Relationships between nitric oxide biomarkers and physiological outcomes following dietary nitrate supplementation

Dietary nitrate (NO3-) supplementation can increase nitric oxide (NO) bioavailability, reduce blood pressure (BP) and improve muscle contractile function in humans. Plasma nitrite concentration (plasma [NO2-]) is the most oft-used biomarker of NO bioavailability. However, it is unclear which of several NO biomarkers (NO3-, NO2-, S-nitrosothiols (RSNOs)) in plasma, whole blood (WB), red blood cells (RBC) and skeletal muscle correlate with the physiological effects of acute and chronic dietary NO3- supplementation. Using a randomized, double-blind, crossover design, 12 participants (9 males) consumed NO3--rich beetroot juice (BR) (∼12.8 mmol NO3-) and NO3--depleted placebo beetroot juice (PL) acutely and then chronically (for two weeks). Biological samples were collected, resting BP was assessed, and 10 maximal voluntary isometric contractions of the knee extensors were performed at 2.5-3.5 hours following supplement ingestion on day 1 and day 14. Diastolic BP was significantly lower in BR (-2 ± 3 mmHg, P=0.03) compared to PL following acute supplementation, while the absolute rate of torque development (RTD) was significantly greater in BR at 0-30 ms (39 ± 57 N.m.s-1, P=0.03) and 0-50 ms (79 ± 99 N.m.s-1, P=0.02) compared to PL following two weeks supplementation. Greater WB [RSNOs] rather than plasma [NO2-] was correlated with lower diastolic BP (r=-0.68, P=0.02) in BR compared to PL following acute supplementation, while greater skeletal muscle [NO3-] was correlated with greater RTD at 0-30 ms (r=0.64, P=0.03) in BR compared to PL following chronic supplementation. We conclude that [RSNOs] in blood, and [NO3-] in skeletal muscle, are relevant biomarkers of NO bioavailability which are related to the reduction of BP and the enhanced muscle contractile function following dietary NO3- ingestion in humans.

Exercise-induced fatigue affects knee proprioceptive acuity and quadriceps neuromuscular function more in patients with ACL reconstruction or meniscus surgery than in healthy individuals

PURPOSE

To observe how knee proprioceptive acuity and quadriceps neuromuscular function change during and after repeated isokinetic knee-extension exercise in patients with anterior cruciate ligament reconstruction (ACLR) or meniscus surgery.

METHODS

Patients with ACLR or meniscus surgery and matched controls (n = 19 in each group) performed knee-flexion replication at 15° and 75°, and quadriceps peak torque (PT), central activation ratio (CAR) and rate of torque development (RTD) at baseline and immediately after every five sets of isokinetic knee-extension exercise (times 1-5).

RESULTS

Compared to the baseline, the ACLR and control groups displayed errors in knee-flexion replication at 75° only at time 5 (115.9-155.6%; p ≤ 0.04, d ≥ 0.97), whereas the meniscus surgery group exhibited errors at all time points (142.5-265.6%; p ≤ 0.0003, d ≥ 1.4). Significant percentage reductions in quadriceps CAR were observed between times 4 and 5 in the ACLR group (-5.8%; p = 0.0002, d = 0.96), but not in the meniscus surgery (-1.4%; n.s.) and control (0.1%; n.s.) groups. Significant percentage reductions in quadriceps RTD were observed between times 4 and 5 in the ACLR (-24.2%; p = 0.007, d = 0.99) and meniscus surgery (-23.0%; p = 0.01, d = 0.85) groups, but not in the control group (-0.2%; n.s.).

CONCLUSION

Patients with ACLR or meniscus surgery displayed a greater loss in knee proprioceptive acuity and quadriceps neuromuscular function during and after exercise than healthy individuals. Evidence-based interventions to enhance exercise-induced fatigue resistance should be implemented following ACLR or meniscus surgery, aiming to prevent proprioceptive and neuromuscular changes within the knee joint and quadriceps.

LEVEL OF EVIDENCE

III.

Explosive hamstrings strength asymmetry persists despite maximal hamstring strength recovery following anterior cruciate ligament reconstruction using hamstring tendon autografts

PURPOSE

To investigate the differences in maximal (isometric and concentric peak torque) and explosive (rate of torque development (RTD)) hamstring and quadriceps strength symmetry between males and females during early- and late-phase rehabilitation after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts and to determine the interaction of time and sex on maximal and explosive strength symmetry.

METHODS

A total of 38 female and 51 male participants were assessed during early (3-6 months post-operative) and late (7-12 months post-operative) phases of rehabilitation following ACLR. Maximal (concentric and isometric peak torque) and explosive (isometric RTD) hamstring and quadriceps strength were assessed and presented as limb symmetry index (LSI).

RESULTS

Maximal concentric hamstrings asymmetry (Early: 86 ± 14; Late 92 ± 13; p = 0.005) as well as maximal concentric (Early, 73 ± 15; Late 91 ± 12; p < 0.001) and explosive (Early: 82 ± 30; Late: 92 ± 25; p = 0.03) quadriceps asymmetry decreased from early to late rehabilitation. However, there were no significant changes in maximal isometric quadriceps strength and explosive isometric hamstring strength in the same time period. Females had a larger asymmetry in maximal concentric (Females: 75 ± 17; Males: 81 ± 15; p = 0.001) and explosive (Females: 81 ± 32; Males: 89 ± 25; p = 0.01) quadriceps strength than males throughout rehabilitation. There were no sex differences in maximal and explosive hamstring strength. There were no sex by time interactions for any variables.

