Accuracy of spring-levered and piezo-electric pedometers in primary school Japanese children

Pedometers are used in many studies because physical activities can be simply assessed using them. In addition to the spring-levered type, piezo-electric pedometers have recently been used. However, their accuracy in children has not been investigated in previous studies. In this study, we investigated the accuracy of spring-levered pedometer and piezo-electric pedometer step counts in comparison with hand-tallied step counts with children during self-paced walking. First to 6th-grade primary school children (394 subjects; 201 boys and 193 girls) walked with pedometers on an outdoor 50-m course, and the measured values were compared with actual steps at 3 speeds: normal, slow, and fast paces. The counts obtained by the spring-levered pedometer were significantly lower than the actual steps in most grades at all walking paces. In the normal- and fast-pace walking, the counts by spring-levered pedometer were significantly lower than the actual steps in all grades excluding the 5th grade. Moreover, the spring-levered pedometer underestimated by 25% or more in all grades at slow pace. In contrast, the percent error of the counts by the piezo-electric pedometers at normal pace were mostly within +/-3%, confirming their high accuracy. Based on these findings, spring-levered pedometers are not appropriate for children, whereas piezo-electric pedometers are useful for investigation of the physical activity of children.     

Step Detection and Activity Recognition Accuracy of Seven Physical Activity Monitors

The aim of this study was to compare the seven following commercially available activity monitors in terms of step count detection accuracy: Movemonitor (Mc Roberts), Up (Jawbone), One (Fitbit), ActivPAL (PAL Technologies Ltd.), Nike+ Fuelband (Nike Inc.), Tractivity (Kineteks Corp.) and Sensewear Armband Mini (Bodymedia). Sixteen healthy adults consented to take part in the study. The experimental protocol included walking along an indoor straight walkway, descending and ascending 24 steps, free outdoor walking and free indoor walking. These tasks were repeated at three self-selected walking speeds. Angular velocity signals collected at both shanks using two wireless inertial measurement units (OPAL, ADPM Inc) were used as a reference for the step count, computed using previously validated algorithms. Step detection accuracy was assessed using the mean absolute percentage error computed for each sensor. The Movemonitor and the ActivPAL were also tested within a nine-minute activity recognition protocol, during which the participants performed a set of complex tasks. Posture classifications were obtained from the two monitors and expressed as a percentage of the total task duration.The Movemonitor, One, ActivPAL, Nike+ Fuelband and Sensewear Armband Mini underestimated the number of steps in all the observed walking speeds, whereas the Tractivity significantly overestimated step count. The Movemonitor was the best performing sensor, with an error lower than 2% at all speeds and the smallest error obtained in the outdoor walking. The activity recognition protocol showed that the Movemonitor performed best in the walking recognition, but had difficulty in discriminating between standing and sitting. Results of this study can be used to inform choice of a monitor for specific applications.     

A wearable solution for accurate step detection based on the direct measurement of the inter-foot distance

Accurate step detection is crucial for the estimation of gait spatio-temporal parameters. Although several step detection methods based on the use of inertial measurement units (IMUs) have been successfully proposed, they may not perform adequately when the foot is dragged while walking, when walking aids are used, or when walking at low speed. The aim of this study was to test an original step-detection method, the inter-foot distance step counter (IFOD), based on the direct measurement of the distance between feet. Gait data were recorded using a wearable prototype system (SWING^2DS), which integrates an IMU and two time-of-flight distance sensors (DSs). The system was attached to the medial side of the right foot with one DS positioned close to the forefoot (FORE_DS) and the other close to the rearfoot (REAR_DS). Sixteen healthy adults were asked to walk over ground for two minutes along a loop, including both rectilinear and curvilinear portions, during two experimental sessions. The accuracy of the IFOD step counter was assessed using a stereo-photogrammetric system as gold standard. The best performance was obtained for REAR_DS with an accuracy higher than 99.8% for the instrumented foot step and 88.8% for the non-instrumented foot step during both rectilinear and curvilinear walks. Key features of the IFOD step counter are that it is possible to detect both right and left steps by instrumenting one foot only and that it does not rely on foot impact dynamics. The IFOD step counter can be combined with existing IMU-based methods for increasing step-detection accuracy.     

