Abstract
In this study, we aimed to discover (1) the effects of age on dynamic balance measures, including the margin of stability (MOS), whole-body angular momentum (
H
), and misalignment of the ...desired and measured centers of pressure (dCOP and mCOP, respectively) in the anteroposterior (AP) and mediolateral (ML) directions, (2) the relationship between gait parameters and these balance measures, and (3) the relationships between these balance measures. We used the kinetic and kinematic data of 151 participants aged 20–77 years from a publicly available database. Participants were divided into three groups: young, middle-aged, and old. The step width of the old group was higher than that of the young group. Age-related differences in dynamic measures were found in the ML direction and not in the AP direction: MOS, peak-to-peak range of
H
, and dCOP–mCOP in the old group were greater than in the young group. ML MOS positively correlated with the frontal peak-to-peak range of
H.
The ML peak-to-peak range of
H
positively correlated with ML dCOP–mCOP across the adult lifespan. Our findings provide new insights for understanding the effects of age on dynamic balance and the relationships between the metrics. Older adults walked with a larger step width, resulting in a large stability margin in the ML direction, although with increased moment and momentum around the center of mass in the frontal plane.
•Effects of aging on required coefficient of friction (RCOF) were investigated.•Older adults walk with lower anteroposterior RCOF owing to a shorter step length.•Older adults walk with higher ...mediolateral RCOF owing to a wider step width.•Gait observed in older adults may cause slips in a more lateral direction.
Slipping is one of the leading causes of falls among older adults. Older adults are considered to walk with a small anteroposterior (AP) component and a large mediolateral (ML) component of the required coefficient of friction (RCOF) owing to a short step length and a wide step width, respectively. However, limited information is available.
What are the effects of aging on the resultant RCOF (RCOFres) and its ML (RCOFML) and AP (RCOFAP) components during straight walking?
We used the kinetic and kinematic data of 188 participants aged 20–77 years from a publicly available database (National Institute of Advanced Industrial Science and Technology Gait Database 2015). The participants were divided into the following three groups: young group (n = 56; age range, 20–34 years), middle-aged group (n = 50; age range, 35–64 years), and old group (n = 82; age range, 65–77 years).
The RCOFres and RCOFAP were lower in the old group than in the other groups, indicating a lower slip risk in this group. However, the RCOFML was higher and the step width was greater in the old group than in the other groups. The higher RCOFML and lower RCOFAP in the old group might be associated with slips in a more lateral direction.
Our findings suggest that older adults have a high risk of slipping in a more lateral direction. Shoes with high-slip resistance in the lateral direction are recommended to prevent hazardous lateral slips among older adults.
Previous findings indicate that co-contractions of plantarflexors and dorsiflexors during quiet standing increase the ankle mechanical joint stiffness, resulting in increased postural sway. Balance ...impairments in individuals with incomplete spinal cord injury (iSCI) may be due to co-contractions like in other individuals with reduced balance ability. Here we investigated the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). Thirteen able-bodied individuals and 13 individuals with iSCI were asked to perform quiet standing with their eyes open (EO) and eyes closed (EC). Kinetics and electromyograms from the tibialis anterior (TA), soleus and medial gastrocnemius were collected bilaterally. The iSCI-group exhibited more co-contractions than the AB-group (EO: 0.208% vs. 75.163%, p = 0.004; EC: 1.767% vs. 92.373%, p = 0.016). Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group (EO: 1.405 cm/s
vs. 0.867 cm/s
, p = 0.023; EC: 1.831 cm/s
vs. 1.179 cm/s
, p = 0.030), but no differences were found for the AB-group (EO: 0.393 cm/s
vs. 0.499 cm/s
, p = 1.00; EC: 0.686 cm/s
vs. 0.654 cm/s
, p = 1.00). To investigate the mechanism, we performed a computational simulation study using an inverted pendulum model and linear controllers. An increase of mechanical stiffness in the simulated iSCI-group resulted in increased postural sway (EO: 2.520 cm/s
vs. 1.174 cm/s
, p < 0.001; EC: 4.226 cm/s
vs. 1.836 cm/s
, p < 0.001), but not for the simulated AB-group (EO: 0.658 cm/s
vs. 0.658 cm/s
, p = 1.00; EC: 0.943 cm/s
vs. 0.926 cm/s
, p = 0.190). Thus, we demonstrated that co-contractions may be a compensatory strategy for individuals with iSCI to accommodate for decreased motor function, but co-contractions may result in increased ankle mechanical joint stiffness and consequently postural sway.
