“It gives me a wake up call” ‐ It is time to implement athlete health monitoring within the Para sport context

OBJECTIVES

The aim of this study was to explore elite Para athletes' and coaches' perceptions of experiences of athlete health monitoring.

MATERIALS AND METHODS

This study used a qualitative design, applying a phenomenographical approach. Thirteen athletes and six coaches from two different socioeconomic contexts (the Swedish and South African Paralympic programs) participated. Data were collected through individual interviews focusing on athletes' and coaches' perceptions of experiences of athlete health monitoring within Para sport.

RESULTS

Three main themes were revealed: (i) the benefits of athlete health monitoring, (ii) the importance of implementation and adaptation of athlete health monitoring in the real-world sports context, and (iii) barriers of athlete health monitoring. The perceptions were that regular monitoring can detect injuries early and thereby prevent them from progressing. Several participants highlighted the importance of monitoring factors beyond injury and illness, such as Para sport-specific health issues. Athletes' experiences were that they started to reflect on their own health, which was interpreted as improvement in health literacy. Another perception was that athlete health monitoring only is conducted within the research context and that athletes are not followed up. The perception was that it is the sports federations' responsibility to monitor and provide support when needed. Lastly, data revealed differences in the possibilities of conducting monitoring, which was related to both socioeconomic factors and Para sport.

CONCLUSION

Coaches and athletes see health monitoring as valuable and important in enhancing athlete health. However, to maximize the impact, the monitoring structure should be specific to the context and provide multidisciplinary support when needed.

Preparing for snow-sport events at the Paralympic Games in Beijing in 2022: recommendations and remaining questions

During the 2022 Winter Paralympic Games in Beijing, the Para snow-sport events will be held at high altitudes and in possibly cold conditions while also requiring adjustment to several time zones. Furthermore, the ongoing COVID-19 pandemic may lead to suboptimal preparations. Another concern is the high rate of injuries that have been reported in the Para alpine and snowboard events. In addition to these challenges, Para athletes various impairments may affect both sports-specific demands and athlete health. However, the group of Para snow-sport athletes is an understudied population. Accordingly, this perspective paper summarises current knowledge to consider when preparing for the Paralympic Games in Beijing and point out important unanswered questions. We here focus specifically on how sport-specific demands and impairment-related considerations are influenced by altitude acclimatisation, cold conditions, travel fatigue and jetlag, complications due to the COVID-19 pandemic, and injury prevention and sports safety considerations. As Para athletes with spinal cord injury, limb deficiency, cerebral palsy and visual impairment account for the majority of the Para snow-sport athletes, the focus is mainly on these impairment groups. In brief, we highlight the extra caution required to ensure athlete health, performance and sports safety among Para athletes participating in the snow-sport events in the 2022 Beijing Paralympic Games. Although there is an urgent need for more high-quality research focusing on Para winter athletes, we hope these non-consensus recommendations will help prepare for the 2022 Beijing Paralympic Winter Games.

Vocational situation and experiences from the work environment among individuals with neuromuscular diseases

BACKGROUND

Neuromuscular diseases (NMD) can affect the ability to be employed and to work, but there is limited knowledge of individuals' own perspectives of factors that are important for their vocational situation.

OBJECTIVE

To explore the vocational situation among people with NMD that are employed, and to describe their experiences of how their disability, personal and environmental factors influence their ability to continue to work.

METHODS

Nine participants with different NMD were included. A mixed-methods design was used, and data were collected by means of semi-structured and open-ended interviews, and ratings of aspects supporting or interfering with their work performance and the ability to continue to work. Data were analyzed with directed content analysis based on the International Classification of Functioning, Disability and Health, and with descriptive statistics.

RESULTS

The participants' personal characteristics, support from others at work and at home, and a flexible work organization were perceived as important factors facilitating work continuation, whereas physically demanding work assignments and factors in the physical environment were perceived as barriers.

CONCLUSIONS

Knowledge of how personal characteristics as well as support from the work organization, managers and family members can facilitate the ability to work is important for employers, staff within different parts of the health care system, and the social security system. Future research should focus on interventions that are best suited to enhance the vocational situation for individuals with NMD.

