Secular and longitudinal physical activity changes in population‐based samples of children and adolescents

The aims of this study were to investigate whether physical activity (PA ) and sedentary time (ST ) in 9‐ and 15‐year‐olds differed between 2005‐2006 and 2011‐2012 (secular change), and to investigate changes in PA and ST from age 9 to 15 (longitudinal change). In 2005‐2006, we invited nationally representative samples of Norwegian 9‐ (n=1470) and 15‐year‐olds (n=1348) to participate. In 2011‐2012, we invited a new nationally representative sample of 9‐year‐olds (n=1945), whereas 15‐year‐olds (n=1759) were invited to participate either based on previous participation in 2005‐2006 or from a random sample of schools. We assessed PA and ST objectively using accelerometers. In 2011‐2012, both 9‐ and 15‐year‐olds spent more time sedentary (≥35.7 min/d, P <.001) and less time in light PA (≥35.2 min/d, P <.001) compared to their peers in 2005‐2006. Nine‐year‐old girls also spent less time in moderate‐to‐vigorous PA (MVPA ) (4.2 min/d, P =.041). In both age groups, the proportion accumulating an average of 60 min/d of MVPA did not differ between the two cohorts. From age 9 to 15, girls and boys decreased their time spent in LPA (≥106.7 min/d, P <.001) and in MVPA (≥20.8 min/d, P <.001). During the same period, ST increased by a mean of >2 h/d (P <.011). We observed an adverse secular change in PA from 2005‐2006 to 2011‐2012 among 9‐ and 15‐year‐olds, and a large decline in PA in the participants followed longitudinally from age 9 to 15 years.     

The response of cortical alpha activity to pain and neuromuscular changes caused by exercise‐induced muscle damage

Exercise‐induced muscle damage (EIMD) is characterized by pain, swelling, and shortening of the muscle; increased serum creatine kinase; decreased force output; and altered neuromuscular function. The aim of this study was to investigate the effects of EIMD to determine the relationship between the peripheral symptoms, neuromuscular changes, and delayed pain sensation during a submaximal movement of the biceps brachii on cortical alpha (α) activity. In contrast to the control (n = 12) group, the experimental (n = 16) group participated in an EIMD protocol, and both groups were monitored for 132 h post‐EIMD protocol. At 12 h, neuromuscular functioning was already disturbed while the sensation of pain was perceived, but not fully developed. Muscle pain scores in the experimental group peaked after 36 h with the lowest torque reported at 12 h. α‐1 activity increased significantly in the motor and somatosensory area 12 h post‐EIMD while α‐2 activity increased in the contralateral fronto‐central area. At 36 h, pain had further increased and neuromuscular function improved while α‐1 and α‐2 activities had decreased. We hypothesize that α‐1 activity over the motor and somatosensory cortex of the experimental group displays a compensatory increase in response to the changes in neuromuscular function during movement, while an increase in α‐2 activity is related to the suppression of pain experienced within the first 12 h.     

Ability to perform a single heel‐rise is significantly related to patient‐reported outcome after Achilles tendon rupture

This study evaluated the short‐term recovery of function after an acute Achilles tendon rupture, measured by a single‐legged heel‐rise test, with main emphasis on the relation to the patient‐reported outcomes and fear of physical activity and movement (kinesiophobia). Eighty‐one patients treated surgically or non‐surgically with early active rehabilitation after Achilles tendon rupture were included in the study. Patient's ability to perform a single‐legged heel‐rise, physical activity level, patient‐reported symptoms, general health, and kinesiophobia was evaluated 12 weeks after the injury. The heel‐rise test showed that 40 out of 81 (49%) patients were unable to perform a single heel‐rise 12 weeks after the injury. We found that patients who were able to perform a heel‐rise were significantly younger, more often of male gender, reported a lesser degree of symptoms, and also had a higher degree of physical activity at 12 weeks. There was also a significant negative correlation between kinesiophobia and all the patient‐reported outcomes and the physical activity level. The heel‐rise ability appears to be an important early achievement and reflects the general level of healing, which influences patient‐reported outcome and physical activity. Future treatment protocols focusing on regaining strength early after the injury therefore seem to be of great importance. Kinesiophobia needs to be addressed early during the rehabilitation process.     

