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PubMed1977

Oxygen uptake transients at the onset and offset of arm and leg work.

The halftimes (t1/2) of the VO2 on-and off-responses have been determined on 4 moderately active subjects (1) in arm cranking (VO2 congruent to 1 1/min). (2) in leg pedaling at 4 graded submaximal (VO2 congruent to 0.8 to 2.51/min) work loads, and (3) when superimposing arm cranking on preexisting leg pedaling, both in the supine and in the upright position. In supine experiments the mean t1/2 of the VO2 on-response was longer for arm cranking than for leg pedaling (64 vs 44-49 sec) at equal VO2; however, at the same percentage of arm and leg VO2 max the respective t1/2 were similar. In sitting experiments all t1/2 of the VO2 on-response were shorter than when supine, but the t1/2 for the arms were still slightly longer than those for the legs. When arm cranking was superimposed on preexisting leg pedaling, the t1/4 for arms was reduced both in supine (from 64 to 35-38 sec) and in the sitting position (from 44 to 40 sec). The halftime of the VO2 off-response were much shorter (20-32 sec) than those of the on-response and similar in all experiments. In all conditions the O2 deficits at work onset were considerably larger than the fast component of the corresponding O2 debts during the first minutes of recovery. The difference was totally accounted for by anaerobic glycolysis occurring early during the VO2 on-response, particularly in arm exercise. It is concluded that at submaximal work loads the O2 deficit is accounted for the fast component of the O2 debt plus the O2 equivalent of the early lactate production.

Adult↗
PubMed2005

Plantar feedback contributes to the regulation of leg stiffness.

BACKGROUND: Running and hopping involve moving in a bouncing fashion during which the limbs behave as springs. The ability to alter the stiffness of these leg springs is essential to maintaining an efficient gait. Since the plantar surface of the foot is the only part of the body to encounter the ground during bipedal locomotion, it would seem logical that some aspect of the neurological functioning of the foot is responsible for transmission of information about the surface characteristics to the central nervous system, resulting in changes in leg stiffness. METHODS: Ten subjects (9 males, 1 female) participated in this experiment. Lidocaine was injected inferior and posterior to the lateral malleolus in order to achieve tibial nerve block at the level of the ankle. Subjects hopped at 2.2 Hz on a force plate while data were collected at 1000 Hz. Data were analyzed for peak force and leg stiffness and compared using a repeated measures ANOVA. FINDINGS: Tactile sensation, deep pressure sensation, and abductor hallucis activity displayed significant decreases following the injection, as did postural stability. Subjects demonstrated a significantly decreased leg stiffness after the nerve block (P<.01). INTERPRETATION: Plantar sensation has an effect on regulating leg mechanics in hopping. A loss of sensation in this region can exert a significant impact on the properties of the leg in gait, and future research should determine the specific pathways by which plantar feedback exerts this effect.

Adult↗
PubMed2004

Cerebellar activation during leg withdrawal reflex conditioning: an fMRI study.

OBJECTIVE: The aim of the present study was to examine cerebellar areas related to conditioning of the nociceptive leg withdrawal reflex using event-related functional magnetic resonance imaging (fMRI). Because of the aversive nature of the unconditioned stimulus effects of accompanying fear conditioning were expected. METHODS: In 20 healthy adult subjects leg withdrawal reflex conditioning was performed using a standard delay protocol during MR-scanning. Electromyographic recordings from the anterior tibial and biceps femoris muscles were used to quantify conditioned responses. Fear-related changes of heart rate were assessed. RESULTS: In the group of all subjects a significant increase of cerebellar activation was found in the anterior and posterior vermis. In the group of subjects (n=9) who showed conditioned leg withdrawal responses cerebellar activation was more pronounced in parts of the anterior vermis, which correspond to the known leg representation. In the group of subjects (n=11) who did not develop conditioned responses cerebellar activation was more pronounced in the posterolateral hemispheres. Changes of heart rate, however, did not significantly differ between groups. CONCLUSIONS: Results suggest that areas within the anterior vermis are involved in conditioning of the leg withdrawal response. The present results, however, do not allow to differentiate between motor performance, learning or timing-related processes. Areas in the posterior vermis and cerebellar hemispheres may be related to concomitant fear conditioning. SIGNIFICANCE: Results of the present event-related fMRI study suggest involvement of the human cerebellum in conditioning of the nociceptive leg withdrawal response.

Adult↗
PubMed2005

Cardiovascular variability during periodic leg movements: a spectral analysis approach.