Leisure time physical activity among older adults with long-term spinal cord injury

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To describe participation in leisure time physical activity (LTPA) (amount, intensity and type) among older adults with long-term spinal cord injury (SCI), and to investigate the associations with sociodemographics, injury characteristics and secondary health conditions (SHCs).

SETTING

Home settings in southern Sweden.

METHODS

Data from the Swedish Aging with Spinal Cord Injury Study (SASCIS). The physical activity recall assessment for people with SCI was used to assess LTPA among 84 men and 35 women (mean age 63.5 years, mean time since injury 24 years, injury levels C1-L5, American Spinal Injury Association Impairment Scale A-D). Associations were analyzed statistically using hierarchical multivariable regression.

RESULTS

Twenty-nine percent reported no LTPA, whereas 53% performed moderate-to-heavy intensity LTPA. The mean minutes per day of total LTPA was 34.7 (±41.5, median 15, range 0-171.7) and of moderate-to-heavy LTPA 22.5 (±35.1, median 5.0, range 0-140.0). The most frequently performed activities were walking and wheeling. Sociodemographics, injury characteristics and SHCs (bowel-related and bladder-related problems, spasticity and pain) explained 10.6% and 13.4%, respectively, of the variance in total and moderate-to-heavy LTPA. Age and wheelchair use were significantly, negatively associated with total LTPA. Women, wheelchair users and employed participants performed significantly less moderate-to-heavy LTPA than men, those using walking devices/no mobility device and unemployed participants.

CONCLUSION

Many older adults with long-term SCI do not reach the amount or intensity of LTPA needed to achieve fitness benefits. Research is needed on how to increase LTPA and to identify modifiable factors that could enhance their participation.

Vocational outcome 6-15 years after a traumatic brain injury

PRIMARY OBJECTIVE

To describe vocational outcome 6-15 years after a traumatic brain injury (TBI) among individuals who were productive by working or studying at the time of their TBI and determine the associations with variables related to the time of injury and at follow-up.

METHODS AND PROCEDURES

Thirty-four individuals with a mild TBI and 45 with a moderate-to-severe TBI were assessed on average 10 years post-injury. Logistic regression was used to determine the association between their current vocational situation and variables related to the time of injury (gender, age, injury severity and educational level) and at follow-up (time since injury, marital status and overall disability).

RESULTS

A total of 67% were productive at follow-up. Age at injury, injury severity and the degree of disability at follow-up were strongly associated with being productive. Younger individuals with milder TBI and less severe disability were significantly more likely to be fully productive. No significant associations were found between productivity and gender, education, time since injury or marital status.

CONCLUSIONS

This study indicates that return to productivity in a long-term perspective after a TBI is possible, in particular when the individual is young, has sustained a mild TBI and has a milder form of overall disability.

Psychometric properties of the Satisfaction With Life Scale in Parkinson's disease

OBJECTIVE

The Satisfaction With Life Scale (SWLS) is a global measure of life satisfaction (LS). The objective of this study was to evaluate the psychometric properties (data completeness, scaling assumptions, targeting and reliability) of the SWLS in a sample of people with Parkinson's disease (PD).

MATERIALS AND METHODS

A postal survey including a Swedish version of the SWLS and demographic information was administered to 174 persons with PD; 97 responded and received a second survey after 2 weeks.

RESULTS

The mean (SD) age and PD duration of the 97 responders were 73 (8) and 7 (6) years, respectively. Data completeness was 92% to 97% for the five items in the SWLS and 92% for the total score (5-35 points). The mean score of the SWLS was 24.2 points (7.7), indicating that this group had an average LS. The items' means and SDs were roughly parallel and the score distribution was even. The internal consistency reliability (Cronbach's alpha) was 0.90. The test-retest reliability, assessed by the intraclass correlation coefficient, was 0.78. The scale showed no systematic difference between the first and second response. The standard error of measurement was 3.6 points, and the smallest detectable difference was 10.0 points.

CONCLUSIONS

This evaluation of the psychometric properties of the SWLS shows that the scale has good data completeness, scaling assumptions and targeting and that the internal consistency reliability and the test-retest reliability are acceptable. Thus, the SWLS is a psychometrically sound and suitable tool to asses LS in people with PD.