CONCLUSION

Explosive hamstring strength asymmetry did not improve despite recovery of maximal hamstring strength during rehabilitation following ACLR with HT autografts. While sex did not influence strength recovery, females had larger maximal and explosive quadriceps strength asymmetry compared to males throughout rehabilitation following ACLR.

LEVEL OF EVIDENCE

Level III.

Association of age-related decrease in intracellular-to-total water ratio with that in explosive strength of the plantar flexors: a cross-sectional study

Background

We aimed to investigate the association of age-related differences in the intracellular-to-total water ratio with explosive strength of the plantar flexors.

Methods

A total of 60 young (21–33 years) and older (64–83 years) individuals were recruited. Intracellular- (ICW) and total-water (TW) content within the right leg was evaluated by bioelectrical impedance spectroscopy as indicators of muscle cell mass and whole muscle mass within the segment, respectively. ICW divided by TW (ICW/TW) was calculated as an index of the occupancy of muscle cells within whole muscle. Rate of torque development (RTD) and electromyography (EMG) activity during maximal voluntary isometric plantar flexion were measured as indicators of explosive muscle strength and neuromuscular activity, respectively. RTD was calculated from three time windows of 0–50, 50–100, and 100–200 ms. Time-to-peak torque (TPT) was assessed from evoked twitch contraction.

Results

Compared with young participants, older participants showed lower ICW/TW (−7%, P < 0.001), RTD (−25 to −40%, P = 0.003 to 0.001), and longer TPT (+11%, P < 0.001). ICW/TW associated positively with RTD (r = 0.377 to 0.408, P = 0.004 to 0.001) and negatively with TPT (r = −0.392, P = 0.002), but not with EMG activity. RTD was associated positively with EMG for each time window (r = 0.527 to 0.607, P < 0.001).

Conclusions

These results indicate that ICW/TW may be a useful predictor of the age-related decrease in RTD, and that the decrease in ICW/TW with age may reflect age-associated changes in intrinsic contractile properties.

Passive and active muscle elasticity of medial gastrocnemius is related to performance in sprinters

PURPOSE

Limited information is available on the association between muscle material properties and sprint performance. We aimed to identify whether and how the elasticity of passive and active muscle of the medial gastrocnemius (MG) is related to sprint performance.

METHODS

MG shear wave speed was measured under passive and active (20%, 50%, 80% of maximal voluntary contraction [MVC]) conditions, with ultrasound shear wave elastography, in 18 male sprinters. Passive and active ankle joint stiffness was assessed by applying a short-range fast stretch during 0%, 20%, 50%, and 80% MVC of plantar flexion. Additionally, rate of torque development (RTD) during explosive plantar flexion was measured.

RESULTS

Passive and active MG shear wave speed was negatively correlated with 100-m race time. Passive MG shear wave speed was positively correlated with RTD, and RTD was negatively correlated with 100-m race time. MG shear wave speed at 50% and 80% MVC showed a positive correlation with ankle joint stiffness at the corresponding contraction level, and ankle joint stiffness at 50% and 80% MVC showed negative correlations with 100-m race time. These correlations were significant even after controlling for MVC torque.

CONCLUSION

Our findings indicate that passive and active muscle elasticity of plantar flexor is important to achieve superior sprint performance. Specifically, high elasticity of passive MG could be related to superior sprint performance through high explosive torque production. In contrast, high elasticity of active MG at moderate-to-high intensity is likely related to high sprint performance through high ankle joint stiffness.

The associations between asymmetries in quadriceps strength and gait in individuals with unilateral transtibial amputation

BACKGROUND

Individuals with unilateral transtibial amputations (ITTAs) are asymmetrical in quadriceps strength. It is unknown if this is associated with gait performance characteristics such as walking speed and limb symmetry.

RESEARCH QUESTION

Are quadriceps strength asymmetries related to walking speed and/ or gait asymmetries in ITTAs?

METHODS

Knee-extensor isometric maximum voluntary torque (MVT) and rate of torque development (RTD) were measured in eight ITTAs. Gait data were captured as the ITTAs walked at self-selected habitual and fast speeds. Step length and single support time, peak knee extension moments and their impulse and peak vertical ground reaction force (vGRF) in the braking and propulsive phases of stance were extracted. Bilateral Asymmetry Index (BAI) and, for gait variables only, difference in BAI between walking speeds (ΔBAI) were calculated. Correlation analyses assessed the relationships between MVT and RTD asymmetry and (1) walking speed; (2) gait asymmetries.

RESULTS

Associations between strength and gait BAIs generally became more apparent at faster walking speeds, and when the difference in BAI between fast and habitual walking speed was considered. BAI RTD was strongly negatively correlated with habitual and fast walking speeds (r=∼0.83). Larger BAI RTD was strongly correlated with propulsive vGRF BAI in fast walking, and larger ΔBAIs in vGRF during both the braking and propulsion phases of gait (r = 0.74-0.92). ITTAs who exhibited greater BAI MVT showed greater ΔBAI in single support time (r = 0.83).

