Balance Training Under Fatigue: A Randomized Controlled Trial on the Effect of Fatigue on Adaptations to Balance Training.

ABSTRACT: Keller, M, Lichtenstein, E, Roth, R, and Faude, O. Balance training under fatigue: a randomized controlled trial on the effect of fatigue on adaptations to balance training. J Strength Cond Res 38(2): 297-305, 2024-Balance training is an effective means for injury prevention in sports. However, one can question the existing practice of putting the balance programs at the start of a training session (i.e., train in an unfatigued state) because the occurrence of injuries has been associated with fatigue. Therefore, the aim of this study was to assess the influence of balance training in a fatigued or an unfatigued state on motor performance tested in fatigued and unfatigued conditions. Fifty-two, healthy, active volunteers (28.0 years; 19 women) were randomly allocated to 1 of 3 different training groups. The BALANCE group completed 6 weeks of balance training. The other 2 groups completed the identical balance tasks either before (BALANCE-high-intensity interval training [HIIT]) or after (HIIT-BALANCE) a HIIT session. Thus, these groups trained the balance tasks either in a fatigued or in an unfatigued state. In PRE and POST tests, balance (solid ground, soft mat, wobble board) and jump performance was obtained in fatigued and unfatigued states. Balance training resulted in reduced sway paths in all groups. However, the linear models revealed larger adaptations in BALANCE-HIIT and BALANCE when compared with HIIT-BALANCE ( d = 0.22-0.71). These small to moderate effects were-despite some uncertainties-consistent for the "unfatigued" and "fatigued" test conditions. The results of this study revealed for the first time that balance training under fatigue results in diminished adaptations, even when tested in a fatigued state. Therefore, the data indicate that balance training should be implemented at the start of a training session or in an unfatigued state.

Secular change in selected motor performance parameters and BMI in Swiss primary school children from 2014-2021: The Sportcheck+ study.

It is important to monitor secular trends in children's motor performance, as healthy and physically active children are more likely to become healthy and physically active adults. However, studies with regular and standardized monitoring of motor performance in childhood are scarce. Additionally, the impact of COVID-19 mitigation measures on secular trends is unknown. This study describes secular changes in balancing backwards, jumping sidewards, 20-m sprint, 20-m Shuttle Run Test (SRT) and anthropometric data in 10'953 Swiss first graders from 2014 to 2021. Multilevel mixed-effects models were used to estimate secular trends for boys vs. girls, lean vs. overweight and fit vs. unfit children. The potential influence of COVID-19 was also analysed. Balance performance decreased (2.8% per year), whereas we found improvements for jumping (1.3% per year) and BMI (-0.7% per year). 20-m SRT performance increased by 0.6% per year in unfit children. Children affected by COVID-19 measures had an increased BMI and were more overweight and obese, but motor performance was mostly higher. In our sample, secular changes in motor performance show promising tendencies from 2014 to 2021. The effects of COVID-19 mitigation measures on BMI, overweight and obesity should be monitored in additional birth cohorts and follow-up studies.

Acute Leg and Trunk Muscle Fatigue Differentially Affect Strength, Sprint, Agility, and Balance in Young Adults.

ABSTRACT: Roth, R, Donath, L, Zahner, L, and Faude, O. Acute leg and trunk muscle fatigue differentially affect strength, sprint, agility, and balance in young adults. J Strength Cond Res 35(8): 2158-2164, 2021-How important leg or trunk muscles are for balance and sprint performance is still unexplored. Therefore, we separately fatigued the leg and trunk musculature and examined their contribution to strength, balance, sprint, and agility performance. Twenty-four healthy adults (12 women; age 22.9 [SD: 2.6] years; body mass 59 [10] kg; height 1.65 [0.09] m; and 12 men; age 22.7 [3.0] years; body mass 78 [9] kg; height 1.81 [0.06] m; at least 3 training sessions/week for at least 90 minutes) underwent a leg and a trunk fatigue procedure, each of 20-minute duration and a control condition at rest in a randomized order. Each condition was conducted individually on 3 separate days. Isokinetic leg and trunk strength, as well as static and dynamic balance, sprint, agility, and prone plank endurance, were assessed before and after each fatiguing protocol. Before assessment, a familiarization was conducted. Pairwise magnitude-based inference analyses showed likely relevant deterioration in leg (probability >87%; 0.36 < standardized mean differences [SMDs] < 0.92) and trunk (>88%, 0.28 < SMD < 0.74) fatigue procedures for all motor test parameters compared with the control condition, except for the 20-m sprint after the trunk fatigue procedure. Isokinetic strength testing revealed a large loss of strength in leg fatigue (particularly knee extension, 78%, SMD = 0.24) and trunk fatigue (trunk flexion, 100%, SMD = 1.36). Acute fatigue of leg and trunk muscles decreases performance in relevant measures of strength, balance, sprint, and agility. The impact of leg fatigue compared with trunk fatigue was larger in almost all measurements.