OBJECTIVE: Changes in cardiovascular measures have been advocated as sensitive markers of phasic events arising from sleep. The current study was aimed to analyse the effects of periodic leg movements (PLMS) on heart rate variability (HRV) during NREM sleep in patients having restless legs syndrome and periodic leg movements during sleep. METHODS: The absolute and normalized high- and low-frequency peaks from spectral analysis (FFT) of R-R intervals, the HRV changes using wavelet transform, the geometric and time domain HRV were measured in 14 patients with restless legs syndrome and PLMS. The analysis was done comparing one hundred, 10 min periods with PLMS (PLMS+) and 60 periods without PLMS (PLMS-) in stage 2 of NREM sleep. In 8 patients analysis was also done in slow wave sleep (SWS). RESULTS: Occurrence of PLMS induced changes in geometrical indices of HRV, with a rise of the triangular index and the triangular interpolation of R-R intervals in PLMS+ periods (P < 0.0001). Small changes in time domain indices were found during PLMS+ periods, while the SD of the R-R intervals (SDNN), reflecting global HRV, was significantly higher (P = 0.001). While the low frequency (LF) power significantly increased in PLMS+ periods (P < 0.0001), high frequency (HF) power showed a weak and not significant reduction. The rise in sympathetic activity as detected by frequency domain HRV analysis was related to density and interval of PLMS. Comparison between sleep stages of NREM sleep demonstrated lower values of HRV measures when PLMS+ periods occur in SWS. CONCLUSIONS: Overall, PLMS occurrence was associated with a shift to increased sympathetic activity without significant changes in cardiac parasympathetic activity. The frequency domain analysis of HRV appears to be an easy tool to estimate the autonomic changes related to PLMS and PLMS- arousals and to differentiate their occurrence during stage 2 and deep sleep. SIGNIFICANCE: Spectral HRV measures may offer a simple approach to estimate the degree of autonomic changes occurring in relation to periodic leg movements in restless legs patients.

Adult↗
PubMed2006

Ulcer-related problems and health care needs in patients with venous leg ulceration: a descriptive, cross-sectional study.

BACKGROUND: Patients with leg ulceration often have long lasting and recurrent wounds. The treatment exists mainly of wound-care and compression therapy. International literature shows several indications of problems in relation to leg ulceration, but no studies were performed to give a comprehensive overview of all problems identified and care received related to these problems. OBJECTIVES: The aim of the study was to describe leg ulcer-related problems in patients with leg ulcers based on venous insufficiency or a mixed aetiology. Furthermore, an inventory of current care and care deficits in the care for leg ulcer patients was made. METHODS: The study had a descriptive, cross-sectional design. A sample of 141 patients was taken from the population of outpatient clinics of seven hospitals in the Netherlands. Data were collected through patient interviews, questionnaires and wound-observations. Medical information was provided by the dermatologist or derived from the patients' medical file. RESULTS: The study identified a number of serious problems. Main problems were pain (85%), outdoor mobility (47%) and problems in finding appropriate footwear (60%). Statistical analysis showed no differences between patients with ulcers based on a venous aetiology and ulcers based on mixed aetiology. Fifty to seventy percent of the patients did not receive any care in relation to these problems. Only a rather small proportion of the patients, however, regarded the help as insufficient. CONCLUSION: Care at outpatient clinics is mainly focused on wound care and compression therapy. Pain treatment and care related to problems encountered by patients appears to be insufficient. This is not only affecting the patient's quality of life, but is likely to affect also the healing process and prevention of leg ulcers. Nurses and dermatologist should take their responsibilities in this matter.

Adult↗
PubMed2006

Changes in blood coagulation of arm and leg veins during a simulated long-haul flight.

INTRODUCTION: Long-haul flights are associated with an increased incidence for venous thromboembolic events. At present, markers of coagulation and fibrinolysis were only analyzed from arm veins after long distance travel. Respective data from leg veins are missing. MATERIALS AND METHODS: Here, we measured these parameters in healthy volunteers (n=12) before and after 10 h sitting in modern aircraft chairs under normobaric hypoxia (corresponding to 2400 m altitude). Blood was collected from arm and leg veins before, immediately after and 1 day after sitting in the hypoxic chamber. RESULTS: We did not find any evidence for a significant intravasal thrombin and fibrin formation and a changed fibrinolytic activity, neither in arm nor in leg vein blood. TAT, PAP, and PAI-1 remained unchanged, and the increases of F1+2 in arm veins and of d-dimer in leg veins were within the upper reference limits. Moreover, there was no evidence of activation of coagulation as measured by thrombelastography (ROTEM(R)) and the new Thrombin Dynamic Test at both locations. There was no evidence of arm or leg hemoconcentration. CONCLUSIONS: In healthy volunteers, prolonged sitting in ergonomically superior aircraft seats does not induce significant changes in blood coagulation and fibrinolysis in venous blood of arm or leg. Since this study was performed under moderate hypoxia, reduction in oxygen pressure seems not to be a crucial factor for venous thrombosis at long-haul flights.

