Plantar flexor strength at different knee positions in older and young males and females

Analysis of the rate of force development reveals high neuromuscular fatigability in elderly patients with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) induces muscle wasting and a reduction in the maximum voluntary force (MVF). Little is known about the neuromuscular fatigability in CKD patients, defined as the reduction of muscle force capacities during exercise. Neuromuscular fatigability is a crucial physical parameter of the daily living. The quantification of explosive force has been shown to be a sensitive means to assess neuromuscular fatigability. Thus, our study used explosive force estimates to assess neuromuscular fatigability in elderly CKD patients.

METHODS

Inclusion criteria for CKD patients were age ≥ 60 years old and glomerular filtration rate (GFR) < 45 mL/min/1.73 m2 not on dialysis, and those for controls were GFR > 60 mL/min/1.73 m2 , age and diabetes matched. The fatigability protocol focused on a handgrip task coupled with surface electromyography (sEMG). Scalars were extracted from the rate of force development (RFD): absolute and normalized time periods (50, 75, 100, 150 and 200 ms, RFD50 , RFD75 , RFD100 , RFD150 and RFD200 , respectively), peak RFD (RFDpeak in absolute; NRFDpeak normalized), time-to-peak RFD (t-RFDpeak ) and the relative force at RFDpeak (MVF-RFDpeak ). A statistical parametric mapping approach was performed on the force, impulse and RFD-time curves. The integrated sEMG with time at 0-30, 0-50, 0-100 and 0-200 ms time intervals relative to onset of sEMG activity was extracted and groups were compared separately for each sex.

RESULTS

The cohort of 159 individuals had a median age of 69 (9IQR ) years and body mass index was 27.6 (6.2IQR ) kg/m2 . Propensity-score-matched groups balanced CKD patients and controls by gender with 66 males and 34 females. In scalar analysis, CKD patients manifested a higher decrement than controls in the early phase of contraction, regarding the NRFDpeak (P = 0.009; η2 p  = 0.034) and RFD75 and RFD100 (for both P < 0.001; η2 p  = 0.068 and 0.064). The one-dimensional analysis confirmed that CKD males manifest higher and delayed neuromuscular fatigability, especially before 100 ms from onset of contraction. sEMG was lower in CKD patients than controls in the 0-100 ms (at rest: P = 0.049, Cohen's d = 0.458) and 0-200 ms (at rest: P = 0.016, Cohen's d = 0.496; during exercise: P = 0.006, Cohen's d = 0.421) time windows. Controls showed greater decrease of sEMG than CKD patients in the 0-30 ms (P = 0.020, Cohen's d = 0.533) and 0-50 ms (P = 0.010, Cohen's d = 0.640) time windows. As opposite to females, males showed almost the same differences between groups.

CONCLUSIONS

Our study is the first to show that CKD patients have higher fatigability than controls, which may be associated with an impaired motor-unit recruitment, highlighting a neural drive disturbance with CKD. Further studies are needed to confirm these findings.

Power attenuation from restricting range of motion is minimized in subjects with fast RTD and following isometric training

Time-dependent measures consisting of rate of torque development (RTD), rate of velocity development (RVD), and rate of neuromuscular activation can be used to evaluate explosive muscular performance, which becomes critical when performing movements throughout limited ranges of motion (ROM). Using a HUMAC NORM dynamometer, seven males (27 ± 7 years) and six females (22 ± 3 years) underwent 8 weeks of maximal isometric dorsiflexion training 3 days/week. One leg was trained at 0° (short-muscle tendon unit (MTU) length) and the other at 40° of plantar flexion (long-MTU length). RTD and rate of neuromuscular activation were evaluated during 'fast' maximal isometric contractions. Power, RVD, and rate of neuromuscular activation were assessed during maximal isotonic contractions in four conditions (small (40° to 30° of plantar flexion) ROM at 10 and 50% MVC; large (40° to 0° of plantar flexion) ROM at 10 and 50% MVC) for both legs, pre- and post-training. Despite no change in rate of neuromuscular activation following training, peak power, RTD, and RVD increased at both MTU lengths (p < 0.05). Strong relationships (R²=0.73) were observed between RTD and peak power in the small ROM, indicating that fast time-dependent measures are critical for optimal performance when ROM is constrained. Meanwhile, strong relationships (R²=0.90) between RVD and power were observed at the 50% load, indicating that RVD is critical when limited by load and ROM is not confined. Maximal isometric dorsiflexion training can be used to improve time-dependent measures (RTD, RVD) to minimize power attenuation when ROM is restricted.

Neural and muscular alterations of the plantar flexors in middle-aged women

INTRODUCTION

Considering the large population of middle-aged adults, it is important to understand the age-related change in lower limb muscles and the possible mechanisms before old age (> 65 years old). The purpose of this study was to investigate age-related neural and muscular alterations of the plantar flexors in young and middle-aged women.

