European children and adolescents spend most of their daily life and especially their school hour... more European children and adolescents spend most of their daily life and especially their school hours being sedentary which may increase their risk for chronic non-communicable diseases later in life. After the curriculum reform of Finnish basic education in 2014, most of the new or renovated comprehensive schools in Finland incorporate open and flexible classroom designs. Their open learning spaces may provide students opportunities to reduce sedentary behavior during school hours. Thus, waist-worn accelerometers were used to assess classroom-based sedentary time (ST), the number of breaks from sedentary time (BST), and physical activity (PA) among cross-sectional samples of 3rd and 5th grade students during two separate academic years in a school that underwent a renovation from conventional classrooms to open learning spaces. The cohort of 5th grade students before renovation had a smaller proportion of ST from total classroom time (56.97 ± 12.24%, n = 42 vs. 67.68 ± 5.61%, n = 28, ...
Purpose Numerous exercise interventions to enhance motor function in cerebral palsy (CP) have bee... more Purpose Numerous exercise interventions to enhance motor function in cerebral palsy (CP) have been proposed, with varying degrees of effectiveness. Since motor function requires a combination of muscle strength, joint flexibility and motor coordination, we designed a supervised multicomponent exercise intervention (EXECP) for individuals with CP. Our aim was to evaluate the effects of the EXECP intervention and its retention after it ceased. Methods The EXECP intervention combined strength training for the lower limbs and trunk muscles, passive stretching for the lower limb muscles and inclined treadmill gait training. Eighteen participants with CP (mean age: 14, 13 males) were tested twice before the three-month intervention and twice after the intervention, each test separated by three months. Seventeen typically developing age and sex-matched controls were tested twice. Motor function was assessed with the six minutes walking test (6MWT) and the gross motor function measure (GMFM...
Hyper-resistance is an increased resistance to passive muscle stretch, a common feature in neurol... more Hyper-resistance is an increased resistance to passive muscle stretch, a common feature in neurological disorders. Stretch hyperreflexia, an exaggerated stretch reflex response, is the neural velocity-dependent component of hyper-resistance, and has been quantitatively measured using the stretch reflex threshold (i.e., joint angle at the stretch reflex electromyographic onset). In this study, we introduce a correction in how the stretch reflex threshold is calculated, by accounting for the stretch reflex latency (i.e., time between the stretch reflex onset at the muscle spindles and its appearance in the electromyographic signal). Furthermore, we evaluated how this correction affects the stretch reflex threshold in children and young adults with spastic cerebral palsy. A motor-driven ankle dynamometer induced passive ankle dorsiflexions at four incremental velocities in 13 children with cerebral palsy (mean age: 13.5 years, eight males). The stretch reflex threshold for soleus and m...
This study aimed to examine whether fixing the ankle in dorsiflexion vs in plantarflexion affects... more This study aimed to examine whether fixing the ankle in dorsiflexion vs in plantarflexion affects knee flexion torque and hamstrings activity during ramp isometric contractions. Ten pairs of fine wires were inserted into the four heads of the hamstrings and 15-channel high-density electromyography (EMG) arrays were attached over the biceps femoris long head (BFLH) and semitendinosus (ST) muscles of the right leg of 12 young males. Results suggest that higher hamstrings EMG activity is reached in BFLH, ST and BF short head when the ankle is plantar flexed vs dorsiflexed at 20° knee flexion (but not at 90° knee flexion). This suggests that plantar flexion should be applied when prescribing hamstring exercises requiring a near-extended knee.
INTRODUCTION:Ankle plantar flexors substantially contribute to propulsion in human walking, and t... more INTRODUCTION:Ankle plantar flexors substantially contribute to propulsion in human walking, and their relative contributions may be affected by the type of footwear used. In this study, we aimed to ...