Adult↗
PubMed2002

3D whole body scanning to determine mass properties of legs.

We describe a novel method of measuring the mass properties of the limbs, specifically legs. We use the method to obtain the mass and centre of mass of the legs which enables us to calculate the leg joint moments from measurements of ground reaction forces using force plates. The data are obtained by using a 3D whole body scanner to obtain a data set representing the surface of both legs. The bones are significantly denser than the soft tissue so their mass is calculated. Textbook values for the densities of bone and soft tissue are used. The actual bones are approximated by stretching appropriate bone shapes to fit the X-ray of the subject. Numerical integration is then used to obtain the mass and centre of mass of the limb. The system is fast and reliable and allows an individual's mass properties to be measured rather than relying upon population surveys which may be biased, particularly, when the subject is atypical by being disabled. Paraplegics can be measured in the scanner using a modified Oswestry standing frame. When compared with a water displacement method, for 10 legs the errors in the total leg volume using this method are less than 1% and in the location of the centre of mass are less than 4%.

Anthropometry↗
PubMed1999

Intensity of leg and arm training after primary middle-cerebral-artery stroke: a randomised trial.

BACKGROUND: We investigated the effects of different intensities of arm and leg rehabilitation training on the functional recovery of activities of daily living (ADL), walking ability, and dexterity of the paretic arm, in a single-blind randomised controlled trial. METHODS: Within 14 days after stroke onset, 101 severely disabled patients with a primary middle-cerebral-artery stroke were randomly assigned to: a rehabilitation programme with emphasis on arm training; a rehabilitation programme with emphasis on leg training; or a control programme in which the arm and leg were immobilised with an inflatable pressure splint. Each treatment regimen was applied for 30 min, 5 days a week during the first 20 weeks after stroke. In addition, all patients underwent a basic rehabilitation programme. The main outcome measures were ability in ADL (Barthel index), walking ability (functional ambulation categories), and dexterity of the paretic arm (Action Research arm test) at 6, 12, 20, and 26 weeks. Analyses were by intention to treat. FINDINGS: At week 20, the leg-training group (n=31) had higher scores than the control group (n=37) for ADL ability (median 19 [IQR 16-20] vs 16 [10-19], p<0.05), walking ability (4 [3-5] vs 3 [1-4], p<0.05), and dexterity (2 [0-56] vs 0 [0-2], p<0.01). The arm-training group (n=33) differed significantly from the control group only in dexterity (9 [0-39] vs 0 [0-2], p<0.01). There were no significant differences in these endpoints at 20 weeks between the arm-training and leg-training groups. INTERPRETATION: Greater intensity of leg rehabilitation improves functional recovery and health-related functional status, whereas greater intensity of arm rehabilitation results in small improvements in dexterity, providing further evidence that exercise therapy primarily induces treatment effects on the abilities at which training is specifically aimed.

Activities of Daily Living↗
PubMed2002

The use of a leg holder immobilisation device in 3D-conformal radiation therapy of prostate cancer.

BACKGROUND AND PURPOSE: To evaluate the impact of a leg holder immobilisation device on patient positioning accuracy in the treatment of prostate cancer. MATERIAL AND METHODS: Twenty patients of similar age and stage of disease treated with curative external beam radiotherapy for prostate cancer were included prospectively. Ten patients were sequentially allocated to one of the two groups, and treated either with or without a leg holder. Treatment set-up alignment accuracy was assessed with an electronic portal imaging device (EPID). RESULTS: Set-up accuracy was 0.3, 0.3 and 0.2 cm for patients with a leg holder, and 0.3, 0.4 and 0.2 cm for patients without a leg holder in the cranio-caudal, anterior-posterior and in the lateral positions, respectively. The difference is not significant. The repositioning accuracy of combined (sagittal and lateral) in-plane rotations on the other hand, was significantly improved with a leg holder device (P = 0.04). CONCLUSIONS: Set-up accuracy can be improved using a leg holder immobilisation device in terms of rotational movement accuracy, thus making on-line corrections more accurate using EPID in the treatment of prostate cancer.