METHODS

Twenty two middle-aged (54.0 ± 5.8 yrs) and 17 young (21.8 ± 1.4 yrs) recreationally active women performed rapid maximal voluntary isometric contractions (MVIC) of the plantar flexors. Absolute and normalized rate of torque development (RTD) and electromyography (EMG) were examined. Electrical stimulation was used to examine voluntary activation and contractile properties of the muscle. Ultrasonography was used to examine medial and lateral gastrocnemius muscle thickness and pennation angle. A 6-minute walk and sit to stand task were also performed by all participants.

RESULTS

The middle-aged women had significantly lower MVIC torque (141 ± 49 vs. 109 ± 30 Nm, P = 0.031), absolute RTD (753.0 ± 313.6 vs. 423.0 ± 156.1 Nm/s, P = 0.001), and normalized peak RTD (554.0 ± 191.0 vs. 388.0 ± 91.9% MVIC/s, P = 0.001). Normalized early RTD_0-50 and late RTD_100-200, voluntary activation, and EMG were similar between groups. Resting twitch data showed that time to peak (124.0 ± 20.4 vs. 143.0 ± 16.7 ms, P = 0.002) and half relaxation time (73.1 ± 15.2 vs. 107.0 ± 28.2 ms, P < 0.001) was significantly faster for the young women. Thickness was greater in the lateral gastrocnemius (1.6 ± 0.2 vs. 1.4 ± 0.2 cm, P = 0.006) for the young women. Pennation angle of both muscles were greater for the young women (15.8 ± 3.9 vs. 13.1 ± 2.7 degrees, P < 0.05). Performance of the 6-minute walk was similar between groups, however, the young women performed more repetitions during the sit to stand task (25.6 ± 6.7 vs. 18.3 ± 4.7 reps, P < 0.001).

CONCLUSION

Compared to young women, middle-age women were shown to have lower MVIC torque, peak RTD, and functional performance. Muscle architecture and contractile properties are affected by aging.

Assessment of ankle plantar flexor neuromuscular properties: A reliability study

This study aimed to determine test-retest reliability of ankle plantar flexor neuromuscular properties in healthy people to improve understanding of additional measurement and analysis procedures that may be used in outcome assessment. Ten healthy participants (age 29.60 ± 5.36 years) volunteered. Isometric torque_max, rate of torque development (RTD), rate of electromyography rise (RER), impulse, electromechanical delay (EMD), torque steadiness, and torque sensing were obtained during two testing sessions 60 min apart. ICC values ranged from 0.81 to 0.99, indicating good to excellent test-retest reliability. Lower bands of the 95% CIs were all above 0.75 apart from the early phase measures (≤50 ms) derived from explosive torque-time and EMG-time curves, which were between 0.32 and 0.73, indicating poor to moderate reliability. Heteroscedasticity was observed for RTD, impulse, and EMD. LOA as a function of the mean (X̅) for these measures ranged from mean_difference ± 0.25X̅ to ± 0.68X̅. EMD showed excellent reliability (ICC = 0.90; 95% CI [0.63, 0.98]). Torque sensing and torque steadiness showed good reliability (0.81 ≤ ICC ≤ 0.89). Thus, ankle plantar flexor neuromuscular properties showed good to excellent test-retest reliability. However, reliability of measures in the early phase of muscle contraction were consistently lower than the late phase.

Age-Related Differences in Hip Flexion Maximal and Rapid Strength and Rectus Femoris Muscle Size and Composition

This study aimed to examine the effects of age on hip flexion maximal and rapid strength and rectus femoris (RF) muscle size and composition in men. Fifteen young (25 [3] y) and 15 older (73 [4] y) men performed isometric hip flexion contractions to examine peak torque and absolute and normalized rate of torque development (RTD) at time intervals of 0 to 100 and 100 to 200 milliseconds. Ultrasonography was used to examine RF muscle cross-sectional area and echo intensity. Peak torque, absolute RTD at 0 to 100 milliseconds, and absolute and normalized RTD at 100 to 200 milliseconds were significantly lower (P = .004-.045) in the old compared with the young men. The older men exhibited lower cross-sectional area (P = .015) and higher echo intensity (P = .007) than the young men. Moreover, there were positive relationships between cross-sectional area and absolute RTD at 0 to 100 milliseconds (r = .400) and absolute RTD at 100 to 200 milliseconds (r = .450) and negative relationships between echo intensity and absolute RTD at 100 to 200 milliseconds (r = -.457) and normalized RTD at 100 to 200 milliseconds (r = -.373). These findings indicate that hip flexion maximal and rapid strength and RF muscle size and composition decrease in old age. The relationships observed between ultrasound-derived RF parameters and measurements of RTD suggest that these age-related declines in muscle size and composition may be relevant to hip flexion rapid torque production.