Sense of coherence and disability and the relationship with life satisfaction 6-15 years after traumatic brain injury in northern Sweden

The objective of the study was to assess sense of coherence (SOC) many years after traumatic brain injury (TBI) and explore the relationship between SOC and self-rated life satisfaction (LS) as well as measures of functioning and disability, sex, age at injury, injury severity and time post-injury. Sixty-six individuals (aged 18-65 years) who were 6-15 years post-injury were interviewed. Data on SOC (SOC-13 item scale), measures of functioning and disability (Mayo-Portland Adaptability Inventory, MPAI-4), LS (Satisfaction with Life Scale, SWLS), and sex, age at injury, injury severity and time post-injury were analysed with hierarchical multiple regression analyses. The results showed that SOC in the study group did not differ from the general population and was strongly associated with LS. Regression analyses revealed that emotional factors, social participation, SOC, and time since injury, were more influential than sex, age at injury, and injury severity in explaining LS. It was concluded that SOC in this group of individuals with TBI who were many years post-injury was similar to nondisabled individuals. SOC, together with emotional factors, social participation and injury-related factors, were determinants of LS. These results confirm that LS after TBI is a complex phenomenon dependent on several factors that are important targets for rehabilitation professionals.

Functioning and disability 6-15 years after traumatic brain injuries in northern Sweden

OBJECTIVES

To assess long-term functioning and disability after traumatic brain injury (TBI).

MATERIAL AND METHODS

Individuals (n = 88) in Norrbotten, northern Sweden, who had been transferred for neurosurgical care were assessed with internationally established TBI outcome measures 6-15 years post-injury.

RESULTS

There was an improvement in overall outcome from discharge from inpatient rehabilitation to follow-up. Many individuals had a high degree of motor and cognitive functioning, which enabled them to live independently in their own home without assistance, but there remained a disability related to community reintegration and social participation. This affected their productivity and to some degree their marital stability. The remaining disability and reduced productivity were related to the age at injury and the injury severity.

CONCLUSIONS

Our data showed that individuals with a TBI can achieve and maintain a high degree of functioning many years after the injury. Increasing age and a greater injury severity contributed to their long-term disability.

Muscle strength training, gait performance and physiotherapy after stroke

Hemiparesis after stroke, with muscle weakness and reduced gait performance, is a leading cause of long-term disability. To improve lower limb muscle strength and mobility post stroke, there is a need for effective training

METHODS

This review summarises the effects of lower limb progressive resistance training ([PRT]; loads of 70% or more of the maximum strength) on muscle strength, muscle tone, gait performance and perceived participation after stroke. PRT is a safe and effective way to improve muscle strength post stroke, without negative effects on muscle tone. Furthermore, improvements in muscle strength positively influence gait performance and perceived participation. Current recommendations for stroke rehabilitation include strength training, which can also be an effective form of fitness training for subjects with minor weakness. Despite its proven effectiveness, further studies are needed to find the most appropriate time to start PRT post-stroke, to identify those stroke individuals that can benefit most from PRT and how to combined PRT with other physiotherapeutic stroke interventions.

Effects of a goal-oriented rehabilitation program in mild cognitive impairment: a pilot study

BACKGROUND

Memory disturbance, deficient concentration, and fatigue are symptoms seen in amnestic mild cognitive impairment (MCI) as well as in mild traumatic brain injury (TBI). The aim of this study was to assess if an established rehabilitation program commonly used in TBI can aid MCI patients to develop compensatory memory strategies that can improve their cognition, occupational performance, and quality of life (QoL).

METHODS

Fifteen patients with MCI participated in the program 2 days per week for 8 weeks. Cognitive function, occupational performance, and self-perceived QoL were assessed at baseline, at the end of the intervention, and at follow-up after 6 months.

RESULTS

Significant improvements were seen in cognitive processing speed, occupational performance, and in some of the QoL domains.

CONCLUSION

As this goal-oriented rehabilitation program in MCI resulted in some improvements in cognition, occupational performance, and QoL, further randomized controlled studies are warranted.