Majority of children are unable to meet the recommended 60 minutes of daily moderate to vigorous ... more Majority of children are unable to meet the recommended 60 minutes of daily moderate to vigorous physical activity (MVPA). Even participation into organized sport may not guarantee that recommended amount of activity is reached. Purpose of this study was to examine the amount and intensity of physical activity (PA) on days with and without practices and to find out whether daytime PA preceding soccer practice is associated with certain practice-time PA intensity level. Daily light, moderate and vigorous PA of 18 boys between 12 to 13 years of age engaged in soccer was measured for 9 days with and without soccer practices with wrist-worn Polar A300 activity meter. In addition, PA during practices was extracted and compared to PA preceding the practice session. The daily MVPA was twice as high on days with training as compared to days without training both on weekdays (mean difference ± 95% confidence interval = 67 min ± 14 min) and on weekend (63 min ± 36 min). PA preceding soccer practice had a positive correlation with all PA intensity levels during practice (r = 0.34-0.84, p<0.05-0.01). Physical activity should be promoted especially on days without organized practices and children should be encouraged to be physically active throughout the day as this was not found to compromise their activity during training.
Purpose Measurement of medial gastrocnemius (MG) tendon length using ultrasonography (US) require... more Purpose Measurement of medial gastrocnemius (MG) tendon length using ultrasonography (US) requires the muscle–tendon junction (MTJ) to be located. Previously, the MG MTJ has been tracked from different proximo-distal locations near the MTJ, which could influence estimates of tendon length change due to the different characteristics of the aponeurosis and tendon. We used US to evaluate the effect of tracking point location on MG MTJ displacement during maximal and submaximal (10, 20 and 30% of the non-injured maximal) isometric plantar flexion contractions. Methods Displacement behaviour of MTJ was tracked from (1) the exact MTJ; and (2) from an insertion point of a muscle fascicle on the aponeurosis 1.3 ± 0.6 cm proximal to the MTJ, in both limbs of patients with unilateral Achilles tendon rupture (ATR) (n = 22, 4 females, 42 ± 9 years, 177 ± 9 cm, 79 ± 10 kg). Results In the non-injured limb, displacement (1.3 ± 0.5 cm vs. 1.1 ± 0.6 cm) and strain (6.7 ± 2.8% vs. 5.8 ± 3.3%) during...
We investigated the ability of energy expenditure, movement sensing, and muscle activity to discr... more We investigated the ability of energy expenditure, movement sensing, and muscle activity to discriminate sedentary and non-sedentary activities in children. Thirty-five 7-11-year-old children participated in the study. Simultaneous assessment of oxygen uptake (VȮ 2), triaxial accelerometry, and thigh muscle electromyography (EMG) were performed during eight different sedentary and non-sedentary activities including lying down, sitting-, standing-, and walking-related activities, which were performed in a random order. Mean values of VȮ 2 , accelerometry, and EMG from the concurrent 2 min epochs during each activity were computed. Resting energy expenditure (REE) was measured during 30 min supine rest. Directly measured metabolic equivalent of tasks (METs, VȮ 2 in activities/VȮ 2 in REE) were calculated for each activity. Mean amplitude deviation (MAD) was computed for accelerometry. EMG was normalized for mean muscle activity during self-paced walking. The classification accuracy of METs, MAD, and EMG to discriminate sedentary activities from physical activities was investigated by receiver operating characteristic curves and optimal cutoffs based on maximal sensitivity and specificity. Mean (SD) REE was 5.0 ± 0.8 ml/kg/min. MET, MAD, and EMG values ranged from 1.0 to 4.9, 0.0020 to 0.4146 g, and 4.3 to 133.9% during lying down and walking at 6 km/h, respectively. Optimal cutoffs to discriminate sedentary activities from non-sedentary activities were 1.3 for METs (sensitivity = 82%, specificity = 88%), 0.0033 g for MAD (sensitivity = 80%, specificity = 91%), and 11.9% for EMG (sensitivity = 79%, specificity = 92%). In conclusion, this study provides applicable thresholds to differentiate sitting and standing and sedentary and non-sedentary activities based on METs, MAD, and EMG in young children.
