (PARs) were acquired via HPD fit-testing and used to verify attenuations pre- and post-training. Study Sample US Marine training recruits (n = 341) identified via HPD fit-testing for remedial HPD fit-training and assigned to three cohorts. Results The post-training HPD fit-test passing rate differed by training method, with pass rates ranging from 50% (current) to nearly 92% (eHPD). The difference between group delta PAR values were significantly higher (>9 dB) in both the eHPD and integrated methods compared to the current method. Conclusion The HPD fit-training methods that teach “what right feels like” (eHPD and integrated) provided a greater number of trainees with the skill to achieve noise attenuation values required for impulse noise exposures encountered during basic training. The attenuation achieved by those methods was significantly greater than the current training method.

Evaluating the Effect of Training Along With Fit Testing on Premolded Earplug Users in a Chinese Petrochemical Plant.

To gain insight into the current practice of hearing protection of Chinese workers and the value of hearing protection device (HPD) fit testing. HPD fit testing was conducted on workers (N = 774) in a petrochemical plant in Eastern China who were on duty during the period of this study. The 3M E-A-Rfit Dual-Ear Validation System was used to measure the personal attenuation ratings (PARs) of a premolded earplug used at the work site. Repeated fit testing was conducted at approximately 6- or 12-month intervals. Wilcoxon signed rank tests were conducted to analyze the pairwise differences between the baseline, postintervention, and follow-up visit PARs, and Mann-Whitney tests were used to compare the PARs obtained by two follow-up groups. The median PAR baseline was 11 dB; significant improvement was shown on the postintervention PARs (p < 0. 001). No significant difference was shown between PARs obtained during the 6- and 12-month follow-up visits (p > 0.05). Comparing PARs of follow-up visits with the baseline PAR demonstrated a significant improvement (p < 0. 001), but revealed a significant decline (p < 0. 001) comparing with the postintervention PARs. HPD fit testing showed value added as to verify the sufficiency of attenuation. The training along with fit testing showed contributions to improve PARs, maintained effectiveness over time, and assisted in HPD selection. Follow-up is believed to be important to ensure that the HPDs are continually used correctly. There was no significant difference in the sustained effectiveness of the follow-up when observe 6- and 12-month subsequent to intervention.

Individual Fit Testing of Hearing-Protection Devices Based on Microphones in Real Ears among Workers in Industries with High-Noise-Level Manufacturing.

Hearing-protection devices (HPDs) are particularly important in protecting the hearing of workers. The aim of this study was to prevent hearing damage in workplaces in Taiwan. It was conducted to determine the actual sound attenuation of the personal attenuation rating (PAR) values when wearing HPDs via measurements from field microphones in workers’ real ears (F-MIRE). Across 105 measurement trials for the Classic™ roll-down foam earplug HPDs worn by the workers, there were 23 cases of ineffective protection (including caution and fail); the proportion was 20% (including the first measurement and re-wear of HPDs after education and training). In addition, re-education and training in how to wear the HPDs was provided, improving wearing skills. A total of 29 testees wearing the Classic™ roll-down foam earplug HPDs failed to meet the pass standard for the first PAR test, and 6 of them improved and subsequently passed the PAR test. The improvement rate was 20%. These 23 testees switched to another HPD, namely Kneading-Free Push-Ins™ earplugs. From this group, 16 effective sound attenuation values were obtained, with an improvement rate of 70%. However, seven testees failed to pass the PAR test, and after education, training, and replacement of HPDs with different types, they still could not pass the PAR test. At that time, even if the UltraFit™ pre-molded earplugs were adopted again for wear and replacement, they were still unable to pass the PAR test. This HPD was eventually replaced with the PELTOR X4A Earmuff HPD and then tested again, with these HPDs finally passing the PAR test. In Taiwan, the use of fit testing has been increasing but it is not a common practice, and few studies on hearing-protection fit testing have been conducted in this country. The goal of this study was to gain more insight into the current hearing protection situation, including field attenuation of HPDs obtained by workers, the effects of training on improving the attenuation of HPDs after F-MIRE measurements, and the awareness of hearing health and motivation on the use of HPDs in a high-noise-level environment.

Training in the proper use of earplugs: An objective evaluation.

Discrepancies between attenuation obtained in the laboratory and the field are caused by several factors associated with hearing protection devices (HPDs). The effects of some factors can be minimized with proper training provided to HPD users. To evaluate the effectiveness of an educational intervention for improving the correct use of earplugs as HPDs in workers exposed to occupational noise by using the F-MIRE method and by comparing pre- and post-training attenuation values and pass/fail rates. The personal attenuation ratings (PARs) of two types of earplugs were obtained (140 individuals) using E-A-Rfit™ equipment. Each HPD was evaluated under two scenarios: first after the user only read the packaging instructions, and then after the user read guidelines and participated in a training program. The results obtained were automatically classified by the software as "Approved" or "Failed". There was a significant post-training increase in the binaural PAR values for both HPDs. The percentages of passes pre- and post-training showed that training users in the proper fit of the HPD was effective; both types had statistically significant differences. This study found a statistically significant increase in PARs and the number of workers passing evaluations after HPD fit training, demonstrating the effectiveness of this educational intervention.