Trunk muscle activity during different types of low weighted squat exercises in normal and forefoot standing conditions.

Squats are considered a useful basic exercise for trunk muscle activation. To gain knowledge about trunk muscle activity patterns depending on the barbell position in beginners, we examined squats with low weights in the back, front, and overhead position. METHODS: Twelve healthy adults (6 women/6 men, age: 29.1 (SD 8.0) y, height: 173.4 (6.9) cm, body mass: 70.1 (9.1) kg) randomly performed the three barbell squats in normal and in forefoot standing. Surface electromyography from external (EO) and internal oblique, rectus abdominis, and erector spinae (ES) was recorded. The centre of pressure path length (CoP) and the motion of the lumbar spine were captured. RESULTS: The overhead squat revealed the highest percent muscle activity, where EO (p = 0.009) and ES (p = 0.03) showed the greatest activity. Forefoot standing did not change overall trunk muscle activities (.05< Hedges' g <.29, 0.17 < p < 0.95) although longer CoP path length (.45 < g < 1.3, p < 0.05) was measured. CONCLUSIONS: Squat exercises with low weight are useful to activate trunk muscles. Activity increases with the difficulty of the squat by frontal or overhead loading, but not by standing on the forefoot. The low weighted squat can target well core muscle activity in training with beginners or in rehabilitation.

Functional aging in health and heart failure: the COmPLETE Study.

BACKGROUND: Cardiovascular (CV) diseases including heart failure are the leading causes of morbidity, with age being the primary risk factor. The combination of age-related organic functional impairment and reduced physical fitness can drastically impact an individual's healthspan. One's lifespan can potentially be prolonged by the preservation or improvement of physical fitness. However, it remains unclear as to which biomarkers are most suitable for distinguishing between healthy aging and the impaired organ function associated with heart failure. Therefore, a comprehensive assessment of the components of physical fitness and CV function will be performed to identify the most important factors contributing to aging in relation to both health and disease. METHODS: This cross-sectional investigation will consist of two parts: COmPLETE-Health (C-Health) and COmPLETE-Heart (C-Heart). C-Health will examine the aging trajectories of physical fitness components and CV properties in a healthy population sample aged between 20 and 100 years (n = 490). Separately, C-Heart will assess the same markers in patients at different stages of chronic heart failure (n = 80). The primary outcome to determine the difference between C-Health and C-Heart will be cardiorespiratory fitness as measured by cardiopulmonary exercise testing on a bicycle ergometer. Secondary outcomes will include walking speed, balance, isometric strength, peak power, and handgrip strength. Physical activity as a behavioural component will be assessed objectively via accelerometry. Further, CV assessments will include pulse wave velocity; retinal, arterial, and venous diameters; brachial and retinal arterial endothelial function; carotid intima-media thickness; and systolic and diastolic function. The health distances for C-Health and C-Heart will be calculated using the methodology based on statistical (Mahalanobis) distance applied to measurements of quantitative biomarkers. DISCUSSION: This research seeks to identify physical fitness and CV biomarkers that best resemble underlying CV risk with age. Further, it will examine which physical fitness markers are impaired most in heart failure. The presented integrative approach could define new recommendations for diagnostic guidance in aging. Ultimately, this study is expected to offer a better understanding of which functional characteristics should be specifically targeted in primary and secondary prevention to achieve an optimal healthspan.

Ankle muscle activity modulation during single-leg stance differs between children, young adults and seniors.