SIGNIFICANCE

While MVT and RTD BAI appear to be associated with gait asymmetries in ITTAs, the magnitude of the asymmetry in RTD appears to be a more sensitive marker of walking speed. Based on these results, it's possible that strengthening the knee-extensors of the amputated limb to improve both MVT and RTD symmetry may benefit walking speed, and reduce asymmetrical loading in gait.

Influence of muscle fatigue on contractile twitch characteristics in persons with parkinson's disease and older adults: A pilot study

Introduction

It is widely accepted that pathophysiological changes to the central nervous system of persons with Parkinson's disease (PD) result in negative effects on motor function. However, less information is known regarding the pathology of PD on skeletal muscle. The purpose of this study was to determine the effect of a fatiguing isometric knee extension protocol on muscle mechanics using evoked twitch contractions in persons with PD and in non-impaired older adults (OLD).

Methods

Evoked twitch contractions were examined during a fatiguing protocol in PD (66 ± 9 yr, n = 8) and OLD (65 ± 10 yr, n = 5). Participants performed 5-sec maximal isometric voluntary contractions of the quadriceps femoris with 5-sec rest for 3-min. Every 30-sec during rest intervals, a maximal transcutaneous electrical stimulus was administered to the quadriceps femoris to quantify evoked peak twitch torque (pTT), peak relaxation rate (pRR), and peak rate of torque development (pRTD).

Results

A large effect of voluntary fatigue (%decline) was observed (g = 1.58). There were no significant differences in pTT (p = 0.09; 95% CI:-3.6, 0.28) or pRR (p = 0.11; 95% CI:-31, 3.6). However, the slope decline of pRTD in OLD (-35.4 ± 24.7) was greater than PD (-11.5 ± 11.4; p = 0.03), indicating that skeletal muscle in persons with PD is less fatigable compared to non-impaired older adults.

Conclusion

The rate, not the maximum capacity, of torque generation of the muscle during a fatiguing knee extension protocol was affected by PD. Future studies are warranted to identify the mechanism(s) responsible for the observed differences in skeletal muscle contractile characteristics and potential myofiber distribution variation in PD.

Relationship between resting medial gastrocnemius stiffness and drop jump performance

Although the influence of the series elastic element of the muscle-tendon unit on jump performance has been investigated, the corresponding effect of the parallel elastic element remains unclear. This study examined the relationship between the resting calf muscle stiffness and drop jump performance. Twenty-four healthy men participated in this study. The shear moduli of the medial gastrocnemius and the soleus were measured at rest as an index of muscle stiffness using ultrasound shear wave elastography. The participants performed drop jumps from a 15 cm high box. The Spearman rank correlation coefficient was used to examine the relationships between shear moduli of the muscles and drop jump performance. The medial gastrocnemius shear modulus showed a significant correlation with the drop jump index (jump height/contact time) (r = 0.414, P = 0.044) and jump height (r = 0.411, P = 0.046), but not with contact time (P > 0.05). The soleus shear modulus did not correlate with these jump parameters (P > 0.05). These results suggest that the resting medial gastrocnemius stiffness can be considered as one of the factors that influence drop jump performance. Therefore, increase in resting muscle stiffness should enhance explosive athletic performance in training regimens.

Adapted protocol of rate of force development and relaxation scaling factor for neuromuscular assessment in patients with knee osteoarthritis

BACKGROUND

The linear relationship between muscle torque and rate of torque rise/relaxation during rapid muscle contractions has been recently introduced as a novel measure of muscle quickness, termed rate of torque development/relaxation scaling factor (RTD-SF/RTR-SF). Because the standard assessment protocol includes potentially painful muscle contractions, the first purpose of this study was to validate an adapted RTD-SF/RTR-SF protocol for knee extensor muscles that utilizes lower submaximal intensities and can be used in knee osteoarthritis patients.

METHODS

A cross-sectional study was performed on a group of healthy controls (n = 24) who underwent the standard RTD-SF/RTR-SF protocol (20-80% of maximum) and the knee osteoarthritis group (n = 24) who underwent the adapted protocol (20-60% of maximum). We calculated the RTD-SF, RTR-SF and the linearity (r²) for both relationships, based on both protocols in controls.

RESULTS

The validity of the adapted protocol was acceptable (intraclass correlation coefficient = 0.77-0.93), with low within-participant variation (coefficient of variability <10%) for both outcome measures. Compared with the control group, the knee osteoarthritis group had similar RTD-SF, but lower linearity of RTD-SF (0.90 vs. 0.82). The RTR-SF (8.0/s vs. 6.7/s) and its linearity (0.87 vs. 0.73) were significantly reduced. Comparing the affected and the unaffected leg in the knee osteoarthritis group, the unaffected leg had greater maximal torque (96.2 vs. 84.1 Nm) and higher linearity for RTD-SF (0.86 vs. 0.80) and RTR-SF (0.82 vs. 0.73).

CONCLUSIONS

We confirmed the validity of the adapted RTD/RTR-SF protocol and its sensitivity to impairments associated with knee osteoarthritis.