Ability of short-time Fourier transform method to detect transient changes in vagal effects on hearts: a pharmacological blocking study

Conventional spectral analyses of heart rate variability (HRV) have been limited to stationary signals and have not allowed the obtainment of information during transient autonomic cardiac responses. In the present study, we evaluated the ability of the short-time Fourier transform (STFT) method to detect transient changes in vagal effects on the heart. We derived high-frequency power (HFP, 0.20-0.40 Hz) as a function of time during active orthostatic task (AOT) from the sitting to standing posture before and after selective vagal (atropine sulfate 0.04 mg/kg) and sympathetic (metoprolol 0.20 mg/kg) blockades. The HFP minimum point during the first 30 s after standing up was calculated and compared with sitting and standing values. Reactivity scores describing the fast and slow HFP responses to AOT were calculated by subtracting the minimum and standing values from the sitting value, respectively. The present results, obtained without controlled respiration, showed that in the drug-free condition, HFP decreased immediately after standing up (P < 0.001) and then gradually increased toward the level characteristic for the standing posture (P < 0.001), remaining lower than in the sitting baseline posture (P < 0.001). The magnitudes of the fast and slow HFP responses to AOT were abolished by the vagal blockade (P < 0.001) and unaffected by the sympathetic blockade. These findings indicate that HFP derived by the STFT method provided a tool for monitoring the magnitude and time course of transient changes in vagal effects on the heart without the need to interfere with normal control by using blocking drugs.     

Estimating daily walking distance of captive African elephants using an accelerometer

Two central concerns for elephant husbandry and management are whether zoological enclosures are appropriately sized and the degree to which naturalistic exercise and activity are observed in such enclosures. In order to address these issues, accurate data on the daily walking distance of elephants both in situ and ex situ are necessary. We used an accelerometer, a pedometer that measures step count and activity level, to estimate walking distance in African elephants (Loxodonta africana) at the San Diego Zoo's Wild Animal Park. The accelerometer was worn simultaneously with a GPS unit that recorded actual walking distance. Estimates of walking distance were extrapolated from the accelerometer and compared with actual distances determined by GPS data. The accelerometer was found to overestimate step count, and subsequently walking distance, by including false counts of steps. Extrapolating walking distance based upon stride length measurements did not match actual GPS walking distance. However, activity level output from the accelerometer significantly correlated with actual GPS walking distance. In addition, we report that the rate of movement is comparable to that reported in other zoological settings. We provide a linear regression equation that can be utilized by other institutions to estimate daily walking distance of elephants in their collection who are outfitted with accelerometers.     

Pedometer readings for estrous detection and as predictor for time of ovulation in dairy cattle

The objective of this study was to study the relationship between increase in number of steps measured by pedometers, behavioral estrous parameters and time of ovulation, in order to investigate whether the number of steps can be used as a tool for estrous detection and as a predictor for time of ovulation. In total, 63 ovulations were observed in 43 Holstein-Friesian cows. Different behavioral signs of estrus were observed at 3h intervals. Cows were equipped with pedometers, which stored number of steps in 2h time periods and pedometer estrus alerts were defined using different algorithms and thresholds. The percentage of behavioral estruses also detected by pedometers measurements, ranged between 51 and 87% for all estrous periods. When only estrous periods where taken into account in which more than one animal was in estrus, detection percentages increased up to 95%. Number of steps taken during the estrous period was higher when more animals were in behavioral estrus at the same time, and number of steps taken during the estrous period was also higher for primiparous cows compared to multiparous cows. Ovulation occurred 29.3+/-3.9h after onset of increased number of steps (ranging between 39 and 22 h) and 19.4+/-4.4h after the end of increased number of steps (ranging between 35 and 12h). The intervals were not influenced by the number of animals that were in estrus at the same time or by parity. In conclusion, pedometers can detect estrus accurately and appear to be a promising tool for prediction of ovulation and hence could be a tool for improving fertilization rates.     