PURPOSE: Incomplete maturation and aging-induced declines of the neuromuscular system affect postural control both in children and older adults and lead to high fall rates. Age-specific comparisons of the modulation of ankle muscle activation and behavioral center of pressure (COP) indices during upright stance have been rarely conducted. The objective of the present study was to quantify aging effects on a neuromuscular level. Thus, surface electromyography (SEMG) modulation and co-activity of ankle muscles during single-leg standing was compared in healthy children, young adults and seniors. METHODS: Postural steadiness (velocity and mean sway frequency of COP), relative muscle activation (SEMG modulation) and co-activation of two ankle muscles (tibialis anterior, TA; soleus, SO) were examined during single-leg stance in 19 children [age, 9.7 (SD 0.5) years], 30 adults [23.3 (1.5) years] and 29 seniors [62.7 (6.1) years]. RESULTS: Velocity of COP in medio-lateral and anterior-posterior directions, mean sway frequency in anterior-posterior direction, relative muscle activation (TA and SO) and co-activation revealed large age effects (P < 0.003, η p2 > 0.14). Post-hoc comparisons indicated higher COP velocities, anterior-posterior frequencies, relative SO activation and co-activation in children and seniors when compared with adults. Relative TA activation was higher in children and adults compared with seniors (P < 0.001). CONCLUSIONS: Increased postural sway in children and seniors seems to be counteracted with higher TA/SO co-activity and SO modulation. However, TA modulation is higher in children and adults, whereas seniors' TA modulation capacity is diminished. An aging-induced decline of TA motor units might account for deteriorations of TA modulation in seniors.

Exercise-induced trunk fatigue decreases double poling performance in well-trained cross-country skiers.

PURPOSE: To examine the effects of exercise-induced trunk fatigue on double poling performance, physiological responses and trunk strength in cross-country skiers. METHODS: Sixteen well-trained male cross-country skiers completed two identical pre- and post-performance tests, separated by either a 25-min trunk fatiguing exercise sequence or rest period in a randomized, controlled cross-over design. Performance tests consisted of a maximal trunk flexion and extension test, followed by a 3-min double poling (DP) test on a ski ergometer. RESULTS: Peak torque during isometric trunk flexion (- 66%, p < .001) and extension (- 7.4%, p = .03) decreased in the fatigue relative to the control condition. Mean external power output during DP decreased by 14% (p < .001) and could be attributed both to reduced work per cycle (- 9%, p = .019) and a reduced cycle rate (- 6%, p = .06). Coinciding physiological changes in peak oxygen uptake (- 6%, p < .001) and peak ventilation (- 7%, p < .001) could be observed. Skiers chose a more even-pacing strategy when fatigued, with the performance difference between fatigue and control condition being most prominent during the first 2 min of the post-test. CONCLUSIONS: In well-trained cross-country skiers, exercise-induced trunk fatigue led to a substantial decrease in DP performance, caused by both decreased work per cycle and cycle rate and accompanied by reduced aerobic power. Hence, improved fatigue resistance of the trunk may therefore be of importance for high-intensity DP in cross-country skiing.

Muscle Activation and Performance During Trunk Strength Testing in High-Level Female and Male Football Players.

For performance and injury prevention in sport, core strength and endurance are focused prerequisites. Therefore we evaluated characteristics of trunk muscle activation and performance during strength-endurance related trunk field tests. Strength-endurance ability, as total time to failure, and activation of trunk muscles was measured in 39 football players of the highest German female football league (Bundesliga) (N = 18, age: 20.7 y [SD 4.4]) and the highest national male under-19 league (N = 21, age: 17.9 y [0.7]) in prone plank, side plank, and dorsal position. Maximal isometric force was assessed during trunk extension and flexion, rotation, and lateral flexion to normalize EMG and to compare with the results of strength-endurance tests. For all positions of endurance strength tests, a continuous increase in normalized EMG activation was observed (P < .001). Muscle activation of the rectus abdominis and external oblique in prone plank position exceeded the maximal voluntary isometric contraction activation, with a significantly higher activation in females (P = .02). We conclude, that in the applied strength-endurance testing, the activation of trunk muscles was high, especially in females. As high trunk muscle activation can infer fatigue, limb strength can limit performance in prone and side plank position, particularly during high trunk muscle activation.