Potential serious bias in National Clinical Databases with low degree of reported follow‐up

We identified reasons for the low follow‐up rate in the Danish Knee ligament Reconstruction Register (DKRR) and evaluated its influence on the data quality. All 946 primary ACL‐reconstructed patients in the Capital Region of Denmark during 2012 were identified in the databases of 8 participating hospitals. We studied the patient files and compared them to figures reported to the DKRR. 92.5% of the operated patients was registered in DKRR. The 1‐year follow‐up rate reported to DKRR was 33.4%, and 14.5% filled in patient reported outcomes (KOOS and Tegner) at 1 year. Only 65% had actually been invited for follow‐up, but among the patients who had been invited 91% were seen. 41% of existing follow‐up data was not reported. Contemporary technology and structured motivation should be introduced to increase validity of data in national clinical databases. Follow‐up >90% in the DKRR is realistic if patents are invited and reported. The unreported data is potentially a serious bias. It is suggested that data from clinics with low follow‐up should not be used in studies involving outcomes based on national databases because of risk of bias.     

The time course of endogenous erythropoietin,IL‐6, and TNFα in response to acute hypoxic exposures

Erythropoietin (EPO) rapidly decreases on return to sea level (SL) after chronic altitude exposure. Acute hypoxia may provide an additional stimulus to prevent the decline in EPO. Proinflammatory cytokines, interleukin‐6 (IL‐6), and tumor necrosis factor alpha (TNFα) have been shown to inhibit EPO production. Optimal normobaric hypoxic exposure has not been established; therefore, investigation of methods eliciting the greatest response in EPO to limit physiological stress is required. Eight men (age 27 ± 4 years, body mass 77.5 ± 9.0 kg, height 179 ± 6 cm) performed four passive exposures to different normobaric hypoxic severities [FiO₂: 0.209 (SL), FiO₂: ~0.135 (3600 m), FiO₂: ~0.125 (4200 m) and FiO₂: ~0.115 (4800 m)] in a hypoxic chamber for 2 h. Venous blood was drawn pre‐exposure and then at 1, 2, 4, 6, and 8 h to determine EPO concentration ([EPO]), IL‐6, and TNFα. During 4200 and 4800 m, [EPO] increased from 5.9 ± 1.5 to 8.1 ± 1.5 mU/mL (P = 0.009) and 6.0 ± 1.4 to 8.9 ± 2.0 mU/mL (P = 0.037), respectively, with [EPO] increase peaking at 4 h (2 h post‐exposure). There were no differences in IL‐6 or TNFα during or post‐exposure. Increased [EPO] was found 2 h post hypoxic exposure as result of 2 h of normobaric hypoxia ≥4200 m. There was no dose–response relationship in [EPO] between simulated hypoxia severities.     

Individual and combined effects of acute and chronic running loads on injury risk in elite Australian footballers

A model that takes into account the current workload, and the workload the athlete has been prepared for, as an acute:chronic workload ratio has been previously used as a novel way to monitor training load and injury risk. Fifty‐nine elite Australian football players from one club participated in this 2‐year study. Global Positioning System technology was used to provide information on running workloads of players. An injury was defined as any non‐contact “time‐loss” injury. One‐week (acute), along with 4‐week (chronic) workloads were calculated for a range of variables. The size of the acute workload in relation to the chronic workload was calculated as an acute:chronic workload ratio. An acute:chronic workload ratio of >2.0 for total distance during the in‐season was associated with a 5 to 8‐fold greater injury risk in the current [relative risk (RR) = 8.65, P = 0.001] and subsequent week (RR = 5.49, P = 0.016). Players with a high‐speed distance acute:chronic workload ratio of >2.0 were 5–11 times more likely to sustain an injury in the current (RR = 11.62, P = 0.006) and subsequent week (RR = 5.10, P = 0.014). These findings demonstrate that sharp increases in running workload increase the likelihood of injury in both the week the workload is performed, and the subsequent week.     