Can Insulated Skin Temperature Act as a Substitute for Rectal Temperature when Studying Circadian Rhythms?

We measured rectal, lateral chest wall, and axillary temperature every half hour for at least 24 h while subjects were living normal life-styles and keeping a sleep/activity diary. We then used a purification method to estimate the decrease of temperature due to sleep and the increases due to sitting, standing, walking, or exercising, as well as the parameters of the cosine curve that described the “purified data.” Cosinor analysis of raw and purified data showed that the acrophases from both skin sites were much more variable and up to 8 h later than were those from the rectum (particularly if exercise had been taken), even though the acrophases from the two skin sites were similar to each other. For rectal temperature, there was an increase in the size of the masking effect as activity progressed through the sequence: sitting, standing or walking, exercising. In contrast, for both chest wall and axillary temperatures, although sitting produced masking effects similar to those for rectal temperature, masking effects due to standing or walking and exercising were much smaller, and sometimes they were even less than the masking effects due to sitting. These results indicate that our measurements of cutaneous temperature did not act as a substitute for rectal temperature, particularly when the subject was physically active rather than sedentary.     

Can Insulated Skin Temperature Act as a Substitute for Rectal Temperature when Studying Circadian Rhythms?

We measured rectal, lateral chest wall, and axillary temperature every half hour for at least 24 h while subjects were living normal life-styles and keeping a sleep/activity diary. We then used a purification method to estimate the decrease of temperature due to sleep and the increases due to sitting, standing, walking, or exercising, as well as the parameters of the cosine curve that described the “purified data.” Cosinor analysis of raw and purified data showed that the acrophases from both skin sites were much more variable and up to 8 h later than were those from the rectum (particularly if exercise had been taken), even though the acrophases from the two skin sites were similar to each other. For rectal temperature, there was an increase in the size of the masking effect as activity progressed through the sequence: sitting, standing or walking, exercising. In contrast, for both chest wall and axillary temperatures, although sitting produced masking effects similar to those for rectal temperature, masking effects due to standing or walking and exercising were much smaller, and sometimes they were even less than the masking effects due to sitting. These results indicate that our measurements of cutaneous temperature did not act as a substitute for rectal temperature, particularly when the subject was physically active rather than sedentary.     

Sedentary work and the risks of colon and rectal cancer by anatomical sub-site in the Canadian census health and environment cohort (CanCHEC)

BackgroundSedentary behaviour is a potential risk factor for colorectal cancer. We examined the association between sedentary work, based on body position, and colorectal cancer risk in Canadians.MethodsA working body position category (a. sitting; b. standing and walking; c. sitting, standing, and walking; d. other) was assigned to occupations reported by 1991 Canadian Census respondents based on national occupational counselling guidelines. Adjusted hazard ratios (HRs) and 95% confidence intervals (CI) were estimated for cancers of the colon (overall, proximal, and distal) and rectum in men and women newly diagnosed from 1992 to 2010.ResultsCompared to “sitting” jobs, men in occupations with “other” (non-sitting, −standing, or −walking) body positions had a weakly significant reduced colon cancer risk (HR = 0.93, 95% CI: 0.89, 0.98) primarily attributed to protection at the distal site (HR = 0.90, 95% CI: 0.84, 0.97). Men in “standing and walking” and “sitting, standing, and walking” jobs did not have significantly reduced colon cancer risks. No effects were observed for rectal cancer in men or colon and rectal cancer in women.ConclusionThe two significant findings of this analysis should be followed-up in further investigations with additional information on potential confounders. Null findings for rectal cancer were consistent with other studies.     

Duration and frequency of every day activities in total hip patients.