Does a single session of high-intensity interval training provoke a transient elevated risk of falling in seniors and adults?

BACKGROUND: Balance and strength training can reduce seniors' fall risk up to 50%. Available evidence suggests that acute bouts of neuromuscular and endurance exercise deteriorate postural control. High-intensity endurance training has been successfully applied in different populations. Thus, it seemed valuable to examine the acute effects of high-intensity interval training (HIIT) on neuromuscular performance in seniors and young adults. OBJECTIVE: The acute impact of a HIIT session on balance performance and muscle activity after exercise cessation and during post-exercise recovery was examined in young and old adults. We intended to investigate whether a transient exercise-induced fall-risk may occur in both groups. METHODS: 20 healthy seniors (age 70 (SD 4) years) and young adults (age 27 (SD 3) years) were examined on 3 days. After exhaustive ramp-like treadmill testing in order to determine maximal heart rate (HRmax) on the first day, either a 4 × 4 min HIIT at 90% of HRmax or a control condition (CON) was randomly performed on the second and third day, respectively. Balance performance (postural sway) was assessed during single limb stance with open eyes (SLEO) and double limb stance with closed eyes (DLEC). EMG was recorded for the soleus (SOL), anterior tibialis (TIB), gastrocnemius (GM) and peroneus longus (PL) muscles at the dominant leg. All measures were collected before, immediately as well as 10, 30 and 45 min after HIIT and CON, respectively. RESULTS: Compared to CON, HIIT induced significant increases of postural sway immediately after exercise cessation during SLEO in both groups (adults: p < 0.001, Δ = +25% sway; seniors: p = 0.007, Δ = +15% sway). Increased sway during DLEC was only found for seniors immediately and 10 min after HIIT (post: p = 0.003, Δ = +14% sway, 10 min post: p = 0.004, Δ = +18% sway). Muscle activity was increased during SLEO for TIB until 10 min post in seniors (0.008 < p < 0.03) and immediately after HIIT in adults (p < 0.001). CONCLUSION: HIIT training may cause an acute 'open-fall-window' with a transient impairment of balance performance for at least 10 min after exercise cessation in both groups. Occluded vision in seniors seems to prolong this period up to 30 min. Thus, the advantage of HIIT with regard to time efficiency seems debatable when considering transient HIIT-induced impairments of neuromuscular function.

Different ankle muscle coordination patterns and co-activation during quiet stance between young adults and seniors do not change after a bout of high intensity training.

BACKGROUND: Available evidence suggests that young adults and seniors use different strategies to adjust for increasing body sway during quiet standing. Altered antagonist muscle co-activation and different ankle muscle coordination patterns may account for this finding. Consequently, we aimed at addressing whether aging leads to changes in neuromuscular coordination patterns as well as co-activation during quiet stance. We additionally investigated whether a bout of high intensity interval training additionally alters these patterns. METHODS: Twenty healthy seniors (age: 70 ± 4 y) and twenty young adults (age: 27 ± 3 y) were enrolled in the present study. In between the testing procedures, four consecutive high-intensity intervals of 4 min duration at a target exercise intensity of 90 to 95% HRmax were completed on a treadmill. The total center of pressure (COP) path length displacement served as standing balance performance outcome. In order to assess ankle muscle coordination patterns, amplitude ratios (AR) were calculated for each muscle (e.g. tibialis anterior (TA) [%] = (TA × 100)/(gastrocnemius medialis (GM) + soleus (SOL) + peroneus longus (PL) + TA). The co-activation was calculated for the SOL and TA muscles computing the co-activation index (CAI = 2 × TA/TA + SOL). RESULTS: Seniors showed an inverted ankle muscle coordination pattern during single limb stance with eyes open (SLEO), compared to young adults (rest: GM, S: 15 ± 8% vs Y: 24 ± 9%; p = 0.03; SOL, S: 27 ± 14% vs Y: 37 ± 18%; p = 0.009; TA, S: 31 ± 13% vs Y: 13 ± 7%; p = 0.003). These patterns did not change after a high-intensity training session. A moderate correlation between amplitude ratios of the TA-contribution and postural sway was observed for seniors during SLEO (r = 0.61). Ankle co-activation was twofold elevated in seniors compared to young adults during SLEO (p < 0.001). These findings were also not affected by high intensity training. CONCLUSION: Increased ankle co-activation in the anterior-posterior plane and inverted ankle muscle coordination pattern merely occurred during single-leg stance. Seniors with decreased postural control showed higher TA contributions during SLEO. These neuromuscular changes are not affected by acute intermittent high intensity aerobic exercise.

