Steadiness is reduced and motor unit discharge is more variable in old adults

Laidlaw, Douglass H.; Beznoska, Martin; Enoka, Roger M.

doi:10.1002/(sici)1097-4598(200004)23:4<600::aid-mus20>3.3.co;2-4

Cited by 109 publications

(219 citation statements)

References 8 publications

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“…The physiological mechanism of the age-related reduction in steadiness (greater force variability) is not fully understood, but is thought to be related to a complex mixture of changes in motor unit discharge rate variability and synchronization (Knight and Kamen 2004;Kornatz et al 2004Kornatz et al , 2005Laidlaw et al 2000;Semmler et al 2003;Yao et al 2000). Resistance training can increase the ability to control force fluctuations during muscle contractions in healthy older adults (Hortobagyi et al 2001;Keen et al 1994;Kornatz et al 2005;Laidlaw et al 1999;Tracy et al 2004).…”

Section: Introductionmentioning

confidence: 72%

“…This also contradicts several studies in the hand muscles, which suggest that lengthening contractions produce greater fluctuations than shortening contractions (Christou et al 2003a, b;Kornatz et al 2005;Laidlaw et al 2000). Because lengthening contractions have a greater maximal force capacity, the difference between contraction types at Groups that showed statistical significance or trends for significance are noted next to symbol.…”

Section: Steadiness Adaptationsmentioning

confidence: 99%

“…However, the magnitude of the training effect seems to be dependent on the muscle group , contraction type (Tracy et al 2004), the initial level of steadiness Tracy et al 2004), but not on the intensity of training (Hortobagyi et al 2001;Kornatz et al 2005;Laidlaw et al 1999). For example, following resistance training in the first dorsal interosseus muscle, older adults were more steady during submaximal isometric Keen et al 1994;Laidlaw et al 1999) and shortening and lengthening contractions (Kornatz et al 2005;Laidlaw et al 2000). However, results differ following knee extensor training where older adults were more steady only during shortening and lengthening (Hortobagyi et al 2001;Tracy et al 2004), but not during isometric contractions (Bellew 2002).…”

Section: Introductionmentioning

confidence: 99%

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Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

et al. 2005

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The purpose of this study was to determine the effect of task-specificity on knee extensor steadiness adaptations in functionally limited older adults. Twenty-four functionally limited older adults (74.6+/-7.6 years: 22 women, 2 men) completed a 10-week control period followed by 10 weeks (2 days/week) of resistance (RT), functional (FT) (practicing everyday tasks, i.e., chair rises) or functional + resistance (FRT) training, which featured both shortening and lengthening movements. During testing, subjects performed a steady isometric [10, 25, 50% of maximal voluntary contraction (MVC)] and shortening/lengthening (5, 30, 65% of MVC) knee extensor contractions. There were no steadiness (isometric, shortening or lengthening contractions) changes in the control period and no adaptations in isometric steadiness due to training. RT induced a 37% reduction in shortening fluctuations at 5% of MVC and 35% reduction in lengthening fluctuations at both 30% and 65% of MVC. FRT induced a 60% reduction in shortening fluctuations at 30% of MVC. No adaptations in dynamic steadiness were observed in the FT group. Further analysis indicated that those who were the least steady at baseline showed the greatest training effects during isometric (RT: R (2)=0.25, FRT: R (2)=0.49, FT: R (2)=0.38), shortening (RT: R (2)=0.36, FRT: R (2)=0.36, FT: R (2)=0.35) and lengthening (RT: r (2)=0.29, FRT: r (2)=0.44) contractions. In conclusion, steadiness improvements in groups performing resistance exercise, without a concomitant improvement in the FT group, supports a role for task-specificity in explaining steadiness adaptations, particularly for unsteady older adults.

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Section: Introductionmentioning

confidence: 72%

Section: Steadiness Adaptationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

et al. 2005

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“…However, we did observe that women had greater force fluctuations at task failure, which could be indicative of an increased level of excitatory drive (Lo¨scher et al 1996). However, because there was no association between force fluctuations at task failure and time to task failure it seems probable the greater force fluctuations were due to another factor, as a number of mechanisms are thought to contribute to fluctuation in muscle force output such as increased motor unit synchronization or alterations in muscle activation (Laidlaw et al 2000;Semmler 2002;Shinohara et al 2003).…”