Little knowledge about frequency and duration of daily activities in patients after total hip arthroplasty is available. Such information is required for the definition of realistic load collectives for pre-clinical testing of prostheses. It could also be helpful for the quantitative evaluation of surgery outcome with different prosthesis types. The purpose of this study was to develop and apply a system for the determination of frequency and duration of patient activities in their habitual environment and to compare the results to a clinical outcome score (Harris hip score).A portable activity monitoring system (weight 1.6 kg including batteries) was designed using a Palm top computer, 2 inclination sensors for the thigh and calf and one goniometer positioned at the knee joint. An algorithm was developed to identify frequency and duration of the activities lying, sitting, standing, walking and stair climbing from the signals of the 3 sensors. 42 patients participated in the study and were equipped with the system in the morning at their home. Datasets of 31 patients (age 62.5+/-11.5 y) covered more than 6h (9.8 +/- 1.6 h) and were included in the analysis. Prosthesis specific data as well as the Harris hip score were collected.The most frequent patient activity was sitting (44.3% of the time), followed by standing (24.5%), walking (10.2%), lying (5.8%) and stair climbing (0.4%). The median number of steps/stairs was 6048/164. The number of step cycles representing one year in vivo use should, consequently, be increased to 1.1 million. The Harris hip score (91.4 +/- 9.8) correlated significantly with the number of stairs (r(2) = 0.26, p = 0.003) and showed a positive tendency with the number of steps per day. No differences in activity levels between prosthesis specific factors were found.     

Accelerometer-based body-position sensing for ambulatory electrocardiographic monitoring

Our objective is to validate the ability of 3 appropriately placed accelerometers to determine body position during ambulatory electrocardiographic (ECG) monitoring and to demonstrate the clinical applicability of this method. During ambulatory (Holter) monitoring, the ability to know a patient's position (lying down, sitting, standing, or changing from one position to another) is important in the evaluation of common symptoms such as dizziness, palpitations, and syncope. Changes in body position are also known to alter the electrical axis of the heart, resulting in artifactual changes in QRS amplitude and ST-segment morphology. We have developed an ambulatory patient-monitoring instrument that, through the use of microfabricated accelerometers, can simultaneously record body-position information and 2 channels of ECG data. The accelerometers measure the effects of gravity and dynamic acceleration, allowing determination of a patient's orientation and movements. The accelerometer and ECG signals are input to a portable recorder and are filtered and digitized. Algorithms were developed to automatically determine body position. Ten healthy volunteers wore the device for 1 hour and followed a protocol of standing, sitting, walking, lying supine, and lying in the left and right lateral decubitus positions. An observer manually recorded times of position changes. Data were recorded and analyzed using software designed with MATLAB. The ability of the accelerometers and computer algorithms to determine body position was analyzed in terms of the sensitivity and specificity for each body position. The sensitivities for sitting, standing, walking, lying supine, lying right, and lying left were 98.8%, 99.2%, 95.5%, 99.1%, 98.9%, and 94.8%, respectively. The specificities were 99.7%, 99.4%, 99.6%, 99.0%, 99.8%, and 99.9%, respectively. The use of microfabricated accelerometers is a clinically feasible method to determine body position and can be applied to future studies correlating body position with ECG or other physiologic data.     

Myosin VI walks hand-over-hand along actin

Myosin VI is a molecular motor that can walk processively on actin filaments with a 36-nm step size. The walking mechanism of myosin VI is controversial because it takes very large steps without an apparent lever arm of required length. Therefore, myosin VI is argued to be the first exception to the widely established lever arm theory. It is therefore critical to directly demonstrate whether this motor walks hand-over-hand along actin despite its short lever arm. Here, we follow the displacement of a single myosin VI head during the stepping process. A single head is displaced 72 nm during stepping, whereas the center of mass previously has been shown to move 36 nm. The most likely explanation for this result is a hand-over-hand walking mechanism. We hypothesize the existence of a flexible element that would allow the motor to bridge the observed 72-nm distance.     