Brazilian Jiu-Jitsu fighters present greatest rapid and maximal strength imbalances at extreme elbow angles

BACKGROUND

The performance of Brazilian jiu-jitsu (BJJ) fighters is dependent on rapid and maximal elbow strength actions. Appropriate strength balance between elbow flexors (F) and extensors (E) across the full joint range of motion may be required to decrease risk of injuries.

AIM

To compare rapid and maximal elbow F/E strength balance through full range of motion in BJJ fighters.

MATERIALS AND METHODS

Twenty-three male BJJ fighters (27.9 ± 4.6 years, 82.9 ± 10.9 kg, 174.5 ± 6.8 cm, and 15.3 ± 6.8% body fat) with 8.2 ± 6.5 years of practice volunteered to participate. Participants were tested for rate of torque development (RTD) and peak torque (PT) of elbow F and E at six angles (45°, 60°, 75°, 90°, 105°, and 120°; 0° = full extension). Rapid (F RTD/E RTD) and maximal (F PT/E PT) angle-specific torque (AST) ratios were calculated.

RESULTS

Rapid AST ratio at 45° (0.66 ± 0.18) and maximal AST ratio at 45° (0.91 ± 0.16) and 120° (0.88 ± 0.20) were significantly less than all other AST ratios at mid-point angles of elbow range of motion (p < 0.05). Individual data demonstrates that both beginners and advanced BJJ fighters present overall similar rapid and maximal F/E AST imbalances.

CONCLUSION

BJJ fighters present greater rapid and maximal strength imbalances at extreme-compared to mid-point angles of range of motion. Results may benefit coaches to develop strength exercises focusing on these specific angles to potentially reduce the risk of elbow injury and improve performance of BJJ fighters.

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

INTRODUCTION

This study examined the effects of age and knee position (fully extended, K0; 90° flexed, K90) on plantar flexor maximal voluntary contraction (MVC) torque and the rate of torque development (RTD) in both sexes.

METHODS

The following parameters were measured in 32 older (66-81 yr, 17 males and 15 females) and 37 young (20-30 yr, 18 males and 19 females) adults: evoked peak twitch torque, time to peak twitch torque, RTD of the twitch torque, MVC torque, RTD at early (0-50 ms, RTD_0-50) and later (100-200 ms, RTD_100-200) time intervals during explosive contractions, voluntary activation (VA%) during MVC, root mean square of the electromyogram (RMS-EMG) during MVC and explosive contractions, thickness of the triceps surae, and pennation angle of the medial gastrocnemius. The magnitudes of the differences were interpreted based on Cohen's d (d).

RESULTS

Age-related difference in RTD_0-50 was greater for females (d = 1.36) than males (d = 1.03) and vice versa for MVC torque and RTD_100-200. For young adults, MVC torque, RTDs, and RMS-EMGs of the gastrocnemius but not the soleus were significantly higher in K0 than in K90. For older adults, no differences in voluntary RTDs were observed between K0 and K90, and RMS-EMGs of the gastrocnemius were higher in K90 than in K0, except for that of the lateral gastrocnemius in the early time intervals during explosive contraction. The age-related difference in the effect of knee position for RTD_0-50 was higher in females than males, and vice versa for MVC torque and RTD_100-200.

CONCLUSION

The results suggested that the effects of age and knee joint angle on the plantar flexor performance were more prominent in the early phase of force production for females and were more apparent in the later phase and maximal force for males.

Attenuated activation of knee extensor muscles during fast contractions in older men and women

AIM

Reduced physical function and increased risk of falls in older adults are accompanied by age-related reductions in torque development of leg muscles, although the mechanisms and potential sex differences are not understood.

PURPOSE

To determine the mechanistic origins (neural vs. muscular) for the age-related reduction in torque development, we compared the peak rates of torque development (RTD) during electrically-evoked and fast voluntary contractions of the knee extensors between young and older men and women.

METHODS

Sets of single- and double-pulse electrical stimulations evoked contractions of the knee extensor muscles in 20 young (23.0 ± 0.8 years; 10 women) and 20 older adults (78.2 ± 1.5 years; 10 women), followed by voluntary isometric knee extension contractions with torque development as fast as possible that matched the torque during electrically-evoked contraction (10-40% maximal torque).

RESULTS

Peak RTD during fast-voluntary contractions was 41% less than electrically-evoked contractions (p < 0.001), but more so for older adults (44%) than young (38%, p = 0.04), with no sex differences. Peak RTD during fast-voluntary contractions was more variable between contractions for the older than young adults (77%MVC s^-1 vs. 47%MVC s^-1, p < 0.001). Additionally, older women exhibited greater variability than older men (81%MVC s^-1 vs. 72%MVC s^-1, p = 0.04) with no sex-related differences within the young adults.

CONCLUSION

Older adults had slower and more variable RTD during voluntary contractions than young adults, particularly older women. The limited age-related differences in electrically-evoked RTD suggest the primary mechanism for the slower torque development of the knee extensor muscles in older men and women involve reduced neural activation.

Factors influencing bilateral deficit and inter-limb asymmetry of maximal and explosive strength: motor task, outcome measure and muscle group

PURPOSE

The purpose of the present study was to investigate the influence of strength outcome [maximal voluntary contraction (MVC) torque vs. rate of torque development (RTD)], motor task (unilateral vs. bilateral) and muscle group (knee extensors vs. flexors) on the magnitude of bilateral deficits and inter-limb asymmetries in a large heterogeneous group of athletes.