Demographics, injury characteristics and outcome of traumatic brain injuries in northern Sweden

OBJECTIVES - To describe demographics, injury characteristics and outcome of traumatic brain injury (TBI) in northern Sweden over 10 years. MATERIAL AND METHODS - Data were retrospectively collected on those individuals (n = 332) in Norrbotten, northern Sweden, with a TBI who had been transferred for neurosurgical care from 1992 to 2001. RESULTS - A majority were older men with a mild TBI and an acute or chronic subdural hematoma following a fall. Younger individuals were fewer but had more often a severe TBI from a traffic accident. Most individuals received post-acute care and brain injury rehabilitation. A majority had a moderate or severe disability, but many were discharged back home with no major changes in their physical or social environment. CONCLUSIONS - Our data confirm the relationship between age, cause of injury, injury severity and outcome in relation to TBI and underscore the need for prevention as well as the importance of TBI as a cause of long-term disability.

Voluntary activation and central activation failure in the knee extensors in young women and men

Quadriceps muscle weakness is common after knee injuries. This weakness is caused, in part, by reduced voluntary activation (VA) because of central activation failure (CAF). Superimposed electrical stimulation techniques are used to assess VA and to detect CAF. The aim of this study was to assess VA during knee extension in young healthy women and men, and to evaluate subjective discomfort from the electrical stimulation. The quadriceps muscle in six young healthy women (mean age 22 years) and six young healthy men (mean age 29 years) was stimulated during maximal voluntary contractions using a 100 Hz pulse train. Data were collected from two test sessions separated by 6-8 days and each session comprised of two trials. A visual analog scale for pain (VAS-pain) was used to evaluate subjective discomfort. Overall, young healthy, moderately active men and women did have the ability to fully activate their knee extensors isometrically, but they did not achieve full activation on every trial. In those trials where a CAF was detected, the degree was small (mean less than 2%), and did not vary between the two test sessions. Subjective discomfort was generally moderate and tolerable (mean VAS-pain score 35 mm). These results will assist the clinical assessment of muscle weakness following a knee injury and facilitate the design and evaluation of appropriate rehabilitation interventions.

Diagnostic criteria and the use of ICD-10 codes to define and classify minor head injury

BACKGROUND

Epidemiological research on the incidence of traumatic head injuries relies on the correct definition and classification of the injury.

OBJECTIVE

To address the use of diagnostic criteria and ICD-10 codes to define minor head injury in Swedish hospitals managing patients with head injury.

METHODS

A questionnaire was mailed to all 76 Swedish hospitals managing head injuries. The hospitals were asked what diagnostic criteria they use to define minor head injury, and which ICD-10 codes they use to classify such injuries.

RESULTS

72 hospitals (95%) responded to the survey. The most common criterion was loss of consciousness (76%), followed by post-traumatic amnesia (38%). Almost half the hospitals used other signs and symptoms to define minor head injury. The ICD-10 code S.06 (intracranial injury) was used by 51 of the hospitals (91%).

CONCLUSIONS

It is essential that there should be common definitions, classifications, and registration of minor head injuries. The wide variation in definition and classification found in this study emphasises the importance of improved implementation of the present guidelines.

Enzyme activities in the tibialis anterior muscle of young moderately active men and women: relationship with body composition, muscle cross-sectional area and fibre type composition

The aims of this study were (i) to assess the differences between men and women in maximal activities of selected enzymes of aerobic and anaerobic pathways involved in skeletal muscle energy production, and (ii) to assess the relationships between maximal enzyme activities, body composition, muscle cross-sectional area (CSA) and fibre type composition. Muscle biopsies were obtained from the tibialis anterior (TA) muscle of 15 men and 15 women (age 20-31 years) with comparable physical activity levels. The muscle CSA was determined by magnetic resonance imaging (MRI). Maximal activities of lactate dehydrogenase (LDH), phosphofructokinase (PFK), beta-hydroxyacyl-coenzyme A dehydrogenase (HAD), succinate dehydrogenase (SDH) and citrate synthase (CS), were assayed spectrophotometrically. The proportion, mean area and relative area (proportion x area) of type 1 and type 2 fibres were determined from muscle biopsies prepared for enzyme histochemistry [myofibrillar adenosine triphosphatase (mATPase)]. The men were significantly taller (+6.6%; P < 0.001) and heavier (+19.1%; P < 0.001), had significantly larger muscle CSA (+19.0%; P < 0.001) and significantly larger areas and relative areas of both type 1 and type 2 fibres (+20.5-31.4%; P = 0.007 to P < 0.001). The men had significantly higher maximal enzyme activities than women for LDH (+27.6%; P = 0.007) and PFK (+25.5%; P = 0.003). There were no significant differences between the men and the women in the activities of HAD (+3.6%; ns), CS (+21.1%; P = 0.084) and SDH (+7.6%; ns). There were significant relationships between height and LDH (r = 0.41; P = 0.023), height and PFK (r = 0.41; P = 0.025), weight and LDH (r = 0.45; P = 0.013), and weight and PFK (r = 0.39; P = 0.032). The relationships were significant between the muscle CSA and the activities of LDH (r = 0.61; P < 0.001) and PFK (r = 0.56; P = 0.001), and between the relative area of type 2 fibres and the activities of LDH (r = 0.49; P = 0.006) and PFK (r = 0.42; P = 0.023). There were no significant relationships between HAD, CS and SDH, and height, weight, muscle CSA and fibre type composition, respectively. These data indicate that the higher maximal activities of LDH and PFK in men are related to the height, weight, muscle CSA and the relative area of type 2 fibres, which are all significantly larger in men than women.