Instead of TD, volume of high-intensity running appears to better reflect the requirements of the... more Instead of TD, volume of high-intensity running appears to better reflect the requirements of the game [7, 15-17] as elite athletes tend to cover larger distances at high intensities than domestic athletes [2]. Regrettably, there is inconsistency in women's football research concerning speed zones and their definitions [1]. High-speed running (16-20 km/h) and sprinting (> 20 km/h) zones have been used in the previous literature [8, 12, 18-20]. Recent studies [10, 11] however, have used thresholds including 12.5 km/h for high-speed running (HSR), 19.0 km/h for very high-speed running (VHSR), and 22.5 km/h for sprinting (SPR) as suggested by Park et al. [21]. A match analysis of the FIFA Women's World Cup 2019 used almost identical thresholds for the highest three zones: 13 km/h (Zone 3), 19 km/h (Zone 4), and 23 km/h (Zone 5) [1]. Elite level female players have been shown to complete from 1676-2749 m of HSR, 349-666 m of VHSR and 82-255 m of SPR depending on the playing position [1, 11]. The volume of high-intensity running has been shown to vary considerably between different positions [1, 8, 9, 12, 22]. CD cover the lowest distances in high-intensity zones [1, 11, 12, 22] whereas Original Paper
International Journal of Environmental Research and Public Health, 2020
Accelerometer-derived estimates of physical activity (PA) and sedentary time have been an importa... more Accelerometer-derived estimates of physical activity (PA) and sedentary time have been an important methodological focus. However, little is known about the daily activities among older people during their normal lives. Furthermore, some older individuals would like to be more active, yet experience an unmet PA need, which is defined as the desire to engage in more PA but without the opportunity to act on the desire. This study examined the intensity of daily PA and sedentary behavior measured with accelerometers among older people, and whether PA differs between weekdays and weekends and those with and without the experience of unmet PA need, measured with self-reports. A total of 174 community-dwelling older people (64% female) aged 75 to 90 years used an accelerometer for 7 consecutive days during waking hours, and the results were classified for sedentary behavior (thresholds of 0.0167 g), light activity (0.091 g), and moderate-to-vigorous activity (MVPA, 0.414 g) based on mean ...
Background To investigate whether physical performance is independently of physical activity (PA)... more Background To investigate whether physical performance is independently of physical activity (PA) associated with positive and negative dimensions of mental well-being in middle-aged women. Methods Data were drawn from the Estrogenic Regulation of Muscle Apoptosis (ERMA) study in which women 47 to 55 years were randomly selected from the Finnish National Registry. They (n = 909) participated in measurements of physical performance (handgrip force, knee extension force, vertical jumping height, maximal walking speed, and six-minute walking distance). Both mental well-being (the Centre for Epidemiologic Studies Depression Scale, the International Positive and Negative Affect Schedule Short Form and the Satisfaction with Life Scale) and PA were self-reported. Associations between variables were analysed using multivariate linear regression modelling adjusted for body height, fat mass %, menopausal status and symptoms, marital status, parity, employment status, self-reported mental diso...
International Journal of Environmental Research and Public Health, 2020
Limited data are available regarding strength and endurance training adaptations to occupational ... more Limited data are available regarding strength and endurance training adaptations to occupational physical performance during deployment. This study assessed acute training-induced changes in neuromuscular (electromyography; EMG) and metabolic (blood lactate, BLa) responses during a high-intensity military simulation test (MST), performed in the beginning (PRE) and at the end (POST) of a six-month crisis-management operation. MST time shortened (145 ± 21 vs. 129 ± 16 s, −10 ± 7%, p < 0.001) during the operation. Normalized muscle activity increased from PRE to POST in the hamstring muscles by 87 ± 146% (116 ± 52 vs. 195 ± 139%EMGMVC, p < 0.001) and in the quadriceps by 54 ± 81% (26 ± 8 vs. 40 ± 20%EMGMVC, p < 0.001). In addition, higher acute BLa values were measured after MST during POST. Changes in BLa and EMG suggested an increased neural input and metabolic rate during POST MST, likely leading to faster performance times at the end of the operation. High EMG values throu...