Factors associated with playing football after anterior cruciate ligament reconstruction in female football players

This study investigated whether player‐related factors (demographic, personality, or psychological factors) or the characteristics of the anterior cruciate ligament (ACL) injury were associated with the return to playing football in females after ACL reconstruction (ACLR). We also compared current knee function, knee related quality of life and readiness to return to sport between females who returned to football and those who had not returned. Females who sustained a primary ACL rupture while playing football and underwent ACLR 6–36 months ago were eligible. Of the 460 contacted, 274 (60%) completed a battery of questionnaires, and 182 were included a median of 18 months (IQR 13) after ACLR. Of these, 94 (52%) returned to football and were currently playing, and 88 (48%) had not returned. Multiple logistic regression analysis identified two factors associated with returning to football: short time between injury and ACLR (0–3 months, OR 5.6; 3–12 months OR 4.7 vs reference group > 12 months) and high motivation. Current players showed higher ratings for current knee function, knee‐related quality of life, and psychological readiness to return to sport (P < 0.001). Undergoing ACLR sooner after injury and high motivation to return to sports may impact a player's return to football after ACLR.     

Facilitation of quadriceps activation is impaired following eccentric exercise

Contracting the knee flexor muscles immediately before a maximum voluntary contraction (MVC) of knee extension increases the maximal force that the extensor muscles can exert. It is hypothesized that this phenomenon can be impaired by muscle fiber damage following eccentric exercise [delayed onset muscle soreness (DOMS)]. This study investigates the effect of eccentric exercise and DOMS on knee extension MVC immediately following a reciprocal‐resisted knee flexion contraction. Electromyography (EMG) was recorded from the knee extensors and flexors of 12 healthy men during knee extension MVCs performed in a reciprocal (maximal knee extension preceded by resisted knee flexion), and nonreciprocal condition (preceded by relaxation of the knee flexors). At baseline, knee extension MVC force was greater during the reciprocal condition (P < 0.001), whereas immediately after, 24 and 48 h after eccentric exercise, the MVC force was not different between conditions. Similarly, at baseline, the EMG amplitude of the quadriceps during the MVC was larger for the reciprocal condition (P < 0.001). However, immediately after, 24 and 48 h postexercise the EMG amplitude was similar between conditions. In conclusion, eccentric exercise abolished the facilitation of force production for the knee extensors, which normally occurs when maximum knee extension is preceded by activation of the knee flexors.     

Is physical education an effective way to increase physical activity in children with lower cardiorespiratory fitness?

Several findings revealed the importance of accruing moderate and vigorous physical activity (MVPA) to improve health. Physical education (PE) may play an important role on promoting children's MVPA. However, it remains unknown whether PE might be effective when increasing physical activity (PA) levels in children with lower cardiorespiratory fitness (CRF). Therefore, the aim of this study was to assess children's PA during PE and during days with and without PE with a special focus on CRF status. One hundred and fifty Spanish children and adolescents from 3rd to 12th grade were recruited. PA levels were assessed with GT3X accelerometers. Peak oxygen uptake (VO_2peak) was estimated using a portable breath by breath Metamax 3B. Participants were classified as healthy aerobic fitness (HAF) and unhealthy aerobic fitness (UHAF) according to standardized cut‐off point criteria. During PE, students with HAF accrued more MVPA than those with UHAF (8.7 vs 5.7 min/session; P ≤ 0.001). MVPA was higher on PE days than days without for both UHAF (50.0 vs 42.7 min/day; P ≤ 0.05) and HAF students (56.9 vs 49.4 min/day; P ≤ 0.05). Although less active during PE, students with lower CRF accumulated more MVPA and total PA on PE days than days without PE. An increase in PE days might be a smart policy to raise the recommended PA levels, regardless of CRF status.     

Muscular and neuromuscular control following soccer‐specific exercise in male youth: Changes in injury risk mechanisms

Poor neuromuscular control has been proposed as a risk factor for non‐contact injuries, thus this study aimed to explore the effects of soccer‐specific fatigue on leg muscle activation, reactive strength, leg stiffness, and functional hamstring/quadriceps ratio (H/Q_FUNC) in elite male youth soccer players. Outcome measures were determined in 18 youth players (age 14.4 ± 0.5 years; stature 169.4 ± 9.9 cm; mass 59.3 ± 8.9 kg; maturity offset 0.86 ± 0.88 years) pre and post simulated soccer match play (SAFT⁹⁰). There was no fatigue‐related change in the H/Q_FUNC; however, reactive strength and leg stiffness were both compromised (P < 0.001) after soccer‐specific fatigue. Muscle activation was also locally compromised (P < 0.001) in the medial hamstring and quadriceps but not in the lateral muscles. Where statistically significant changes were observed, the effect sizes ranged from small to large (0.33–0.97). Compromised stiffness when fatigue is present suggests an increased yielding action, greater ground contact times, greater center of mass displacement, and less efficient movement when the limb comes into contact with the ground. This combined with a reduction in medial quadriceps muscle activation may reflect poor kinetic chain control at the hip and an increase in knee injury risk.     