METHODS

259 professional/semi-professional athletes from different sports (86 women aged 21 ± 6 years and 173 men aged 20 ± 5 years) performed unilateral and bilateral "fast and hard" isometric maximal voluntary contractions of the knee extensors and flexors on a double-sensor dynamometer. Inter-limb asymmetries and bilateral deficits were compared across strength outcomes (MVC torque and multiple RTD measures), motor tasks and muscle groups.

RESULTS

Most RTD outcomes showed greater bilateral deficits than MVC torque for knee extensors, but not for knee flexors. Most RTD outcomes, not MVC torque, showed higher bilateral deficits for knee extensors compared to knee flexors. For both muscle groups, all RTD measures resulted in higher inter-limb asymmetries than MVC torque, and most RTD measures resulted in greater inter-limb asymmetries during unilateral compared to bilateral motor tasks.

CONCLUSIONS

The results of the present study highlight the importance of outcome measure, motor task and muscle group when assessing bilateral deficits and inter-limb asymmetries of maximal and explosive strength. Compared to MVC torque and bilateral tasks, RTD measures and unilateral tasks could be considered more sensitive for the assessment of bilateral deficits and inter-limb asymmetries in healthy professional/semi-professional athletes.

Rapid hamstrings to quadriceps ratio at long muscle lengths in professional football players with previous hamstring strain injury

Hamstring strain injuries (HSI) are the most common injury in male professional football and are potentially a primary risk factor to re-injury. Although the isokinetic strength ratios have often been used to identify strength imbalances that can augment the risk of injury in football players, the rate of torque development hamstring to quadriceps ratio (RTD H/Q) has rarely been considered in previous reports. Furthermore, little consideration has been given to selective hamstring lengths (30° of knee flexion) and its influence on torque production. The aim of this study was to investigate the RTD H/Q at long hamstring lengths, conventional (concentric/concentric) and functional (eccentric/concentric) H/Q ratios in football players with and without previous HSI. Twenty-four professional male football players (12 and 12 without previous HSI) performed maximal voluntary isometric contractions at long hamstring lengths (knee and hip flexed at 30° and 85°, respectively) and isokinetic concentric and eccentric contractions at 180°.s^-1 and 60°.s^-1. Conventional and functional H/Q ratios based on peak torque throughout the entire isokinetic range of motion and at long hamstring lengths were calculated. The RTD H/Q was extracted at long hamstring lengths in incrementing time periods of 50 milliseconds (ms) from the onset of contraction (50-250 ms). No significant differences were found between groups in any H/Q ratios studied. However, small effects (d = 0.4) were found in previously injured hamstrings to lower RTD H/Q at 50 ms and flexor eccentric torque. Previous HSI group showed small to moderate (0.4 > d < 0.6) higher RTD H/Q in late time intervals (>100 ms).

Corticomotor function is associated with quadriceps rate of torque development in individuals with ACL surgery

Impaired corticomotor function arising from altered intracortical and corticospinal pathways are theorized to impede muscle recovery following anterior cruciate ligament (ACL) surgery, yet functional implications of centrally driven adaptations remain unclear. We aimed to assess relationships between quadriceps corticomotor and neuromechanical function after ACL surgery, and to compare with contralateral and control limbs. 16 individuals after primary, unilateral ACL surgery and 16 sex- and age-matched controls participated. Corticomotor function was assessed using transcranial magnetic stimulation, and quantified via active motor thresholds (AMT), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Neuromechanical function was quantified via electromechanical delay, early and late-phase rate of torque development (RTD_0-50, RTD_100-200), coefficient of variation, maximal voluntary isometric contraction (MVIC) torque, and central activation ratio. We observed significant correlations in the ACL limbs between: AMT and RTD_0-50 (r = - 0.513, p = 0.031), SICI and RTD_100-200 (r = 0.501, p = 0.048), AMT and SICI (r = - 0.659, p = 0.010), AMT and ICF (r = 0.579, p = 0.031), RTD_0-50 and MVIC (r = 0.504, p = 0.023), and RTD_100-200 and MVIC (r = 0.680, p = 0.002). The ACL limbs demonstrated higher AMT compared to controls (44.9 ± 8.4 vs. 30.1 ± 8.2%, p < 0.001), and lesser MVIC torque (2.37 ± 0.52 vs. 2.80 ± 0.59 Nm/kg, p = 0.005) and RTD_100-200 (6.79 ± 1.72 vs. 7.90 ± 1.98 Nm/kg/s, p = 0.006) compared to the contralateral limbs. Our findings indicate that lesser corticospinal excitability is associated with lesser early-phase RTD, and greater intracortical inhibition is associated with lesser late-phase RTD. These findings provide evidence of implications of altered intracortical and corticospinal pathways relative to the ability to rapidly generate quadriceps torque following ACL surgery.