Background The majority of hamstring strain injuries (HSIs) occur in the late swing phase of high... more Background The majority of hamstring strain injuries (HSIs) occur in the late swing phase of high-speed running when hamstrings work eccentrically. The proximal region of the biceps femoris (BF) seems to be the most common site of injury. Elongation of the fascicles in eccentric contractions is higher in the proximal region compared to the distal region of BF, but the neural background to this phenomenon is not clear. Objective To examine the region-specificity of BF muscle activity at different running speeds. Design Observational study. Running speeds were randomized. Setting Laboratory, amateur level. Participants Football players without acute injury/illness, and without HSI history were recruited. Data collection is ongoing; six players have been measured and analysed so far. Assessment After warm-up, players ran on a treadmill at 12, 15, 18 km/h, and maximum speed. Electromyographic activity (EMG) along the BF and joint angular displacements were recorded with a 16-channel high-density EMG array and 3-D motion analysis, respectively. EMG data were normalized to maximal voluntary isometric contraction. Main Outcome Measures Normalized root-mean-square activity was calculated in the proximal, middle and distal muscle regions, and BF elongation was calculated using musculoskeletal modelling. Results Higher BF elongation and activity were observed in all regions with increasing speed. Activity in the proximal region was lower compared to the distal region at 15, 18 km/h and maximum speed, by 12, 18, and 35%, respectively. Conclusions Lower relative activity in the proximal region and greater proximal-distal differences in activity with increasing speed may indicate why HSIs occur at higher speeds, and mainly in the proximal region. Lower proximal activity may be associated with the higher elongation in this region during eccentric contractions that has been reported previously. Future studies are needed to examine whether players with higher within-muscle heterogeneity in muscle recruitment are at higher risk for HSI.
European children and adolescents spend most of their daily life and especially their school hour... more European children and adolescents spend most of their daily life and especially their school hours being sedentary which may increase their risk for chronic non-communicable diseases later in life. After the curriculum reform of Finnish basic education in 2014, most of the new or renovated comprehensive schools in Finland incorporate open and flexible classroom designs. Their open learning spaces may provide students opportunities to reduce sedentary behavior during school hours. Thus, waist-worn accelerometers were used to assess classroom-based sedentary time (ST), the number of breaks from sedentary time (BST), and physical activity (PA) among cross-sectional samples of 3rd and 5th grade students during two separate academic years in a school that underwent a renovation from conventional classrooms to open learning spaces. The cohort of 5th grade students before renovation had a smaller proportion of ST from total classroom time (56.97 ± 12.24%, n = 42 vs. 67.68 ± 5.61%, n = 28, ...
Purpose Numerous exercise interventions to enhance motor function in cerebral palsy (CP) have bee... more Purpose Numerous exercise interventions to enhance motor function in cerebral palsy (CP) have been proposed, with varying degrees of effectiveness. Since motor function requires a combination of muscle strength, joint flexibility and motor coordination, we designed a supervised multicomponent exercise intervention (EXECP) for individuals with CP. Our aim was to evaluate the effects of the EXECP intervention and its retention after it ceased. Methods The EXECP intervention combined strength training for the lower limbs and trunk muscles, passive stretching for the lower limb muscles and inclined treadmill gait training. Eighteen participants with CP (mean age: 14, 13 males) were tested twice before the three-month intervention and twice after the intervention, each test separated by three months. Seventeen typically developing age and sex-matched controls were tested twice. Motor function was assessed with the six minutes walking test (6MWT) and the gross motor function measure (GMFM...