Correlates of children's compliance with moderate‐to‐vigorous physical activity recommendations: a multilevel analysis

This study aimed to investigate the association between individual and school characteristics associated with the number of school days children comply with moderate‐to‐vigorous physical activity (MVPA) recommendations. Sample comprises 612 Portuguese children, aged 9–11 years, from 23 schools. Time spent in MVPA was measured by accelerometry, while individual‐level correlates were obtained by anthropometry and questionnaires. School‐level variables were collected by questionnaire, and accelerometer wear time and season were also considered. Maximum likelihood estimates of model parameters were obtained via a multilevel analysis with children as level‐1, and school as level‐2. Children who spent more time in sedentary activities and girls were less likely to comply with MVPA/daily. More mature children and those who use active transportation to school were more likely to attain the PA recommendation. Furthermore, greater accelerometer wear time and spring season increased the chance to achieve the recommended MVPA. In terms of school‐level correlates, a greater number of available facilities was negatively associated with children MVPA compliance. Given the set of variables, our results showed that individual characteristics seem to be more relevant for children's compliance rates with PA/day than school context variables, which should be taken into account in the implementation of school policies and practices.     

Prevalence and severity of hip and groin pain in sub‐elite male football: a cross‐sectional cohort study of 695 players

The purpose of this study was twofold: (a) to investigate the prevalence of hip and groin pain in sub‐elite male adult football in Denmark and (b) to explore the association between prevalence and duration of hip and groin pain in the previous season with the Copenhagen Hip and Groin Outcome Score (HAGOS) in the beginning of the new season. In total 695 respondents from 40 teams (Division 1–4) were included. Players completed in the beginning of the new season (July–Sept 2011) a self‐reported paper questionnaire on hip and/or groin pain during the previous season and HAGOS. In total 49% (95% CI: 45–52%) reported hip and/or groin pain during the previous season. Of these, 31% (95% CI: 26–36%) reported pain for >6 weeks. Players with the longest duration of pain during the previous season had the lowest HAGOS scores, when assessed at the beginning of the new season, P < 0.001. This study documents that half of sub‐elite male adult football players report pain in the hip and/or groin during a football season. The football players with the longest duration of pain in previous season displayed the lowest HAGOS scores in the beginning of the new season.     

Evaluation of raw acceleration sedentary thresholds in children and adults

The aim was to develop sedentary (sitting/lying) thresholds from hip and wrist worn raw tri‐axial acceleration data from the ActiGraph and GENEActiv, and to examine the agreement between free‐living time spent below these thresholds with sedentary time estimated by the activPAL. Sixty children and adults wore an ActiGraph and GENEActiv on the hip and wrist while performing six structured activities, before wearing the monitors, in addition to an activPAL, for 24 h. Receiver operating characteristic (ROC) curves were used to determine sedentary thresholds based on activities in the laboratory. Agreement between developed sedentary thresholds during free‐living and activPAL were assessed by Bland‐Altman plots and by calculating sensitivity and specificity. Using laboratory data and ROC‐curves showed similar classification accuracy for wrist and hip thresholds (Area under the curve = 0.84–0.92). Greatest sensitivity (97–98%) and specificity (74–78%) were observed for the wrist thresholds, with no large differences between brands. During free‐living, Bland‐Altman plots showed large mean individual biases and 95% limits of agreement compared with activPAL, with smallest difference for the ActiGraph wrist threshold in children (+30 min, P = 0.3). Sensitivity and specificity for the developed thresholds during free‐living were low for both age groups and for wrist (Sensitivity, 68–88%, Specificity, 46–59%) and hip placements (Sensitivity, 89–97%, Specificity, 26–34%). Laboratory derived sedentary thresholds generally overestimate free‐living sedentary time compared with activPAL. Wrist thresholds appear to perform better than hip thresholds for estimating free‐living sedentary time in children and adults relative to activPAL, however, specificity for all the developed thresholds are low.