Associations between isometric quadriceps strength characteristics, knee flexion angles, and knee extension moments during single leg step down and landing tasks after anterior cruciate ligament reconstruction

BACKGROUND

It is unclear of how peak knee extension torque and early rate of torque development outcomes are related to lower extremity loading and sagittal plane movement in activities of daily living and landing tasks despite consistent deficits after anterior cruciate ligament reconstruction. The purpose of this cross-section study is to assess the ability of quadriceps strength characteristics to predict movement patterns during a step down and single leg drop crossover hopping tasks.

METHODS

Fifty-two individuals with a unilateral history of anterior cruciate ligament reconstruction completed three trials of the step down and crossover hopping tasks on their involved limb. Participants completed three isometric knee extension contractions at 90° knee flexion with visual feedback to assess peak knee extension torque and rate of torque development during the first 0-100 ms and 100-200 ms of the contraction.

FINDINGS

Peak knee extension torque explained the greatest variance in peak knee extension moment (R² = 40.4%, p < 0.001) and knee flexion angle (R² = 46.7%, p < 0.001) during the crossover hop landing. Rate of torque development (0-100 ms) was the only predictor of knee flexion angle (R² = 19.8%, p = 0.01) at initial contact during the crossover hopping landing. Rate of torque development (100-200 ms) explained 17.6% of the variance in peak knee extension moment during the step down (p = .03).

INTERPRETATION

Peak knee extension torque and early rate of torque development outcomes demonstrate limited relationships between movement of activities of daily living and sport-specific tasks. These limitations should be considered when interpreting the results of isometric strength testing in a clinical setting.

Neuromuscular function of the plantar flexors and predictors of peak power in middle-aged and older males

Little evidence exists regarding the contribution of torque and velocity to the age-related decrease in peak power (PP) for the plantar flexors (PFs). A comprehensive assessment of PF neuromuscular function is necessary to elucidate age-related changes, especially between middle-aged and older adults, in order to identify early, age-related decrements. Thus, the purpose of this study was to examine neuromuscular function of the PFs in middle-aged and older males, and identify predictors of PP. Twenty-eight healthy, middle-aged (n = 13; 45.1 ± 2.7 yrs) and older (n = 15; 65.3 ± 3.2 yrs) males performed concentric isotonic PF contractions ranging in intensity from 20% to 70% isometric strength using a dynamometer. PP in addition to velocity and torque at the moment in time PP occurred, as well as the rate of velocity, torque (RTD), and power (RPD) development were recorded. The rate of electromyography rise (RER) was derived from the linear slope of the normalized electromyography signal. Isometric and concentric dynamic strength were assessed, as well as cross-sectional area and muscle quality (i.e., echo intensity) of the PFs via panoramic ultrasonography. The relationship between serum c-terminal agrin levels and select variables was examined to explore the potential role of neuromuscular junction deterioration. Appendicular lean mass and physical activity level were similar between groups (p > 0.05), and only PP (p = 0.046; d = 0.79), RPD (p = 0.026; d = 0.90), RTD (p = 0.022; d = 0.91), and RER (p = 0.010; d = 1.04) were lower in older males. When groups were collapsed, RTD was the only significant predictor of PP, while c-terminal agrin levels were not associated with any variables. Our findings indicate that PP and time-dependent parameters of muscle activation and contractile function of the PFs are dramatically diminished in older adults compared to middle-aged adults. PP is produced at the same velocity and relative intensity in middle-aged and older males, and RTD is most influential for PP. The inability of the PFs to be rapidly activated appeared to be influential for the age-related impairment in PP and time-dependent contractile parameters.

Rate of torque development and the risk of falls among community dwelling older adults in Japan

BACKGROUND

Rate of torque development (RTD) is defined as the slope of the torque-time curve obtained during an isometric contraction. Several studies have shown that RTD is lower in fallers than in nonfallers. However, these studies had small sample size and was not adjusted confounding factors.

RESEARCH QUESTION

Is RTD associated with falls history in healthy community dwelling older adults.

METHODS

This was cross-sectional study. In total, 122 participants aged ≥65 (mean, 71.3 ± 4.4) years were recruited for this study. We assessed RTD, muscle strength, functional capacity, and physical activity. We assessed RTD over the first 200 ms of the maximal isometric contraction, whereby the onset of contraction was deemed as the point at which torque had risen 4 Nm above the baseline. Differences between the 3 groups (no fall group, single fall group and multiple falls group) were examined using one-way analysis of variance or Kruskal-Wallis test. A post-hoc Bonferroni or Games-Howell test was used to assess the differences between the individual groups. A multivariate multinomial logistic model was built using the factors associated with the fall category.

RESULTS

RTD was significantly different between the no fall group and multiple falls group (P = 0.047). Similarly, RTD was significantly different between the single fall group and multiple falls group (P = 0.016). RTD was associated with both the no fall group and single fall group (odds ratio = 2.05, 95% confidence interval: 1.06-3.97, odds ratio = 2.45, 95% confidence interval: 1.20-4.98, respectively) in multinomial logistic regression.

SIGNIFICANCE

This is the first study to investigate the relationship between RTD and falls history in community-dwelling older adults in multivariate analysis. RTD is more strongly associated with falls history than other performance measures in community-dwelling elderly.

Contribution of hip abductor-adductor muscles on static and dynamic balance of community-dwelling older adults

BACKGROUND

The previous studies have investigated causes of and risk factors for falls and impairment of functional capability in older adults. However, the biomechanical factors involved in functional performance and postural control, and the contribution of hip muscles, are still unknown.