Hyper-resistance is an increased resistance to passive muscle stretch, a common feature in neurol... more Hyper-resistance is an increased resistance to passive muscle stretch, a common feature in neurological disorders. Stretch hyperreflexia, an exaggerated stretch reflex response, is the neural velocity-dependent component of hyper-resistance, and has been quantitatively measured using the stretch reflex threshold (i.e., joint angle at the stretch reflex electromyographic onset). In this study, we introduce a correction in how the stretch reflex threshold is calculated, by accounting for the stretch reflex latency (i.e., time between the stretch reflex onset at the muscle spindles and its appearance in the electromyographic signal). Furthermore, we evaluated how this correction affects the stretch reflex threshold in children and young adults with spastic cerebral palsy. A motor-driven ankle dynamometer induced passive ankle dorsiflexions at four incremental velocities in 13 children with cerebral palsy (mean age: 13.5 years, eight males). The stretch reflex threshold for soleus and m...
This study aimed to examine whether fixing the ankle in dorsiflexion vs in plantarflexion affects... more This study aimed to examine whether fixing the ankle in dorsiflexion vs in plantarflexion affects knee flexion torque and hamstrings activity during ramp isometric contractions. Ten pairs of fine wires were inserted into the four heads of the hamstrings and 15-channel high-density electromyography (EMG) arrays were attached over the biceps femoris long head (BFLH) and semitendinosus (ST) muscles of the right leg of 12 young males. Results suggest that higher hamstrings EMG activity is reached in BFLH, ST and BF short head when the ankle is plantar flexed vs dorsiflexed at 20° knee flexion (but not at 90° knee flexion). This suggests that plantar flexion should be applied when prescribing hamstring exercises requiring a near-extended knee.
INTRODUCTION:Ankle plantar flexors substantially contribute to propulsion in human walking, and t... more INTRODUCTION:Ankle plantar flexors substantially contribute to propulsion in human walking, and their relative contributions may be affected by the type of footwear used. In this study, we aimed to ...
Majority of children are unable to meet the recommended 60 minutes of daily moderate to vigorous ... more Majority of children are unable to meet the recommended 60 minutes of daily moderate to vigorous physical activity (MVPA). Even participation into organized sport may not guarantee that recommended amount of activity is reached. Purpose of this study was to examine the amount and intensity of physical activity (PA) on days with and without practices and to find out whether daytime PA preceding soccer practice is associated with certain practice-time PA intensity level. Daily light, moderate and vigorous PA of 18 boys between 12 to 13 years of age engaged in soccer was measured for 9 days with and without soccer practices with wrist-worn Polar A300 activity meter. In addition, PA during practices was extracted and compared to PA preceding the practice session. The daily MVPA was twice as high on days with training as compared to days without training both on weekdays (mean difference ± 95% confidence interval = 67 min ± 14 min) and on weekend (63 min ± 36 min). PA preceding soccer practice had a positive correlation with all PA intensity levels during practice (r = 0.34-0.84, p<0.05-0.01). Physical activity should be promoted especially on days without organized practices and children should be encouraged to be physically active throughout the day as this was not found to compromise their activity during training.
Purpose Measurement of medial gastrocnemius (MG) tendon length using ultrasonography (US) require... more Purpose Measurement of medial gastrocnemius (MG) tendon length using ultrasonography (US) requires the muscle–tendon junction (MTJ) to be located. Previously, the MG MTJ has been tracked from different proximo-distal locations near the MTJ, which could influence estimates of tendon length change due to the different characteristics of the aponeurosis and tendon. We used US to evaluate the effect of tracking point location on MG MTJ displacement during maximal and submaximal (10, 20 and 30% of the non-injured maximal) isometric plantar flexion contractions. Methods Displacement behaviour of MTJ was tracked from (1) the exact MTJ; and (2) from an insertion point of a muscle fascicle on the aponeurosis 1.3 ± 0.6 cm proximal to the MTJ, in both limbs of patients with unilateral Achilles tendon rupture (ATR) (n = 22, 4 females, 42 ± 9 years, 177 ± 9 cm, 79 ± 10 kg). Results In the non-injured limb, displacement (1.3 ± 0.5 cm vs. 1.1 ± 0.6 cm) and strain (6.7 ± 2.8% vs. 5.8 ± 3.3%) during...