Validation and Reliability of a Classification Method to Measure the Time Spent Performing Different Activities

The aim of this study was to validate the performance and reliability of results obtained from a classification model that measures time spent performing activities in confined (CE) and unrestricted (UE) environments. In CE, participants wore a pair of biaxial and/or triaxial accelerometers while performing pre-determined training activities classified as variants of lying down, dynamic standing, sitting, walking and running on two separate days. A classification model trained with activities performed in a specific order during the first day was developed to validate the activities performed in a random order on the second day (CE) and over 24 hours on a separate day (UE). The performance of the classification model was validated against triaxial accelerometers using six (x, y and step counts for arm and thigh) or eight (same as six features plus z axis) features. The reliability of the classification model was tested in both environments using six features. Results revealed an overall accuracy of 94% in CE and 90% in UE. The sensitivity in CE and UE was 94% and 95% for lying down, 88% and 80% for dynamic standing, 97% and 89% for sitting, 96% and 78% for walking and 90% and 64% for running, respectively. No significant differences were noted between performances obtained with six or eight features. Results were highly reproducible in both environments. The results obtained from the classification model were accurate and reproducible, and highlight the potential use of this approach in research to quantify the time spent performing different activities.     

Motor Learning Characterized by Changing Lévy Distributions

The probability distributions for changes in transverse plane fingertip speed are Lévy distributed in human pole balancing. Six subjects learned to balance a pole on their index finger over three sessions while sitting and standing. The Lévy or decay exponent decreased as a function of learning, showing reduced decay in the probability for large speed steps and was significantly smaller in the sitting condition. However, the probability distribution for changes in fingertip speed was truncated so that the probability for large steps was reduced in this condition. These results show a learning-induced tolerance for large speed step sizes and demonstrate that motor learning in continuous tasks may be characterized by changing distributions that reflect sensorimotor skill acquisition.     

Assessing pedometer accuracy while walking, skipping, galloping, sliding, and hopping

The purpose of this study was to determine the accuracy of the pedometer when walking, skipping, galloping, sliding, and hopping. One hundred-two college students were fitted with a pedometer (Walk4Life LS-7010) at mid-thigh on the right and left of the hip. Participants then performed the randomly assigned movements for the length (26 m) of a hardwood court playing surface, during which time the investigator tallied the steps with a hand counter. Each step with the lead foot elicited a tally on the counter. Participants were instructed to perform the movement at a brisk pace, to jump-stop at the end of the court, and to remain still until after the pedometer reading was recorded. Repeated measure ANOVAs using the Bonferroni technique were used to compare differences between pedometer counts and hand counts. Significant differences were evident between the hand tally counts and readings from the right and left pedometers during all five locomotor movements (P < .01). Mean error was lowest between the hand tally and the average of the right and left pedometers while walking (-1.35 +/- 1.60) and hopping (-2.94 +/- 2.33), and increased while sliding (-6.42 +/- 4.78), galloping (-8.22 +/- 4.63), and skipping (-8.30 +/- 4.45). Results indicate the pedometer may not consistently register the vertical force produced by the trail foot contact, the lead foot contact, or a combination of the two while skipping, galloping, and sliding. Though the pedometer is a valid instrument when estimating physical activity levels, caution is urged when interpreting movements other than walking.     