Transfer effects of fall training on balance performance and spatiotemporal gait parameters in healthy community-dwelling older adults: a pilot study.

This study examined transfer effects of fall training on fear of falling (Falls Efficacy Scale-International [FES-I]), balance performance, and spatiotemporal gait characteristics in older adults. Eighteen community-dwelling older adults (ages 65-85) were randomly assigned to an intervention or control group. The intervention group completed 12 training sessions (60 min, 6 weeks). During pre- and posttesting, we measured FES-I, balance performance (double limb, closed eyes; single limb, open eyes; double limb, open eyes with motor-interfered task), and gait parameters (e.g., velocity; cadence; stride time, stride width, and stride length; variability of stride time and stride length) under single- and motor-interfered tasks. Dual tasks were applied to appraise improvements of cognitive processing during balance and gait. FES-I (p = .33) and postural sway did not significantly change (0.36 < p < .79). Trends toward significant interaction effects were found for step width during normal walking and stride length variability during the motor dual task (p = .05, ηp 2 = .22). Fall training did not sufficiently improve fear of falling, balance, or gait performance under single- or dual-task conditions in healthy older adults.

One-leg standing performance and muscle activity: are there limb differences?

The purpose of this study was to compare static balance performance and muscle activity during one-leg standing on the dominant and nondominant leg under various sensory conditions with increased levels of task difficulty. Thirty healthy young adults (age: 23 ± 2 years) performed one-leg standing tests for 30 s under three sensory conditions (ie, eyes open/firm ground; eyes open/ foam ground [elastic pad on top of the balance plate]; eyes closed/firm ground). Center of pressure displacements and activity of four lower leg muscles (ie, m. tibialis anterior [TA], m. soleus [SOL], m. gastrocnemius medialis [GAS], m. peroneus longus [PER]) were analyzed. An increase in sensory task difficulty resulted in deteriorated balance performance (P < .001, effect size [ES] = .57-2.54) and increased muscle activity (P < .001, ES = .50-1.11) for all but two muscles (ie, GAS, PER). However, regardless of the sensory condition, one-leg standing on the dominant as compared with the nondominant limb did not produce statistically significant differences in various balance (P > .05, ES = .06-.22) and electromyographic (P > .05, ES = .03-.13) measures. This indicates that the dominant and the nondominant leg can be used interchangeably during static one-leg balance testing in healthy young adults.

Muscle Activity and Kinematics During Three Hamstring Strengthening Exercises Compared to Sprinting: A Cross-Sectional Study.

Background: During sprinting, the biceps femoris long head predominantly gets injured, while hamstring strengthening exercises predominantly activate the semitendinosus more effectively. Understanding how joint dominance influences hamstring activity may offer clarity on appropriate exercise selection in strengthening programs. Purpose: This study compared three hip-dominant hamstring exercises: the rocker, perpetuum mobile fast and slow (PMfast and PMslow) and the Nordic Hamstring exercise (NHE) on their potential to simulate sprint-like activity and kinematics. Methods: Muscle activity of the posterior kinetic chain (biceps femoris, semitendinosus, gluteus maximus, and medial gastrocnemius) was measured with surface electromyography (sEMG) during the exercises and treadmill running at 75% of the individual maximal sprint velocity in male athletes. sEMG data were normalized to maximal sprinting. 3D-motion capture was employed to assess hip and knee angles. Results: Eight male athletes were included (age: 24.0 years ± SD 2.9; body mass: 76.8 kg ± 7.7; height: 1.79 m ± 0.08). Greater activity of the hamstrings occurred during the explosive exercises ranging from 63.9% [95%CI: 56.3-71.5%] (rocker) to 49.0% [95%CI: 40.4-57.6%] (PMfast) vs. 34.0% [95%CI: 29.1-38.9%] (NHE) to 32.1% [95%CI: 26.9-37.3%] (PMslow). The rocker showed greatest hamstring and gluteus maximus activity. Biceps femoris consistently showed greater activity than the semitendinosus across all exercises in peak (mean difference: 0.16, [95%CI: 0.07-0.26]) and average (mean difference: 0.06, [95%CI: 0.01-0.11]) activity. PMfast, PMslow and NHE demonstrated less hip flexion angle at peak hamstring activity than the rocker and high-speed running and every exercise showed less hamstring elongation stress than during high-speed running. Discussion: Hamstring activity is comparable to high-intensity treadmill running for NHE and PMslow, and greater for the rocker and PMfast. Gluteus maximus activity varied, with the rocker and PMfast showing greater activity than in sprinting. All examined exercises demonstrated their peak activity at short hamstring muscle length. Level of evidence: 3b.