We investigated the ability of energy expenditure, movement sensing, and muscle activity to discr... more We investigated the ability of energy expenditure, movement sensing, and muscle activity to discriminate sedentary and non-sedentary activities in children. Thirty-five 7-11-year-old children participated in the study. Simultaneous assessment of oxygen uptake (VȮ 2), triaxial accelerometry, and thigh muscle electromyography (EMG) were performed during eight different sedentary and non-sedentary activities including lying down, sitting-, standing-, and walking-related activities, which were performed in a random order. Mean values of VȮ 2 , accelerometry, and EMG from the concurrent 2 min epochs during each activity were computed. Resting energy expenditure (REE) was measured during 30 min supine rest. Directly measured metabolic equivalent of tasks (METs, VȮ 2 in activities/VȮ 2 in REE) were calculated for each activity. Mean amplitude deviation (MAD) was computed for accelerometry. EMG was normalized for mean muscle activity during self-paced walking. The classification accuracy of METs, MAD, and EMG to discriminate sedentary activities from physical activities was investigated by receiver operating characteristic curves and optimal cutoffs based on maximal sensitivity and specificity. Mean (SD) REE was 5.0 ± 0.8 ml/kg/min. MET, MAD, and EMG values ranged from 1.0 to 4.9, 0.0020 to 0.4146 g, and 4.3 to 133.9% during lying down and walking at 6 km/h, respectively. Optimal cutoffs to discriminate sedentary activities from non-sedentary activities were 1.3 for METs (sensitivity = 82%, specificity = 88%), 0.0033 g for MAD (sensitivity = 80%, specificity = 91%), and 11.9% for EMG (sensitivity = 79%, specificity = 92%). In conclusion, this study provides applicable thresholds to differentiate sitting and standing and sedentary and non-sedentary activities based on METs, MAD, and EMG in young children.
Instead of TD, volume of high-intensity running appears to better reflect the requirements of the... more Instead of TD, volume of high-intensity running appears to better reflect the requirements of the game [7, 15-17] as elite athletes tend to cover larger distances at high intensities than domestic athletes [2]. Regrettably, there is inconsistency in women's football research concerning speed zones and their definitions [1]. High-speed running (16-20 km/h) and sprinting (> 20 km/h) zones have been used in the previous literature [8, 12, 18-20]. Recent studies [10, 11] however, have used thresholds including 12.5 km/h for high-speed running (HSR), 19.0 km/h for very high-speed running (VHSR), and 22.5 km/h for sprinting (SPR) as suggested by Park et al. [21]. A match analysis of the FIFA Women's World Cup 2019 used almost identical thresholds for the highest three zones: 13 km/h (Zone 3), 19 km/h (Zone 4), and 23 km/h (Zone 5) [1]. Elite level female players have been shown to complete from 1676-2749 m of HSR, 349-666 m of VHSR and 82-255 m of SPR depending on the playing position [1, 11]. The volume of high-intensity running has been shown to vary considerably between different positions [1, 8, 9, 12, 22]. CD cover the lowest distances in high-intensity zones [1, 11, 12, 22] whereas Original Paper
International Journal of Environmental Research and Public Health, 2020
Accelerometer-derived estimates of physical activity (PA) and sedentary time have been an importa... more Accelerometer-derived estimates of physical activity (PA) and sedentary time have been an important methodological focus. However, little is known about the daily activities among older people during their normal lives. Furthermore, some older individuals would like to be more active, yet experience an unmet PA need, which is defined as the desire to engage in more PA but without the opportunity to act on the desire. This study examined the intensity of daily PA and sedentary behavior measured with accelerometers among older people, and whether PA differs between weekdays and weekends and those with and without the experience of unmet PA need, measured with self-reports. A total of 174 community-dwelling older people (64% female) aged 75 to 90 years used an accelerometer for 7 consecutive days during waking hours, and the results were classified for sedentary behavior (thresholds of 0.0167 g), light activity (0.091 g), and moderate-to-vigorous activity (MVPA, 0.414 g) based on mean ...