Capillary supply of the tibialis anterior muscle in young, healthy, and moderately active men and women

Tibialis anterior muscle biopsies from moderately active men and women (21-30 yr; n = 30) were examined to determine potential gender differences in capillarization. The fiber type proportions [type I (T1) approximately 73%] were unaffected by gender. The men (M) had significantly (P < 0.001) larger fibers than the women (W), with a greater gender effect for type II (T2) fibers (P < 0.001). The M and W had similar capillary densities (CD approximately 390 capillaries/mm2), but the capillaries-to-fiber ratio (C/F) was higher in the M (M = 2.20 +/- 0.35, W = 1.66 +/- 0.32; P < 0.01). Capillary contacts (CC) were higher in T2 than T1 for the M (P < 0.01), but not W, and M had greater CC (P < 0.001). Both fiber area per capillary (FA/C) and fiber perimeter per capillary (FP/C) indicated that T1 fibers had greater capillarization than T2 fibers (P < 0.001). There were no gender differences in T1 FA/C and T2 FA/C or T1 FP/C, but a gender difference existed for T2 FP/C (M = 60.5 +/- 10.9, W = 70.6 +/- 13.4; P < 0.01). The gender difference for C/F could be explained by fiber size; however, the physiological implications of the difference in T2 FP/C remains to be determined. In conclusion, despite gender differences for fiber size, overall, capillarization was similar between the men and women.

Ankle dorsiflexor muscle performance in healthy young men and women: reliability of eccentric peak torque and work measurements

The aims of this study were: (i) to assess the test-retest intrarater reliability of eccentric ankle dorsiflexor muscle performance in young healthy men and women using the Biodex dynamometer; and (ii) to examine different statistical indices for the interpretation of reliability. Thirty men and women (age 22.5 +/- 2.5 years, mean +/- S.D.) performed three maximal eccentric contractions at 30 degrees/second and 90 degrees/second, with 7-10 days between test sessions. Reliability was evaluated with three intraclass correlation coefficients (ICC1,1, ICC2,1 and ICC3,1), and was excellent for peak torque (ICC 0.90-0.96) and good to excellent for work (ICC 0.69-0.83), with no discernible differences among the three ICCs. Method errors, assessed by the standard error of the measurement (S.E.M.) and S.E.M.%, were low. The Bland & Altman graphs and analyses indicated no significant systematic bias in the data. In conclusion, measurements of eccentric ankle dorsiflexor muscle performance in young healthy individuals using the Biodex are highly reliable.

[Sports and head injuries. Guidelines for the management and subsequent return to training and competition]

Head injuries in sports have received increased attention during the past decade. As explained in this article, the most recent guidelines for the management of head injuries in sports adopted by the American Academy of Neurology (AAN) have been adapted for the Swedish sports society. The guidelines include a grading scale of head injuries in sports, a sideline evaluation to aid physicians, coaches and athletes in the acute situation, and a management strategy for safe return to play after a head injury. The use of these guidelines will facilitate appropriate acute and subacute management and thereby prevent repeated head injuries that could lead to potentially catastrophic outcome or long-term cognitive sequelae.