Abstract To examine the age-related deterioration in postural control, we investigated the association between postural sway during quiet standing and either amplitude of physiological tremor or ...muscle volume of the plantar flexors in 20 young and 20 elderly adults. They maintained a quiet standing position on a force platform for 60 s with their eyes open or closed. During quiet standing, physiological tremors detected using a piezoresistive accelerometer were recorded from the soleus muscle, and the center of pressure (COP) displacement and body acceleration in the antero-posterior direction were calculated using the ground reaction forces as an assessment of postural sway. Muscle volume was predicted from muscle thickness by an ultrasonographic image. The physiological tremor of the soleus muscle during quiet standing was significantly greater in elderly than in young adults, and a positive association between physiological tremor and the amplitude of postural sway was found for young and elderly adults combined. Furthermore, physiological tremor was positively correlated with the high-frequency component of COP sway during quiet standing. A significantly negative relation between the muscle volume of the plantar flexors and postural sway was found in both age groups. These results suggest that physiological tremor reflects high-frequency fluctuations in postural sway during quiet standing in young and elderly adults, and age-related increases in the postural sway amplitude in the antero-posterior direction may be related to a decrease in muscle volume of the plantar flexors for maintaining an upright posture.
Background
Transcutaneous electrical stimulation on the motor points over muscle belly, i.e., motor point stimulation (MPS), is widely used in clinical settings, however it is not fully understood ...how MPS recruits motor nerves. Here we investigated the recruitment pattern of the motor nerve and twitch force during MPS and compared to the recruitment during peripheral nerve stimulation (PNS).
Methods
Ten healthy individuals participated in this study. Using MPS on the soleus muscle and PNS on the tibial nerve, a single pulse stimulation was applied with various stimulation intensities from subthreshold to the maximum intensity. We measured the evoked potentials in the lower leg muscles and twitch force. Between MPS and PNS, we compared the recruitment curves of M‐waves and the dynamics of twitch force such as duration from force onset to peak (time‐to‐peak).
Results
The maximum M‐wave was not different between MPS and PNS in the soleus muscle, while it was much smaller in MPS than in PNS in the other lower leg muscles. This reflected the smaller twitch force of plantarflexion in MPS than PNS. In addition, the slope of the recruitment curve for the soleus M‐wave was smaller in MPS than PNS.
Conclusion
Therefore, unlike PNS, MPS can efficiently and selectively recruit motor nerves of the target muscle and gradually increase the recruitment of the motor nerve.
To investigate neuromuscular recruitment pattern in motor point stimulation (MPS), we compared EMGs from lower limb muscles and twitch force between MPS and peripheral nerve stimulation (PNS) on soleus muscle. We found no difference in maximum M‐wave of soleus, smaller M‐wave in adjacent muscles to soleus, and smaller slope of M‐wave recruitment curve in MPS. Thus, MPS efficiently and selectively recruit motor nerves of the target muscle and gradually increase in recruitment of the motor nerve.
Objective: A critical limitation in clinical applications using functional electrical stimulation (FES) for rehabilitation exercises is the rapid onset of muscle fatigue. Spatially distributed ...sequential stimulation (SDSS) has been demonstrated to reduce muscle fatigue during FES compared to conventional single electrode stimulation (SES) in single joint movements. Here we investigated the fatigue reducing ability of SDSS in a clinical application, i.e., FES-rowing, in able-bodied (AB) participants. Methods: FES was delivered to the quadriceps and hamstring of 15 AB participants (five female, ten male) for fatiguing FES-rowing trials using SES and SDSS, participants rowed with voluntary arm effort while endeavoring to keep their legs relaxed. Fatigue was characterized by the time elapsed until a percent decrease occurred in power output (TTF), as well as the trial length indicating the time elapsed until the complete stop of rowing. Result: Trial length was significantly longer in SDSS rowing than in SES (t-test, <inline-formula> <tex-math notation="LaTeX">{p} < 0.01 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{d}=0.71 </tex-math></inline-formula>), with an average SDSS:SES trial length ratio of 1.31 ± 0.47. TTF<inline-formula> <tex-math notation="LaTeX">_{SDSS} </tex-math></inline-formula> was significantly longer than TTF<inline-formula> <tex-math notation="LaTeX">_{SES} </tex-math></inline-formula> with a median TTF<inline-formula> <tex-math notation="LaTeX">_{SDSS} </tex-math></inline-formula>:TTF<inline-formula> <tex-math notation="LaTeX">_{SES} </tex-math></inline-formula> ratio of 1.34 ranging from 1.03 to 5.41 (Wilcoxon Ranked Sum, <inline-formula> <tex-math notation="LaTeX">{p} < 0.01 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{r}=0.62 </tex-math></inline-formula>). No rower experienced a decrease in TTF with SDSS. Conclusion: SDSS reduced fatigue during FES-rowing when compared to SES in AB individuals, resulting in a lengthened FES-rowing period by approximately 30%. Application of SDSS would increase the effectiveness of FES-rowing as rehabilitative exercise for individuals with paralyses.
The F‐wave is a motor response induced by electrical stimulation of peripheral nerves via the antidromic firing of motor nerves, which reflects the motoneuron excitability. To induce F‐waves, ...transcutaneous peripheral nerve stimulation (PNS) is used, which activates nerve branches via transcutaneous electrodes over the nerve branches. An alternative method to activate peripheral nerves, that is, motor point stimulation (MPS), which delivers electrical stimulation over the muscle belly, has not been used to induce F‐waves. In our previous studies, we observed that MPS induced F‐wave‐like responses, that is, motor responses at the latency of F‐waves at a supramaximal stimulation. Here, we further investigated the F‐wave‐like responses induced by MPS in comparison with PNS in the soleus muscle. Thirteen individuals participated in this study. We applied MPS and PNS on the participant's left soleus muscle. Using a monopolar double‐pulse stimulation, the amplitude of the second H‐reflex induced by PNS decreased, whereas the amplitude of the motor response at the F‐wave latency induced by MPS did not decrease. These results suggest that the motor response at the F‐wave latency induced by MPS was not an H‐reflex but an F‐wave. We also found that the F‐wave induced by MPS had a greater amplitude and higher persistence and caused less pain when compared with the F‐waves induced using PNS. We conclude that MPS evokes antidromic firing inducing F‐waves more consistently compared with PNS.