Background To investigate whether physical performance is independently of physical activity (PA)... more Background To investigate whether physical performance is independently of physical activity (PA) associated with positive and negative dimensions of mental well-being in middle-aged women. Methods Data were drawn from the Estrogenic Regulation of Muscle Apoptosis (ERMA) study in which women 47 to 55 years were randomly selected from the Finnish National Registry. They (n = 909) participated in measurements of physical performance (handgrip force, knee extension force, vertical jumping height, maximal walking speed, and six-minute walking distance). Both mental well-being (the Centre for Epidemiologic Studies Depression Scale, the International Positive and Negative Affect Schedule Short Form and the Satisfaction with Life Scale) and PA were self-reported. Associations between variables were analysed using multivariate linear regression modelling adjusted for body height, fat mass %, menopausal status and symptoms, marital status, parity, employment status, self-reported mental diso...
International Journal of Environmental Research and Public Health, 2020
Limited data are available regarding strength and endurance training adaptations to occupational ... more Limited data are available regarding strength and endurance training adaptations to occupational physical performance during deployment. This study assessed acute training-induced changes in neuromuscular (electromyography; EMG) and metabolic (blood lactate, BLa) responses during a high-intensity military simulation test (MST), performed in the beginning (PRE) and at the end (POST) of a six-month crisis-management operation. MST time shortened (145 ± 21 vs. 129 ± 16 s, −10 ± 7%, p < 0.001) during the operation. Normalized muscle activity increased from PRE to POST in the hamstring muscles by 87 ± 146% (116 ± 52 vs. 195 ± 139%EMGMVC, p < 0.001) and in the quadriceps by 54 ± 81% (26 ± 8 vs. 40 ± 20%EMGMVC, p < 0.001). In addition, higher acute BLa values were measured after MST during POST. Changes in BLa and EMG suggested an increased neural input and metabolic rate during POST MST, likely leading to faster performance times at the end of the operation. High EMG values throu...
Background The majority of hamstring strain injuries (HSIs) occur in the late swing phase of high... more Background The majority of hamstring strain injuries (HSIs) occur in the late swing phase of high-speed running when hamstrings work eccentrically. The proximal region of the biceps femoris (BF) seems to be the most common site of injury. Elongation of the fascicles in eccentric contractions is higher in the proximal region compared to the distal region of BF, but the neural background to this phenomenon is not clear. Objective To examine the region-specificity of BF muscle activity at different running speeds. Design Observational study. Running speeds were randomized. Setting Laboratory, amateur level. Participants Football players without acute injury/illness, and without HSI history were recruited. Data collection is ongoing; six players have been measured and analysed so far. Assessment After warm-up, players ran on a treadmill at 12, 15, 18 km/h, and maximum speed. Electromyographic activity (EMG) along the BF and joint angular displacements were recorded with a 16-channel high-density EMG array and 3-D motion analysis, respectively. EMG data were normalized to maximal voluntary isometric contraction. Main Outcome Measures Normalized root-mean-square activity was calculated in the proximal, middle and distal muscle regions, and BF elongation was calculated using musculoskeletal modelling. Results Higher BF elongation and activity were observed in all regions with increasing speed. Activity in the proximal region was lower compared to the distal region at 15, 18 km/h and maximum speed, by 12, 18, and 35%, respectively. Conclusions Lower relative activity in the proximal region and greater proximal-distal differences in activity with increasing speed may indicate why HSIs occur at higher speeds, and mainly in the proximal region. Lower proximal activity may be associated with the higher elongation in this region during eccentric contractions that has been reported previously. Future studies are needed to examine whether players with higher within-muscle heterogeneity in muscle recruitment are at higher risk for HSI.
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