Aged↗
PubMed1996

Leukocyte migration in the leg in response to experimental venous hypertension.

PURPOSE: Leukocyte trapping and activation in the microcirculation of the legs may play an important role in causing skin damage in venous disease. Leukocyte emigration from the microcirculation and subsequent locomotion in response to venous hypertension was studied in a group of 12 normal volunteers using a "skin window" technique. METHODS: Two 0.5-cm square dermal abrasions were made with a dental stone over the gaiter area of the leg and the flexor aspect of the forearm (control), which were covered with moist micropore membranes. The volunteers lay supine for 30 minutes, and then stood supported for 30 minutes to raise the venous pressure in the leg, and then lay supine again for 30 minutes. The experiment was repeated in six volunteers who lay supine for the whole period. The membranes were changed and collected every 15 minutes, fixed in formal saline solution, and dual-stained for monocytes and polymorphonuclear leukocytes. The type and numbers of cells that emigrated and the furthest distance traveled (leading front) by the cells through the membrane were measured. RESULTS: Both in arms and legs, the vast majority of cells that emigrated were neutrophils, with very few monocytes (arm, 93% neutrophils and 7% monocytes; leg, 97% neutrophils and 3% monocytes). In the 30 minutes after venous hypertension, leukocyte migration significantly decreased in the leg (median leukocyte locomotion: basal, 75.3 microns; standing, 73.5 microns; after hypertension, 62.9 microns; p = 0.012, Wilcoxon matched pairs signed rank test), but not in the arm (basal, 86.2 microns; standing, 84.4 microns; after hypertension, 85.5 microns; p = NS) or when the experiment was repeated with the volunteers lying supine for the entire period (basal, 91.5 microns; standing, 89.4 microns; after hypertension, 92.6 microns; p = NS). CONCLUSIONS: Leukocyte migration is decreased immediately after experimental venous hypertension, which may be a result of the release of factors that inhibit migration.

Adult↗
PubMed1998

Fate of the contralateral leg after infrainguinal bypass.

PURPOSE: To identify variables predictive of the need for future vascular intervention in a leg contralateral to one currently undergoing infrainguinal bypass. METHODS: We reviewed the records of 450 consecutively treated patients undergoing infrainguinal bypass for occlusive disease to examine the outcome of a previously untreated contralateral leg. Patients with coexistent contralateral limb-threatening ischemia at the time of initial ipsilateral operation were excluded, as were patients with bilateral disease who underwent a staged contralateral procedure within 3 months of the ipsilateral operation. This yielded a study cohort of 383 patients with no anticipated intervention in the contralateral leg who were followed for a mean value of 38 months. Patient survival and subsequent intervention in the contralateral leg were examined with life-table and regression analysis. RESULTS: Mean age of the patients was 68 years; 60% were men; 54% had diabetes; and 50% had coronary artery disease. The initial ipsilateral operation was performed for limb threat in 90% of instances. Twenty percent of patients subsequently needed intervention in the contralateral leg (infrainguinal bypass 83%, primary major amputation 17%). According to life-table analysis, 30% of patients needed intervention at 5 years, and the overall survival rate was 51% at 5 years. Multivariate analysis indicated that the need for future contralateral intervention was independently predicted with the following four risk factors: diabetes (relative risk [RR] 2.4x), coronary artery disease (RR 1.8x), lower initial ankle-brachial index (RR 2.1x with ankle-brachial index less than 0.7), and younger age (RR 2.2x if age less than 70 years). Regression models predicted the need for contralateral intervention for only 8% of patients at 5 years when none of these risk factors was present but for 67% when all risk factors were present. CONCLUSION: The fate of the contralateral leg after infrainguinal bypass is affected by diabetes, coronary artery disease, contralateral ankle-brachial index, and age at initial ipsilateral bypass. The effect of these risk factors is additive in prediction of the likelihood of future intervention. Knowledge of these factors may help identify instances in which the contralateral greater saphenous vein will be important for future limb salvage and also determine which patients need more careful follow-up care.

Adult↗
PubMed1998

Leg versus forearm flow: 24 h monitoring in 14 normotensive subjects and in 14 age-matched hypertensive patients confined to bed.

