| BackgroundThe decline in muscle mass and strength,as a common health problem in older adults,can progress at a rapid rate and pose a significant health risk to the older adults.Resistance training/exercise is effective in slowing down or even reversing the loss of muscle mass and strength,and has many advantages such as being economical and convenient.The benefits and safety of exercise depend on the scientific and suitable exercise program,and in which the appropriate resistance training load is the most important part.However,the method of developing the appropriate resistance training load has not received extensive attention,and the currently available methods contain some disadvantages such as complexity,high professional requirements,time consumption and poor generalizability.It has been found that some simple muscle strength indicators,which are commonly used in the older adults with the strengths of being inexpensive and accurate,are possibly correlated with the appropriate load of resistance training.This relationship provides the possibility of evaluating resistance training load by measuring simple muscle strength indicators,thus simplifying the determination process for resistance training load in older adults.However,the relationship is still unknown in Chinese older adults.Additionally,the relationship between different resistance movements and different muscle strength indicators are unclear.ObjectivesThe main purpose of this study was to explore the correlation between the simple muscle strength indicators and the appropriate loads of resistance training in the older adults.Based on the correlation,the estimation formulas of the appropriate load of resistance training were constructed.With this study,we aimed to simplify the determination process for resistance training load,which constitutes the most difficult and critical elements in resistance training.The results were expected to facilitate the formulation of resistance exercise prescriptions by medical and nursing personnel as well as the older adults themselves,and to boost the scientific resistance training in the older adults in China,thereby improve the health level in older adults and promote healthy aging.MethodThis is a cross-sectional study which containing two parts:determination of resistance training movements and indicator measurement.Part I:Based on the available literature,our own experience,and the discussion in the research group,resistance training movements for testing was preliminarily selected.A convenience sampling method was applied to select the older adults for a 610 days pre-application in June 2022 with the purpose for determination of the resistance training movements.Part II:Older adults were recruited through convenience sampling method in Senior Care Facilities from June to December 2022.Before formal test,all subjects underwent adaptive training for 6～10 days,with the main purpose of learning resistance training movements and familiarizing with measurement scales to ensure the safety and accuracy of measurements.The indicators included simple muscle strength indicators and suitable loads of resistance exercise movements.According to the determined resistance exercise movements and related literature,the selected simple muscle strength indicators are listed as follows:(1)upper limb muscle strength indicators,including 30-second biceps curl and handgrip strength;(2)lower limb muscle strength indicators,including 30second sit-and-stand,five times sit-to-stand,knee extensor muscle strength and knee flexor muscle strength.Measuring the suitable load of final determined resistance exercise movements.In measurement,the subjects were required to repeat the movement for 12 times(1 set)under the initial load.Rating of Perceived Exertion(RPE)and Repetitions in Reserve(RiR)were measured and accordingly the load was adjusted.Participants were asked to complete the same process again after 3-5 minutes of rest until RPE and RiR met the requirements.The test in each movement should be controlled within 4 sets in one day.If the appropriate load was not determined within 4 groups,the test would be repeated after 48 hours.Pearson or Spearman correlation analysis was used to analyze the correlation between the simple muscle strength parameters and the appropriate loads of resistance training.Multiple linear regression was applied to establish the estimation formulas for the appropriate loads of resistance training.The validity of the estimation formulas was evaluated by the within-sample back substitution test and the consistency between the results of the estimation formula and the actual measured values was tested with BlandAltman analysis.ResultPhase ⅠA total of 14 subjects completed the pre-application.The final resistance training movements were determined to include elbow flexion and extension with horizontally straightened arms(below simplified as elbow flexion and extension),shoulder press,seated knee extension,and standing straight leg backward raise.Phase ⅡA total of 156 subjects were recruited,and after screening with the inclusion and exclusion criteria,a total of 128 subjects were qualified to accept the adaptive training.A total of 37 cases dropped out during the adaptation training,and a total of 91 subjects[including 27(29.7%)males and 64(70.3%)females]finally completed all the measurements.1 Results of correlation analysis1.1 Upper limbs resistance training1.1.1 Elbow flexion and extensionThe load of elbow flexion and extension was significantly and positively correlated with both the 30-second biceps curl and handgrip strength,a result that remained consistent across overall,male,and female subjects(P<0.05).The correlation coefficient of the 30-second biceps curl was highest in males(r=0.568)and of the handgrip strength was highest in the overall population(r=0.667).1.1.2 Shoulder pressThe load of shoulder press was significantly and positively correlated with both the 30-second biceps curl and handgrip strength,a result that remained consistent across overall,male,and female subjects(P<0.05).The correlation coefficient of the 30second biceps curl was highest in males(r=0.625)and the correlation coefficient of handgrip strength was highest in the overall population(r=0.601).1.2 Lower limbs resistance training1.2.1 Seated knee extensionThe load of seated knee extension was significantly and positively correlated with the 30-second sit-and-stand in overall and male subjects(P<0.05),significantly and negatively correlated with five