Muscle structure and function in chronic neurological disorders: the potential of exercise to improve activities of daily living

Our knowledge of muscle function in chronic neurological disorders, the effects of exercise, and how the effects might translate into improvements in activities of daily living is very limited. By building a bridge between basic muscle physiology and clinical rehabilitation, our knowledge of the pathophysiological mechanisms underlying muscle dysfunction in people with chronic neurological disorders will increase. This will facilitate the design and subsequent evaluation of exercise programs for these people and improve our understanding of the effects of such interventions on performance of activities of daily living.

Reliability of isokinetic ankle dorsiflexor strength measurements in healthy young men and women

The purposes of this study were: (i) to determine the test-retest reliability of isokinetic ankle dorsiflexor strength measurements in young healthy adults using the Biodex dynamometer, and (ii) to examine several statistical measures for the interpretation of reliability. Thirty men and women (mean age 23 +/- 3 years) performed three maximal concentric contractions at 30 degrees/s, 60 degrees/s, 90 degrees/s, 120 degrees/s and 150 degrees/s. Reliability of peak torque, work and torque at a specific time were assessed by calculating the intraclass correlation coefficient (ICC 2,1), Pearson product moment correlation coefficient (r), standard error of the measurement (SEM), method error (ME) and coefficient of variation (CV), and by plotting the differences between observations against their means. Isokinetic tests of ankle dorsiflexor strength in healthy young adults using the Biodex dynamometer were highly reliable (ICC 0.61-0.93). It is recommended that test-retest reliability analyses include the ICC and assessments of measurement errors (SEM, ME or CV), as well as graphs to indicate any systematic variations in the data.

Superimposed single impulse and pulse train electrical stimulation: A quantitative assessment during submaximal isometric knee extension in young, healthy men

Superimposed electrical stimulation techniques can be used to detect central activation failure (CAF), defined as incomplete central nervous system recruitment, suboptimal activation of motor units, or both. The purpose of this study was to evaluate superimposed electrical stimulation techniques to be used to detect CAF during isometric knee extension. We performed three sets of experiments and compared the torque increments from transcutaneous electrical stimulation with: (i) single impulses of different amplitudes (100 V, 150 V, and 200 V) and a pulse train of 100 Hz (100 V, 100 ms); (ii) pulse trains (100 Hz, 100 V) of different lengths (100 ms, 200 ms, and 300 ms); and (iii) pulse trains (100 Hz, 100 ms) of different amplitudes (50 V, 100 V, 150 V, and 200 V). Stimulation was evaluated at submaximal (80% of MVC) isometric knee extension in 24 healthy young men using a Biodex isokinetic dynamometer. Electrodes were placed over the rectus femoris muscle and all stimulation impulses were monophasic, rectangular waves of 0.2-ms duration. Pulse train stimulation at 100 V always elicited a torque increment, whereas single impulse stimulation, even at 200 V, only caused a torque increment in about half of the trials. For each subject, the pulse train generated a significantly larger torque increment than for any of the three single impulses. There was no significant difference in torque increment between the three pulse trains of different lengths. Pulse trains at 150 V and 200 V generated significantly larger torque increments than at 50 V and 100 V. High-frequency maximal train stimulation may thus improve the detection of CAF during isometric knee extension. Detection of CAF may be important in the clinical assessment of muscle weakness, investigating the mechanisms underlying muscle weakness, and evaluating potential therapeutic strategies.

[Effects of strength and endurance training on skeletal muscles in the elderly. New muscles for old!]

A well-known effect of increasing age is the gradual reduction of muscle function, and thus of performance in the activity of daily living. Recent research has shown that, even among the very elderly, exercise can improve not only strength and endurance, but also balance and mobility, thus reducing the risk of falls. The possibility of counteracting some of the age-related muscle changes has also been demonstrated. The article reviews current knowledge of strength and endurance training in the elderly, the importance of exercise to improve physical performance, and how lifelong exercise can counteract the effects associated with the ageing of the neuromuscular system.

Effects of contraction duration on low-frequency fatigue in voluntary and electrically induced exercise of quadriceps muscle in humans

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.