A circadian blood pressure rhythm has been demonstrated in the majority of subjects, even if inactive during daytime. A rhythm of leg blood flow and peripheral resistance, with higher values during sleep than during waking, has also been recently shown in subjects confined to bed. Doubts still persist on whether such a rhythm also exists in the forearm, and whether or not its trend is similar to that found in the leg. In this study, leg and forearm blood flow and resistance were monitored noninvasively every 15 min for 22 h in 14 normotensives and 14 age-matched hypertensives confined to bed. A significant blood pressure fall (normotensives, -4.8%/-6.1%; hypertensives, -7.1%/-6.3%; all P <.0001), heart rate decrease (-14.9 in the former, -10% in the latter; both P <.0001) and leg flow increase (normotensives, +47.4%, hypertensives, +36.1%; both P <.0001) were found during sleep in all subjects, because of a blood redistribution probably attributable to activation of the cholinergic system. Forearm flow was significantly higher during sleep (+26.1%, P <.0001) in the normotensives, whereas in the hypertensives a slight nocturnal decrease (-1.9%) was found. In conclusion, the hypertensives had lower leg and forearm flow than the normotensives during sleep and similar during daytime. Peripheral resistance measured in the leg and in the forearm was greater in the former than in the latter, both during sleep and during waking.

Blood Pressure↗
PubMed1992

Aetiology of chronic leg ulcers.

This study was undertaken to determine the relative prevalence of the factors causing chronic ulceration of the leg in the general population. Two hundred and fifty-nine patients with chronic ulceration of the leg were found on screening a Western Australian population of 238,000. (The prevalence of chronic ulceration of the leg was 1.1 per 1000 population.) Two hundred and forty-two of these patients (93%) with 286 chronically ulcerated limbs were fully assessed to determine the factors contributing to ulceration. In 239 limbs (84%) ulceration involved the leg; in these limbs venous disease was the most prevalent cause of ulceration (160 limbs). Arterial disease was found in 66 limbs, with both venous and arterial disease present in 35 limbs. Rheumatoid arthritis was a causative factor in 27 limbs and diabetes was found with 29 limbs with ulceration involving the leg. In 47 limbs (16%) ulceration was confined to the foot; arterial disease (35 limbs) and diabetes (23 limbs) were the most prevalent causes of ulceration in these limbs. Venous disease was infrequent (three limbs). No disorder of the circulation was found in 48 limbs (20%) with ulceration involving the leg, and in 58 (20%) of all ulcerated limbs. More than one aetiological factor was present in 93 limbs (33%). A cause for ulceration was not found in 10 limbs (3.5%).

Adult↗
PubMed1992

Re-intervention after vascular surgery for critical leg ischaemia.

Re-operation after arterial bypass in the leg is common, may be seen as failure by many and can appear expensive to budget holders. Secondary reconstruction may not be undertaken for these reasons. The indications for and outcome of further intervention have been studied in 395 primary presentations with critical leg ischaemia, all of whom underwent arterial reconstruction. During the study period the primary amputation rate was 3%, and 10% of reconstructed patients presented with skin necrosis or gangrene. One hundred and twenty-nine reconstructions (32%) were to crural vessels in the lower third of the calf. Mean follow-up was 3 years, 1 month mortality was 2% and overall mortality 20%. One hundred and seventy-three (44%) patients required further intervention: 118 (30%) for recurrence of ipsilateral ischaemic symptoms and 55 (14%) in the presence of a patent primary graft (mostly operations on the contralateral leg). A total of 695 secondary operations were required over follow-up, a mean 1.75 additional operations per patient per 3 years. Following recurrence of ischaemia, graft revision or secondary revascularisation was undertaken in 98 of 118 (84%) legs whilst the remaining 19 legs had an amputation performed after primary graft failure. Secondary reconstruction was successful in salvaging 63 limbs to mean follow-up, a 64% success rate from revisional surgery. At mean follow-up 339 of 395 limbs remain viable (86% limb salvage), secondary graft patency is 79% and primary graft patency 63%. Failure to re-intervene after primary graft failure would reduce limb salvage at 3 years to 70% with corresponding loss of 63 legs.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1999

The Scottish Leg Ulcer Project.