F‐waves reflect the spinal motoneuron excitability. Peripheral nerve stimulation (PNS) is used to induce F‐waves, whereas an alternative method to activate peripheral nerves, motor point stimulation (MPS), which delivers electrical stimulation over the muscle belly, has never been used. We showed that MPS induced F‐waves in the soleus muscle with higher persistence, larger amplitudes and less pain than ones induced using PNS.
•Spatiotemporal variability during walking is related to increased risk for falls.•Low margin of stability preceded steps with altered length, width, and time.•Margin of stability was preserved at ...heel strike for these steps.•Step variability may reflect efforts to preserve mechanical stability when walking.
Increased variability of spatio-temporal features while walking is related to increased risk of falls. It is thought that variability in foot placement and timing reflects responses to mechanical instability while walking. The purpose of this study was to determine whether ‘extreme’ values of step length, width and time follow transient periods of low mechanical stability during the single support phase of gait in healthy young adults. We conducted secondary analysis of a portion of an existing dataset. Eleven healthy adults walked on an instrumented treadmill. Participants were outfitted with reflective markers and completed two 1-min periods of walking at each of 3 speeds (0.8m/s, 1.2m/s, and 1.6m/s). Margins of stability were calculated relative to the anterior, posterior, lateral, and medial boundaries of the base of support, and the value at heel strike and the minimum value during the first half of each single-support phase were extracted. Step length, swing time, and step width were calculated from motion capture and ground reaction force data. Extreme values for consecutive steps were identified using Poincaré plots, and margins of stability in each direction were compared between ‘normal’ and ‘extreme’ steps. Margins of stability in both the anterior and medial direction were lower prior to long and wide steps, respectively. Margins of stability in the anterior and medial directions were lower prior to quick steps, and margins of stability in the posterior and lateral directions were lower prior to slow steps. There were either no significant differences in margin of stability between ‘normal’ and ‘extreme’ steps at heel strike, or the direction of the relationship was reversed to that observed during single support. These data suggest that spatio-temporal variability may reflect adjustments in step placement and timing to compensate for transient periods of low mechanical stability when walking.
It is well known that a light and voluntary touch with a fingertip on a fixed surface improves postural stability during quiet standing. To determine whether the effect of the light touch is due to ...the tactile sensory input, as opposed to mechanical support, we investigated the light touch effect on postural stability during quiet standing with and without somatosensory input from the fingertip. Seven young subjects maintained quiet standing on a force platform with (LT) and without (NT) lightly touching a fixed surface, and with (TIS) and without (CON) the application of tourniquet ischemia, which removed the tactile sensation from the fingertip. The mean velocity of centre of pressure (CoP) was calculated to assess the postural sway in each condition. The mean velocity of CoP was significantly smaller in the LT condition compared to the NT condition only under the CON condition, whereas the light touch effect was not significant under the TIS condition. We found that the reduction of the horizontal ground reaction force due to the light touch was about 20%, which was approximately equivalent to the reduction of mean velocity of CoP in the LT condition compared to the NT condition. Since the fingertip contact force was relatively large compared to the horizontal ground reaction force, one could say that the light touch effect might be due to the mechanical support provided by the contact itself. However, we demonstrated experimentally that light touch effects were diminished due to loss of finger tactile feedback induced by the tourniquet ischemia, but not due to the mechanical support provided by the light touch. One possible reason is the lack of feedback information in controlling posture, and the other is the altered control of the arm induced by the loss of tactile feedback.
We investigated age-related differences in the required coefficient of friction (RCOF) during 90° turning, the difference of RCOF during step and spin turn, and how affects observed differences. ...Sixteen healthy young and healthy older adults (eight men and eight women in each group) participated. Participants performed 90° step and spin turns to the right at a self-selected normal speed. Older adults turned with lower RCOF than the young adults during both step and spin turns. This was associated with reduced mediolateral (ML) RCOF component (RCOFML) for the older adults. Reduced RCOFML in older adults was associated with reductions in the ML component of the lean angle of the body during turning. This age-related gait changes during turning can be compensatory mechanisms that allowed older adults to turn while reducing the risk of slipping. Spin turns exhibited lower RCOF, resulting from significantly lower RCOFML, than step turns in young and older adults; thus, spin turning is a safer turning strategy for preventing lateral slips. This may suggest that, in older adults, slip prevention may take precedence over balance recovery after slips sustained during turning. These results illustrate a turning gait mechanism that helps prevent slips and falls, and how age affects this mechanism.
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