Evidence for nervous system degeneration with advancing age

Human skeletal muscle undergoes major structural and functional changes with advancing age. A progressive degeneration of the nervous system is now considered a major factor underlying these alterations. This review will briefly describe the changes that occur in the human motor unit with increasing age and focus specifically on the changes that relate to a degeneration of the nervous system.

Skeletal muscle fatigue and endurance in young and old men and women

The effects of increasing age on skeletal muscle fatigue and endurance were assessed in 22 healthy young (14 men and 8 women; mean age, 28 +/- 6 years) and 16 healthy old (8 men and 8 women; mean age, 73 +/- 3 years) individuals. All subjects performed 100 repeated maximum dynamic knee extensions at 90 degrees.s-1 (1.57 rad.s-1) using an isokinetic dynamometer (Cybex II). Peak torque was recorded during every contraction, and for each individual the maximal voluntary contraction (MVC), the fatigue rate, the endurance level, and the relative reduction in muscle force were determined. MVC and endurance level were significantly lower in old men and women, but there was no discernible difference in relative muscle force reduction and fatigue rate between young and old individuals. We conclude that thigh muscles of older individuals are weaker than those of younger individuals, but relative to their strength, older individuals have similar properties as younger individuals with respect to muscle fatigue and endurance.

Heavy-resistance training in older Scandinavian men and women: short- and long-term effects on arm and leg muscles

The short- and long-term effects of heavy-resistance training (85% of one-repetition maximum (RM)) on elbow flexion and knee extension dynamic and isokinetic strength and on morphology in the biceps brachii and vastus lateralis muscles were evaluated during 1 year in 35 Scandinavian men and women, aged 70-77 years, 12 of whom formed a control group. After the first 11 weeks of training (n = 23; 3 times/week) elbow flexion and knee extension dynamic strength (1 RM) had increased [mean +/- SD] 49% +/- 16 and 163% +/- 75, respectively, with no significant difference between men and women. For the following 27 weeks, strength was maintained with one training session per week (n = 12) but dropped without training (n = 11). After the final 11 weeks of training (n = 11; 3 times/week), strength had further increased 32% +/- 16 in both the arm and the leg. Isokinetic strength measurements (Cybex II; 30 degrees/s) revealed similar but smaller gains than for dynamic strength. Muscle biopsies (n = 20) taken at the start and after the first 11 weeks of training showed a significant increase in the area of both type 1 and type 2 fibers in the biceps brachii muscle and a positive significant correlation between the percentage increase in the proportional area of type 2 fibers in the vastus lateralis muscle and the percentage increase in knee extension dynamic muscle strength. In conclusion, older Scandinavian men and women have a high capacity both to improve and to maintain muscle strength, some of which is mediated through an adaptation in the muscle fiber type population.

Human aging, muscle mass, and fiber type composition

To assess the age-related loss of muscle mass and to determine the mechanisms behind this aging atrophy, the muscle structure and fiber type composition have been estimated, using invasive and noninvasive techniques. Limb muscles from older men and women are 25-35% smaller and have significantly more fat and connective tissue than limb muscles from younger individuals. Comparisons of muscle biopsies from younger and older individuals reveal that type 2 (fast-twitch) fibers are smaller in the old, while the size of type 1 (slow-twitch) fibers is much less affected. Studies of whole muscle cross sections also show a significantly smaller number of muscle fibers, a significantly lower relative type 2 fiber area, and a significant increase in fiber type grouping with increasing age. These results indicate a gradual decrease in size/volume with advancing age, accompanied by a replacement by fat and connective tissue. This aging atrophy seems to be due to a reduction in both number and size of muscle fibers, mainly of type 2, and is to some extent caused by a slowly progressive neurogenic process.

Aging of human muscle: structure, function and adaptability

With increasing age, human skeletal muscles gradually decrease in volume, mainly due to a reduced number of motor units and muscle fibers, and a reduced size of type 2 fibers. As a result, progressive weakening and impaired mobility occur. High-resistance strength training is beneficial, even in the very old, and could possibly reverse some of the detrimental effects of age-related weakness. The importance of exercise for older people affords an excellent opportunity for the medicine community as a major source of information and promotion of physical activity for this rapidly growing segment of the population. In this review, we summarize the current knowledge of the effects of aging on the human neuromuscular system, describe some of the major underlying mechanisms of the aging atrophy and focus on the importance of strength training to improve muscle function in older people.