AIMS

The aim of the present study was to verify the association between the muscle function of hip abductors and adductors and static and dynamic balance, in a narrow base of support, in community-dwelling older adults.

METHODS

Eighty-one older adults, including both women and men, were evaluated. Tandem gait and single-leg stance were used to assess static and dynamic balance, and an isokinetic dynamometer was used to analyze muscle function (peak torque and rate of torque development according to body weight). Data were analyzed by a multivariate linear regression test without adjustment and with adjustment using two models: adjustment I (sex) and adjustment II (age).

RESULTS

There was a statistically significant association between peak torque of abductor in single-leg stance and tandem gait speed. The PT of hip adductors contributed to static balance performance, in a narrow base of support from the unadjusted data and from the adjusted data by sex.

CONCLUSION

The findings of the present study are relevant, because if deficits in balance and functionality in older adults can be linked to a decline in maximum muscle strength of hip abductors, this parameter can be treated to maintain independence in older adults for as long as possible.

Rate of torque development is the primary contributor to quadriceps avoidance gait following total knee arthroplasty

BACKGROUND

Following rehabilitation for total knee arthroplasty, "quadriceps avoidance gait", defined by limited knee flexion angle excursion during walking, persists and contributes to poor long-term outcomes. Given the presence of several post-surgical impairments, identifying the contribution of multiple factors to knee flexion angle excursion is important to developing targeted interventions to improve recovery after total knee arthroplasty.

RESEARCH QUESTIONS

Which outcomes continue to improve following rehabilitation for total knee arthroplasty? What are the primary contributors to impaired knee flexion angle excursion during walking following total knee arthroplasty?

METHODS

Peak muscle strength and rate of torque development of the quadriceps, hip abductors, and hip external rotators, five-time sit-to-stand test, Knee Injury & Osteoarthritis Outcome Score, and gait mechanics were assessed in 24 participants at three and six months post-surgery. Paired sample t-tests or Wilcoxon Signed-Rank tests were used to compare outcomes between assessments. Stepwise multiple linear regression were used to assess the contribution of each measure to knee flexion angle excursion.

RESULTS

Significant improvements were noted in all outcomes except hip external rotation rate of torque development, gait speed, and knee flexion angle excursion. Quadriceps rate of torque development and knee pain significantly contributed to knee flexion angle excursion at three months (Adjusted R² = 0.342), while quadriceps rate of torque development and peak hip external rotation strength significantly contributed at six months (Adjusted R² = 0.436).

SIGNIFICANCE

While higher pain levels at three months and greater peak hip external rotation muscle strength at six months contribute to impaired knee flexion angle excursion, quadriceps rate of torque development was the primary contributor to knee flexion angle excursion at both three and six months after surgery. Implementing strategies to maximize quadriceps rate of torque development during rehabilitation may help to reduce quadriceps avoidance gait after total knee arthroplasty.

Functional capacity improves in-line with neuromuscular performance after 12 weeks of non-linear periodization strength training in the elderly

BACKGROUND

While it is accepted that resistance training can improve functional capacity in older individuals, the neuromuscular source of this improvement has yet to be identified.

AIM

This study investigated the link between improved neuromuscular performance and functional capacity after a 12-week resistance training period in untrained healthy older individuals.

METHODS

Fifteen older men and women (60-71 years) adhered to a 4-week control period, followed by 12 weeks of non-linear resistance training for the lower limbs. Maximum dynamic leg press strength (1-RM), maximum isometric knee extension torque and rate of torque development (RTD) were evaluated at - 4, 0, 4, 8, and 12 weeks, and muscle activity was assessed at 0, 4, 8, and 12 weeks. Functional capacity tests (chair rise, stair ascent and descent, and timed up and go) were performed at - 4, 0, and 12 weeks.

RESULTS

No changes occurred during the control period, but the group increased their 1-RM strength (from 142 ± 53 to 198 ± 43 kg, p = 0.001), which was accompanied by an increase in vastus lateralis activation (p = 0.008) during the intervention. Increase was observed at all RTD time intervals at week 8 (p < 0.05). Significant improvements in all the functional capacity tests were observed at week 12 (p < 0.05).

DISCUSSION

Despite the expected increase in strength, RTD, muscle activity, and functional capacity, there was no significant relationship between the changes in neuromuscular performance and functional capacity. While resistance training elicits various positive improvements in healthy older individuals, actual strength gain did not influence the gain in functional capacity.

CONCLUSION

The present study highlights the exact cause that improved the functional capabilities during resistance training are currently unknown.

Age-related effects on maximal and rapid hamstrings/quadriceps strength capacities and vertical jump power in young and older females

BACKGROUND AND AIMS

Declines in hamstrings and quadriceps maximal and rapid strength are commonly reported as a consequence of aging; however, few studies have investigated the influence of age on maximal and rapid hamstrings to quadriceps (H/Q) strength ratios. This study aimed to examine the effects of age on leg extension and flexion maximal and rapid torque production, H/Q strength ratios, and muscle power in healthy, young and old females.