Hearing Protector Attenuation and Noise Exposure Among Metal Manufacturing Workers.

This study utilized personal noise measurements and fit-testing to evaluate the association between noise exposures and personal attenuation rating (PAR) values among participating workers, and second, to compare the attenuated exposure levels received by the workers and the British Standards Institute's recommended noise exposure range of 70 to 80 dBA. We measured hearing protection device (HPD) attenuation among a sample of 91 workers at 2 US metal manufacturing facilities, through performance of personal noise dosimetry measurements and HPD fit-testing over multiple work shifts. We compared this testing with participant questionnaires and annual audiometric hearing threshold results. The average 8-hr time-weighted average noise exposures for study participants was 79.8 dBA (SD = 7.0 dBA), and the average PAR from fit-testing was 20.1 dB (±6.7 dB). While differences existed between sites, 84% of the 251 PAR measurements resulted in effective protection levels below the recommended 70 dBA (indicating overprotection), while workers were underprotected (i.e., effective exposures >80 dBA) during <1% of monitored shifts. Our results also demonstrated a significant positive relationship between measured noise exposure and PAR among non-custom-molded plug users (p = 0.04). Non-custom-molded plug wearers also showed a significant increase in PAR by sequential fit-test interaction (p = 0.01), where on average, subsequent fit-testing resulted in increasingly higher HPD attenuation. Workers at site 1 showed higher PARs. PARs were significantly related to race, even when adjusting for site location. While age, hearing threshold level, task, and self-reported tinnitus showed no significant effect on individual PAR in an unadjusted model, site, race, and sand- or water-blasting activities were significant predictors in adjusted models. Within-worker variability in time-weighted averages and PARs across repeated measurements was substantially lower than variability between workers. Careful selection of HPDs is necessary to minimize instances of overprotection to workers in low and moderate occupational noise environments. The use of fit-testing in hearing conservation programs to evaluate PAR is recommended to avoid overprotection from noise exposure while also minimizing instances of under-attenuation.

Evaluating the effect of training along with fit testing on foam earplug users in four factories in China

Objectives: To gain insight into the hearing protection practice of Chinese workers and the value of hearing protection fit testing.Design: The Field Attenuation Estimation System (FAES) was used to measure the personal attenuation ratings (PARs) of one foam earplug used at the work sites in China. Intervention was provided to workers who needed it. Follow-up fit testing was conducted approximately six months later. Paired t-tests were conducted to compare the baseline, post-intervention and follow-up visit PARs.Study sample: Fit testing was conducted on 335 workers in four factories with 269 workers intervened. Follow-up visit was conducted on 97 intervened workers in three factories.Results: The mean PAR baseline was 10 dB. Significant improvement was shown on post-intervention PARs (p < 0.05) as well as follow-up visit PARs (p < 0.05). Comparing follow-up visit PARs to post-intervention PARs, good sustainability was shown in two factories (p > 0.05), while a significant decline (p < 0.05) was observed in another.Conclusions: Hearing protection fit testing demonstrated value for verifying sufficiency of attenuation. The training along with fit testing contributed to improve PARs and maintaining effectiveness over time. Employer’s attention and follow-up actions are important in sustaining the training effectiveness.

The effect of earplug training on noise protection.

BackgroundNoise-induced hearing loss is an occupational disease, and workplace noise exposure is a major hazard in Korea. Although hearing protectors effectively reduce a worker's exposure to noise, their success is compromised by the wearer's inability to fit the protectors correctly, and there are no proper training methods for using hearing protectors in small-scale industries. This study aims to evaluate the effect of earplug training on hearing protection using field microphone-in-real-ear (F-MIRE) and prevent noise-induced hearing loss.MethodsThe study population comprised 172 noise-exposed manufacturing workers who visited occupational health facilities in Daegu, South Korea, between July 2014 and September 2017. Personal attenuation ratings (PARs) were calculated with F-MIRE. Paired t-tests were used to compare the differences in PAR (dB) before and after training, and generalized estimating equations (GEEs) were used to compare the differences in PAR according to the number of trainings.ResultsMean PARs increased after the first and second training, and the differences were statistically significant. Among the 30 participants who received all 4 trainings, PARs were significantly higher after each training than before the training. As the number of training increased, the differences in PARs significantly increased. When comparing pretraining PARs for each training session, we found statistically significant differences between the first and second training and between the second and third training, but not between the third and fourth training.ConclusionIn this study, the short- and long-term effects of earplug training were statistically significant. In particular, the PAR before and after the fourth training showed the greatest increase, and the PARs continued to increase during each training.