National and international guidelines on many topics have been introduced in recent years. It is unlikely that the implementation of few, or any, has been evaluated by randomized trial, nor have the impacts of guidelines when combined with training been evaluated. A national guideline produced by the Scottish Intercollegiate Guideline Network (SIGN) entitled 'Management of Chronic Leg Ulcer' was published in July 1998 and this may have influence on care and ultimately healing rates of leg ulcers. The purpose of this paper is to describe the design of a Scottish multi-centre trial and to present baseline data. The Scottish Leg Ulcer Project is a randomized controlled trial which commenced in July 1997 and is designed to compare the impact of the SIGN guideline with the impact of the SIGN guideline reinforced by a formal training programme, on healing rates of leg ulcers. Participants include 16 Scottish community healthcare trusts or health boards, with a population of approximately 2.7 million. Localities have been randomized into control (SIGN guidelines alone) and intervention (SIGN guideline plus a formal training programme). In the intervention localities, link nurses, after intensive training, cascaded similar training to all community staff involved in leg ulcer care. Data are provided by district nurse caseload managers in censuses every three months throughout a six-month baseline and 24-month trial period. The principal endpoint is an ulcer-free leg. The data collection is due to be completed in December 1999, and the project analysed and reported by June 2000.

Adult↗
PubMed1994

[The restless leg syndrome: a condition associated with periodic or aperiodic slowing of the EEG].

There are several new developments with regard to semiology, diagnosis, physiopathology and the treatment of restless leg syndrome (RLS). We present here the hypothesis that motor manifestations of the RLS are synchronous to slowing of the cortical activity as measured by the spectral analysis of the EEG. When the subject is resting in bed with his leg outstretched, slowing of the EEG is observed, which could be periodic at the frequency of approximately 1 every 20 seconds or sustained. Leg movements can be periodic at the frequency of approximately 1 every 20 seconds or sustained. Leg movements can be periodic or aperiodic accordingly. On the contrary, periodic leg movements in sleep (PLMS) occur in close temporal relationship with periodic arousal. These results raised the hypothesis that leg movements (RLS and PLMS) may appear at a critical level of cortical activation. This level is reached during sleepiness in the awake subject or during periodic micro-arousal when the subject is asleep. Other results suggest that these periodic changes in the level of cortical activation may also modulate other abnormal motor behavior in sleep such as rhythmic masticatory muscles activity as seen in sleep bruxism. The same mechanism may also be involved in setting the duration of apneic episodes during slow-wave sleep.

Electroencephalography↗
PubMed2001

Influence of leg stiffness and its effect on myodynamic jumping performance.

The purposes of this study are: a) to examine the possibility of influencing the leg stiffness through instructions given to the subjects and b) to determine the effect of the leg stiffness on the mechanical power and take-off velocity during the drop jumps. A total of 15 athletes performed a series of drop jumps from heights of 20, 40 and 60 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than your previous jump". The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes body positions were recorded using a high speed (250 Hz) video camera. EMG was used to measure muscle activity in five leg muscles. The data was divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and group 5 the shortest. The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness. Maximum center of mass take-off velocity the can be achieved with different levels of leg stiffness. The mechanical power acting on the human body during the positive phase of the drop jumps had the highest values in group 3. This means that there is an optimum stiffness value for the lower extremities to maximize mechanical power.

Ankle Joint↗
PubMed2002

Gender differences in active musculoskeletal stiffness. Part II. Quantification of leg stiffness during functional hopping tasks.

Leg stiffness was compared between age-matched males and females during hopping at preferred and controlled frequencies. Stiffness was defined as the linear regression slope between the vertical center of mass (COM) displacement and ground-reaction forces recorded from a force plate during the stance phase of the hopping task. Results demonstrate that subjects modulated the vertical displacement of the COM during ground contact in relation to the square of hopping frequency. This supports the accuracy of the spring-mass oscillator as a representative model of hopping. It also maintained peak vertical ground-reaction load at approximately three times body weight. Leg stiffness values in males (33.9+/-8.7 kN/m) were significantly (p<0.01) greater than in females (26.3+/-6.5 kN/m) at each of three hopping frequencies, 3.0, 2.5 Hz, and a preferred hopping rate. In the spring-mass oscillator model leg stiffness and body mass are related to the frequency of motion. Thus male subjects necessarily recruited greater leg stiffness to drive their heavier body mass at the same frequency as the lighter female subjects during the controlled frequency trials. However, in the preferred hopping condition the stiffness was not constrained by the task because frequency was self-selected. Nonetheless, both male and female subjects hopped at statistically similar preferred frequencies (2.34+/-0.22 Hz), therefore, the females continued to demonstrate less leg stiffness. Recognizing the active muscle stiffness contributes to biomechanical stability as well as leg stiffness, these results may provide insight into the gender bias in risk of musculoskeletal knee injury.

Adult↗