times sit-to-stand in male subjects(P<0.05),and significantly and positively correlated with knee extensor muscle strength in overall,male,and female subjects(P<0.05)with the highest correlation coefficient in male subjects(r=0.634).There was no significant correlation with knee flexor muscle strength(P>0.05).1.2.2 Standing straight leg backward raiseThe load of standing straight leg backward raise was significantly and positively correlated with the 30-second sit-and-stand in overall and male subjects(P<0.05),significantly negatively correlated with five times sit-to-stand in male subjects(P<0.01),and significantly and positively correlated with knee extensor muscle strength in overall,male,and female subjects(P<0.05),with the highest correlation coefficient in male subjects(r=0.639),and significantly and positively correlated with knee flexor muscle strength in overall and male subjects(P<0.05).2 Results of linear regression analysis2.1 Upper limbs resistance training2.1.1 Elbow flexion and extensionThe handgrip strength was significantly associated with the load of elbow flexion and extension(P<0.01),and the goodness of fit for the regression equation was 44.5%.The estimation formula for the load of elbow flexion and extension was as follows:the load of elbow flexion and extension(kg)=0.376+0.108*handgrip strength(kg).2.1.2 Shoulder pressThe handgrip strength was a significant influence on the load of shoulder press(P<0.01),and the goodness fit of the regression equation was 36.1%.The estimation formula for the load of shoulder press was as follows:the load of shoulder press(kg)=0.542+0.094*handgrip strength(kg).2.2 Lower limbs resistance training2.2.1 Seated knee extensionKnee extensor muscle strength,physical activity or not,and length of residence in the Senior Care Facilities were significant influences on the load of seated knee extension(P<0.01),and the goodness fit of the regression equation was 34.7%.The estimation formula for the load of seated knee extension was as follows:the load of seated knee extension(kg)=3.984+0.178*knee extensor muscle strength(kg)-0.993*physical activity or not-0.664*length of residence in the Senior Care Facilities(years).2.2.2 Standing straight leg backward raiseKnee extensor muscle strength,length of residence in the Senior Care Facilities and regular exercise or not were significant influences on the load of standing straight leg backward raise(P<0.01),and the goodness fit of the regression equation was 35.3%.The estimation formula for the the load of standing straight leg backward raise was as follows:the load of standing straight leg backward raise(kg)=3.957+0.161*knee extensor muscle strength(kg)-0.921*length of residence in the Senior Care Facilities(years)+ 0.831*whether regular exercise or not.3 Result of the within-sample back substitution testThe data of all subjects were substituted into the estimation formulas to obtain the estimated values of appropriate loads for all moverments.The results showed that the differences between the estimated and measured values were not statistically significant(P>0.05),and there was a significant positive correlation between the estimated and measured values(P<0.01).4 Result of Bland-Altman consistency analysis4.1 Upper limbs resistance training4.1.1 Elbow flexion and extensionThe mean value of the difference between the estimated and measured load of elbow flexion and extension was-0.0072 kg,and the 95%limits of agreement were1.21～1.21 kg,with a total of 97.8%of the points distributed within 95%limits of agreement.The minimum value of the difference within the limits was-1.20 kg,which absolute value accounted for 39.4%of the mean value of the measured load of elbow flexion and extension.4.1.2 Shoulder pressThe mean value of the difference between the estimated and measured load ofshoulder press was-0.0152 kg,and the 95%limits of agreement were-1.28～1.25 kg,with a total of 96.7%of the points distributed within 95%limits of agreement.The maximum value of the difference within the limits was 1.21 kg,which accounted for 43.0%of the mean value of the measured load of shoulder press.4.2 Lower limbs resistance training4.2.1 Seated knee extensionThe mean value of the difference between the estimated and measured load of seated knee extension was-0.0793 kg,and the 95%limits of agreement were3.18～3.18 kg,with a total of 93.4%of the points distributed within 95%limits of agreement.The maximum value of the difference within the limits was 3.02kg,which accounted for 52.8%of the mean value of the measured load of seated knee extension.4.2.2 Standing straight leg backward raiseThe mean value of the difference between the estimated and measured load of standing straight leg backward raise was 0.027 kg,and the 95%limits of agreement were-3.02～3.07 kg,with a total of 94.5%of the points distributed within 95%limits of agreement.The maximum value of the difference within the limits was 2.91 kg,which accounted for 49.3%of the mean value of the measured load of standing straight leg backward raise.Conclusion1.In this study,the appropriate loads of resistance exercise movements in the older adults correlated well with the simple muscle strength levels.The appropriate load for upper limbs resistance exercise movements has the strongest correlation with handgrip strength,and the appropriate load for lower limbs resistance training movements has the strongest correlation with knee extensor muscle strength.2.Based on the strong correlation between the appropriate loads of upper and lower limb resistance training movements and handgrip strength and knee extensor muscle strength,respectively,four estimation formulas of appropriate loads of resistance training movements were established.3.The within-sample back substitution test showed good validity of the estimation formulas for appropriate loads of the four resistance training movements.4.The consistency analysis showed that the estimated values derived from the appropriate load estimation formulas of the four resistance exercise movements were in fair agreement with the measured values,with a slightly better agreement in the upper limbs resistance exercise movements.The maximum deviation of estimated values was relatively high,and the estimation formulas could provide a reference in practical application,instead of replacing the actual measuremented values.In the future,it is necessary to increase the sample size to improve the accuracy of the estimation formulas. |
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