Suppression of cardiocirculatory responses to orthostatic stress by passive walking-like leg movement in healthy young men

ABSTRACT: BACKGROUND: Although passive walking-like leg movement in the standing posture (PWM) has been used in the clinical field, the safety of PWM has not been fully determined despite the risks of orthostatic intolerance due to standing posture. The aim of the present study was to examine cardiocirculatory response during PWM in healthy young men. METHODS: The subjects (n = 13) spent 5 min in a sitting position and then 5 min in a quiet standing position to determine baseline levels. Thereafter, they underwent 25-min rhythmic PWM at 1 Hz while standing. In another bout, subjects experienced the same protocol except that they underwent 25-min quiet standing (QS) instead of 25-min PWM. Two subjects dropped out of the 25-min QS due to feeling of discomfort. Thus, data obtained in the remaining eleven subjects are presented. RESULTS: In the PWM trial, systolic arterial blood pressure (SAP) decreased from 112 +/- 8 mmHg during the sitting baseline period to 107 +/- 8 mmHg during the standing baseline period (p <0.05), while heart rate (HR) increased from 73 +/- 9 bpm during the sitting baseline period to 84 +/- 10 bpm during the standing baseline period (p <0.001). After the imposition of PWM, SAP increased from 107 +/- 8 mmHg in the standing baseline period to 120 +/- 6 mmHg (p <0.001), while HR decreased from 84 +/- 10 bpm in the standing baseline period to 76 +/- 9 bpm (p <0.05). In the QS trial, SAP, which had decreased during the standing baseline period compared to that during the sitting baseline period, remained lowered during the 25-min QS period, while HR, which had increased during the standing baseline period compared to that during the sitting baseline period, remained elevated during the 25-min QS period. In both bouts, HR showed almost mirror-image changes in the high-frequency component of HR variability, suggesting that the changes in HR were due to change in parasympathetic activation. Double product (HR x SAP), as a predictor of myocardial oxygen consumption, during the 25-min QS period tended to increase with time, but double product remained almost constant during the 25-min PWM period. CONCLUSIONS: The results suggest that PWM is effective for suppressing cardiocirculatory responses to orthostatic stress.     

IMU-based ambulatory walking speed estimation in constrained treadmill and overground walking

This study evaluated the performance of a walking speed estimation system based on using an inertial measurement unit (IMU), a combination of accelerometers and gyroscopes. The walking speed estimation algorithm segments the walking sequence into individual stride cycles (two steps) based on the inverted pendulum-like behaviour of the stance leg during walking and it integrates the angular velocity and linear accelerations of the shank to determine the displacement of each stride. The evaluation was performed in both treadmill and overground walking experiments with various constraints on walking speed, step length and step frequency to provide a relatively comprehensive assessment of the system. Promising results were obtained in providing accurate and consistent walking speed/step length estimation in different walking conditions. An overall percentage root mean squared error (%RMSE) of 4.2 and 4.0% was achieved in treadmill and overground walking experiments, respectively. With an increasing interest in understanding human walking biomechanics, the IMU-based ambulatory system could provide a useful walking speed/step length measurement/control tool for constrained walking studies.     

IMU-based ambulatory walking speed estimation in constrained treadmill and overground walking

This study evaluated the performance of a walking speed estimation system based on using an inertial measurement unit (IMU), a combination of accelerometers and gyroscopes. The walking speed estimation algorithm segments the walking sequence into individual stride cycles (two steps) based on the inverted pendulum-like behaviour of the stance leg during walking and it integrates the angular velocity and linear accelerations of the shank to determine the displacement of each stride. The evaluation was performed in both treadmill and overground walking experiments with various constraints on walking speed, step length and step frequency to provide a relatively comprehensive assessment of the system. Promising results were obtained in providing accurate and consistent walking speed/step length estimation in different walking conditions. An overall percentage root mean squared error (%RMSE) of 4.2 and 4.0% was achieved in treadmill and overground walking experiments, respectively. With an increasing interest in understanding human walking biomechanics, the IMU-based ambulatory system could provide a useful walking speed/step length measurement/control tool for constrained walking studies.     

Nordic Walking improves daily physical activities in COPD: a randomised controlled trial

Background

In patients with COPD progressive dyspnoea leads to a sedentary lifestyle. To date, no studies exist investigating the effects of Nordic Walking in patients with COPD. Therefore, the aim was to determine the feasibility of Nordic Walking in COPD patients at different disease stages. Furthermore we aimed to determine the short- and long-term effects of Nordic Walking on COPD patients'' daily physical activity pattern as well as on patients exercise capacity.