Submaximal-exercise-induced impairment of human muscle to develop and maintain force at low frequencies of electrical stimulation

The aim of this study was to test the hypothesis that low intensity exercise-induced low frequency fatigue is caused by failure of excitation-contraction coupling. Changes in knee extension torque at 5, 10, 15, 20 and 50 Hz electrical stimulation of quadriceps muscle in ten healthy, young, male subjects were recorded during 20-min voluntary exercise followed by 60-min recovery. In seven of the ten subjects, changes in torque during 3 min of 10-Hz stimulation were recorded 2 min and 20 min after 20 min voluntary exercise. Exercise was performed at 30% of maximal voluntary contraction with a contraction plus relaxation period of 6 plus 4 s. Torque at 5, 10, 15, 20 and 50-Hz stimulation at the end of exercise was reduced to mean 91.0 (SEM 5.4)%, 68.7 (SEM 5.4)%, 67.2 (SEM 3.9)%, 66.5 (SEM 4.5)% and 74.7 (SEM 4.3)% of control values, respectively. During the first 30 s of the 3 min 10-Hz stimulation, torque was reduced in exercised muscle and increased in nonfatigued muscle. The reduction in torque was more marked 20 min after exercise than after 2 min. In conclusion, the pattern of depression and recovery of muscle force observed was in agreement with the hypothesis that the main cause of low intensity exercise-induced low frequency fatigue is an impairment of excitation-contraction coupling.

Fibre type composition of rabbit tibialis anterior and extensor digitorum longus muscles

Rabbit tibialis anterior (TA) and extensor digitorum longus (EDL) muscles are used extensively in studies of stimulation-induced fibre type transformation, but the proportions and sizes of the 2 main fibre types, and the way in which they are distributed within the muscles, have never been described in any detail. In this study, transverse sections were processed by enzyme histochemical and immunohistochemical techniques and assessed morphometrically. The data were analysed by multivariate methods. In both TA and EDL muscles, the proportion of type 1 fibres varied significantly, and to a similar extent, within a cross-section, from lateral to medial and from superficial to deep parts. The fibre density, an indirect estimate of the mean muscle fibre area, also varied significantly, but not systematically, within a cross-section. For the EDL muscle, the proportion of type 1 fibres was consistently higher in the distal than in the proximal part of the muscle. The proportion of type 1 fibres was also significantly higher in the EDL than in the TA muscle for each of the 6 rabbits. There was no systematic variation between muscles from left and right limbs. The type proportions and fibre densities for both TA and EDL muscles differed significantly between individual rabbits, but not between sexes. The study provides a database that has hitherto been lacking on normal fibre type composition and its variation within and between these experimentally important muscles.

Stimulation-induced damage in rabbit fast-twitch skeletal muscles: a quantitative morphological study of the influence of pattern and frequency

The aim of this study was to determine whether muscle fibre degeneration brought about by chronic low-frequency electrical stimulation was related to the pattern and frequency of stimulation. Rabbit fast-twitch muscles, tibialis anterior and extensor digitorum longus, were stimulated for 9 days with pulse trains ranging in frequency from 1.25 Hz to 10 Hz. Histological data from these muscles were analysed with multivariate statistical techniques. At the lower stimulation frequencies there was a significantly lower incidence of degenerating muscle fibres. Fibres that reacted positively with an antineonatal antibody were most numerous in the sections that revealed the most degeneration. The dependence on frequency was generally similar for the two muscles, but the extensor digitorum longus muscles showed more degeneration than the tibialis anterior at every frequency. Muscles subjected to 10 Hz intermittent stimulation showed significantly less degeneration than muscles stimulated with 5 Hz continuously, although the aggregate number of impulses delivered was the same. The incidence of degeneration in the extensor digitorum longus muscles stimulated at 1.25 Hz was indistinguishable from that in control, unstimulated muscles; for the tibialis anterior muscles, this was also true for stimulation at 2.5 Hz. We conclude that damage is not an inevitable consequence of electrical stimulation. The influence of pattern and frequency on damage should be taken into account when devising neuromuscular stimulation regimes for clinical use.