Section: Sex Differences In Fatigue Are Blood Flow Dependentmentioning

confidence: 99%

Sex differences in muscle fatigability and activation patterns of the human quadriceps femoris

et al. 2005

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The purposes of this study were to determine if the fatigability of the quadriceps femoris varies by biological sex under conditions of normal muscle blood flow and ischemia, and if differences in neuromuscular activation patterns exist. Young men and women (n = 11/group; age 20-39 years) performed a sustained knee extension contraction at 25% of maximal force under conditions of occluded (OCC) and normal muscle blood flow (NON-OCC). Electromyographic (EMG) activity was recorded from the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM) and biceps femoris (BF) muscles, and analyzed for fatigue-induced changes in the amplitude and burst rate and duration (transient changes in motor unit recruitment) of the signal. Additionally, force fluctuations during the sustained contraction were quantified. Women had a longer time to task failure during the NON-OCC task [214.9 +/- 20.5 vs. 169.1 +/- 20.5 (SE) s] (P = 0.02), but not during the OCC task (179.6 + 19.6 vs. 165.2 +/- 19.6 s). EMG data demonstrated sex differences in the neuromuscular activation pattern of the RF muscle and the collectively averaged QF muscles. During the NON-OCC and OCC tasks women achieved a higher relative activation of the RF at task failure than men (NON-OCC: 40.68 +/- 4.57 vs. 24.49 +/- 4.19%; OCC: 36.80 +/- 5.45 vs. 24.41 +/- 2.12%) (P = 0.02 and 0.05, respectively). Also, during both tasks, they demonstrated a greater relative activation at task failure than men when an average of the VL, VM and RF was considered. Additionally, women exhibited a greater coefficient of variation in force fluctuations during the last-third of the fatiguing NON-OCC task (6.21 +/- 0.567 vs. 4.56 +/- 0.56%) (P = 0.001). No sex differences in EMG burst rate or duration were observed, although there was a trend towards greater EMG burst rate of the RF in association with muscle fatigue in the women (P = 0.09). Interestingly, the only neuromuscular activation variable that displayed a significant relationship with the time to task failure was the average relative EMG of the QF at task failure, and this relationship was observed under both experimental blood flow conditions (NON-OCC: r = 0.47, P = 0.03; OCC: r = 0.44, P = 0.04). These results indicate that sex differences in muscle blood flow and/or muscle metabolism are in part responsible for the female advantage in fatigue-resistance. Additionally, these findings suggest that men synergistically recruit the RF compartment to a lesser extent than women in association with muscle fatigue, and that women achieve an overall greater relative activation of the QF at task failure than men. However, the implications of these sex differences in neuromuscular activation patterns during fatiguing muscular contractions on the ability to withstand muscle fatigue (prolonged time to task failure) does not appear to be causally related.

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“…3). These greater force fluctuations are associated with a greater variability of the MU discharge rate (Laidlaw et al 2000). It seems thus that the MMG signal reflects more variations in the recruitment process and force impairment due to localised muscle fatigue during intermittent contraction than during continuous contraction, where others factors like physiological tremor and changes in the muscle physical milieu are also important.…”

Section: Rating Of Perceived Exertion)mentioning

confidence: 99%

Development of muscle fatigue as assessed by electromyography and mechanomyography during continuous and intermittent low-force contractions: effects of the feedback mode

et al. 2002

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The goal of the present study was to investigate the significance of low-force continuous or intermittent static contraction and feedback mode (visual or proprioceptive) on the development of muscle fatigue as assessed by electromyography (EMG) and mechanomyography (MMG). Visual (force control) and proprioceptive (displacement control) feedback was investigated during intermittent (6 s contraction, 4 s rest) and continuous static contractions at 10% and 30% of the maximum voluntary contraction (MVC). Mean force, force fluctuation, rating of perceived exertion and root mean square (RMS) and mean power frequency (MPF) of the EMG and MMG signals were analysed. The general pattern for MMG RMS and EMG RMS values and the rating of perceived exertion was an increase with contraction time, while the EMG MPF values decreased ( P<0.05). The increase in RMS values was generally more pronounced for the MMG compared with the EMG, while the decrease in MPF values was more consistent for the EMG compared with the MMG signal. During the intermittent contractions, the main effect was on MPF for both EMG and MMG. Lower force fluctuation and larger rating of perceived exertion ( P<0.05), greater slopes of EMG and MMG RMS and MPF values versus time were observed with proprioceptive feedback compared with visual feedback. The findings suggest that (1) the EMG and MMG signals give complementary information about localised muscle fatigue at low-level contraction: they responded differently in terms of changes in the time and frequency domain during continuous contraction, while they responded in concert in the frequency domain during intermittent contractions, and (2) the different centrally mediated motor control strategies used during fatiguing contraction may be dependent upon the feedback modality.

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Steadiness is reduced and motor unit discharge is more variable in old adults

Cited by 109 publications

References 8 publications

Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

Sex differences in muscle fatigability and activation patterns of the human quadriceps femoris

Development of muscle fatigue as assessed by electromyography and mechanomyography during continuous and intermittent low-force contractions: effects of the feedback mode

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