Methods

Sixty COPD patients were randomised to either Nordic Walking or to a control group. Patients of the Nordic Walking group (n = 30; age: 62 ± 9 years; FEV₁: 48 ± 19% predicted) underwent a three-month outdoor Nordic Walking exercise program consisting of one hour walking at 75% of their initial maximum heart rate three times per week, whereas controls had no exercise intervention. Primary endpoint: daily physical activities (measured by a validated tri-axial accelerometer); secondary endpoint: functional exercise capacity (measured by the six-minute walking distance; 6MWD). Assessment time points in both groups: baseline, after three, six and nine months.

Results

After three month training period, in the Nordic Walking group time spent walking and standing as well as intensity of walking increased (Δ walking time: +14.9 ± 1.9 min/day; Δ standing time: +129 ± 26 min/day; Δ movement intensity: +0.40 ± 0.14 m/s²) while time spent sitting decreased (Δ sitting time: -128 ± 15 min/day) compared to baseline (all: p < 0.01) as well as compared to controls (all: p < 0.01). Furthermore, 6MWD significantly increased compared to baseline (Δ 6MWD: +79 ± 28 meters) as well as compared to controls (both: p < 0.01). These significant improvements were sustained six and nine months after baseline. In contrast, controls showed unchanged daily physical activities and 6MWD compared to baseline for all time points.

Conclusions

Nordic Walking is a feasible, simple and effective physical training modality in COPD. In addition, Nordic Walking has proven to positively impact the daily physical activity pattern of COPD patients under short- and long-term observation.

Clinical trial registration

Nordic Walking improves daily physical activities in COPD: a randomised controlled trial - ISRCTN31525632     

Lameness detection via leg-mounted accelerometers on dairy cows on four commercial farms

Lameness in dairy herds is traditionally detected by visual inspection, which is time-consuming and subjective. Compared with healthy cows, lame cows often spend longer time lying down, walk less and change behaviour around feeding time. Accelerometers measuring cow leg activity may assist farmers in detecting lame cows. On four commercial farms, accelerometer data were derived from hind leg-mounted accelerometers on 348 Holstein cows, 53 of them during two lactations. The cows were milked twice daily and had no access to pasture. During a lactation, locomotion score (LS) was assessed on average 2.4 times (s.d. 1.3). Based on daily lying duration, standing duration, walking duration, total number of steps, step frequency, motion index (MI, i.e. total acceleration) for lying, standing and walking, eight accelerometer means and their corresponding coefficient of variation (CV) were calculated for each week immediately before an LS. A principal component analysis was performed to evaluate the relationship between the variables. The effects of LS and farm on the principal components (PC) and on the variables were analysed in a mixed model. The first four PC accounted for 27%, 18%, 12% and 10% of the total variation, respectively. PC1 corresponded to Activity variability due to heavy loading by five CV variables related to standing and walking. PC2 corresponded to Activity level due to heavy loading by MI walking, MI standing and walking duration. PC3 corresponded to Recumbency due to heavy loading by four variables related to lying. PC4 corresponded mainly to Stepping due to heavy loading by step frequency. Activity variability at LS4 was significantly higher than at the lower LS levels. Activity level was significantly higher at LS1 than at LS2, which was significantly higher than at LS4. Recumbency was unaffected by LS. Stepping at LS1 and LS2 was significantly higher than at LS3 and LS4. Activity level was significantly lower on farm 3 compared with farms 1 and 2. Stepping was significantly lower on farms 1 and 3 compared with farms 2 and 4. MI standing indicated increased restlessness while standing when cows increased from LS3 to LS4. Lying duration was only increased in lame cows. In conclusion, Activity level differed already between LS1 and LS2, thus detecting early signs of lameness, particularly through contributions from walking duration and MI walking. Lameness detection models including walking duration, MI walking and MI standing seem worthy of further investigation.