METHODS

Fifteen young (21 ± 2 years) and 15 old (69 ± 7 years) females performed 3 isometric leg extension and flexion maximal voluntary contractions (MVCs), from which peak torque (PT), early (0-30 ms) and late (0-200 ms) phase rate of torque development (RTD), and PT and RTD H/Q strength ratios were extracted. Lower-body peak power output (P _max) was assessed through a vertical jump test.

RESULTS

P _max, PT, and early (RTD30) and late (RTD200) RTD variables of the leg extensors and flexors were lower (P ≤ 0.048) and PT and RTD200 H/Q strength ratios were higher (P ≤ 0.030) in the old compared to the younger females; however, no difference was observed for RTD30 H/Q (P = 0.300). There were also significant negative relationships in the older (r = -0.616 and -0.522; P = 0.014 and 0.046) but not the younger (r = 0.295 and -0.109; P = 0.286 and 0.698) females between P _max and RTD30 and RTD200 H/Q strength ratios.

CONCLUSION

The higher RTD200 H/Q ratio for the older females may contribute to the muscle power deficits often observed in elderly populations. Practitioners may use these findings to help identify older adults with low muscle power capacities and possibly overall functional decline.

Association between rapid force production by the plantar flexors and balance performance in elderly men and women

Plantar flexion strength and balance ability are considered to be crucial for avoiding falls. However, no clear relationship has been established between these two factors in elderly population. This study aimed to examine the association between plantar flexion strength and balance performance in elderly men and women. Forty-three men and 35 women aged over 65 years performed isometric plantar flexion as fast and hard as possible. From the time-torque curve, the rate of torque development in time intervals of 30, 50, 100, 150, and 200 ms from the onset of contraction was determined and normalized to peak torque. In addition, the center of pressure displacement during single-leg standing was calculated and normalized to height. When the data were collapsed over sexes, the normalized rate of torque development was negatively correlated with the normalized center of pressure displacement, except for the time interval of 200 ms. By sex, regardless of the time interval, there was a negative correlation between the normalized rate of torque development and the normalized center of pressure displacement in the elderly men but not in the elderly women. No correlation was seen between the peak torque and normalized center of pressure displacement in either pooled or separated data. The findings suggest that the capability of rapid force production rather than maximal force production of the plantar flexion is important for balance ability in elderly men, but this capability may not be relevant in elderly women.

Is quadriceps muscle strength a determinant of the physical function of the elderly?

[Purpose] To determine the relationships of the quadriceps rate of torque development and the time to peak torque with the physical function of the elderly. [Subjects and Methods] Twenty-one subjects participated in this study. Quadriceps strength was measured using isometric and isokinetic torque tests. Time to peak torque and rate of torque development were calculated from the torque time curve of the isokinetic and isometric torque tests, respectively. Physical activities were measured using 4 physical activity tests. Pearson correlation coefficients were used to examine the relationships among the variables. [Results] The time to peak torque showed significant correlations with all measures of physical activity tests. Rate of torque development showed significant correlation with the timed stair-climbing test. Isometric and isokinetic torques had no significant correlations with any of the physical activity tests. [Conclusion] Time to maximum torque and the rate of torque development might be more important than peak torque in determining the physical function of the elderly.

Time-dependent neuromuscular parameters in the plantar flexors support greater fatigability of old compared with younger males

Older adults are more fatigable than young during dynamic tasks, especially those that involve moderate to fast unconstrained velocity shortening contractions. Rate of torque development (RTD), rate of velocity development (RVD) and rate of neuromuscular activation are time-dependent neuromuscular parameters which have not been explored in relation to age-related differences in fatigability. The purpose was to determine whether these time-dependent measures affect the greater age-related fatigability in peak power during moderately fast and maximal effort shortening plantar flexions. Neuromuscular properties were recorded from 10 old (~ 78 years) and 10 young (~ 24 years) men during 50 maximal-effort unconstrained velocity shortening plantar flexions against a resistance equivalent to 20% maximal voluntary isometric contraction torque. At task termination, peak power, and angular velocity, and torque at peak power were decreased by 30, 18, and 16%, respectively, for the young (p < 0.05), and 46, 28, 30% for the old (p < 0.05) compared to pre-fatigue values with the old exhibiting greater reductions across all measures (p<0.05). Voluntary RVD and RTD decreased, respectively, by 24 and 26% in the young and by 47 and 40% in the old at task termination, with greater decrements in the old (p < 0.05). Rate of neuromuscular activation of the soleus decreased over time for both age groups (~ 47%; p < 0.05), but for the medial gastrocnemius (MG) only the old experienced significant decrements (46%) by task termination. All parameters were correlated strongly with the fatigue-related reduction in peak power (r = 0.81-0.94, p < 0.05), except for MG and soleus rates of neuromuscular activation (r = 0.25-0.30, p > 0.10). Fatigue-related declines in voluntary RTD and RVD were both moderately correlated with MG rate of neuromuscular activation (r = 0.51-0.52, p < 0.05), but exhibited a trend with soleus (r = 0.39-0.41, p = 0.07-0.09). Thus, time-dependent factors, RVD and RTD, are likely important indicators of intrinsic muscle properties leading to the greater age-related decline in peak power when performing a repetitive dynamic fatigue task, which may be due to greater fatigue-related central impairments for the older men than young.