Physiological Profiles of Male and Female CrossFit Athletes.

OBJECTIVE: To (1) establish extensive physiological profiles of highly trained CrossFit® athletes using gold-standard tests and (2) investigate which physiological markers best correlate with CrossFit Open performance. METHODS: This study encompassed 60 participants (30 men and 30 women), all within the top 5% of the CrossFit Open, including 7 CrossFit semifinalists and 3 CrossFit Games finalists. Isokinetic dynamometers were employed to measure maximum isometric and isokinetic leg and trunk strength. Countermovement-jump height and maximum isometric midthigh-pull strength were assessed on a force plate. Peak oxygen uptake (VO2peak) was measured by a cardiopulmonary exercise test, and critical power and W' were evaluated during a 3-minute all-out test, both on a cycle ergometer. RESULTS: Male and female athletes' median (interquartile range) VO2peak was 4.64 (4.43, 4.80) and 3.21 (3.10, 3.29) L·min-1, critical power 314.5 (285.9, 343.6) and 221.3 (200.9, 238.9) W, and midthigh pull 3158 (2690, 3462) and 2035 (1728, 2347) N. Linear-regression analysis showed strong evidence for associations between different anthropometric variables and CrossFit Open performance in men and women, whereas for markers of cardiorespiratory fitness such as VO2peak, this was only true for women but not men. Conventional laboratory evaluations of strength, however, manifested minimal evidence for associations with CrossFit Open performance across both sexes. CONCLUSIONS: This study provides the first detailed insights into the physiology of high-performing CrossFit athletes and informs training optimization. Furthermore, the results emphasize the advantage of athletes with shorter limbs and suggest potential modifications to CrossFit Open workout designs to level the playing field for athletes across different anthropometric characteristics.

Balance and gait performance after maximal and submaximal endurance exercise in seniors: is there a higher fall-risk?

Impaired balance and gait performance increase fall-risk in seniors. Acute effects of different exercise bouts on gait and balance were not yet addressed. Therefore, 19 healthy seniors (10 women, 9 men, age: 64.6 ± 3.2 years) were examined on 3 days. After exhaustive treadmill testing, participants randomly completed a 2-km treadmill walking test (76 ± 8 % VO(2max)) and a resting control condition. Standing balance performance (SBALP) was assessed by single limb-eyes opened (SLEO) and double limb-eyes closed (DLEC) stance. Gait parameters were collected at comfortable walking velocity. A condition × time interaction of center of pressure path length (COP(path)) was observed for both balance tasks (p < 0.001). Small (Cohen's d = 0.42, p = 0.05) and large (d = 1.04, p < 0.001) COP(path) increases were found after 2-km and maximal exercise during DLEC. Regarding SLEO, slightly increased COP(path) occurred after 2-km walking (d = 0.29, p = 0.65) and large increases after exhaustive exercise (d = 1.24, p < 0.001). No significant differences were found for gait parameters. Alterations of SBALP after exhaustive exercise might lead to higher fall-risk in seniors. Balance changes upon 2-km testing might be of minor relevance. Gait is not affected during single task walking at given velocities.

Combined strength and power training in high-level amateur football during the competitive season: a randomised-controlled trial.

We aimed to analyse the effects of combined strength and power training during the competitive season on physical fitness in high-level amateur football players. Sixteen male players (22.5 (SD 2.5) years, 1.79 (0.05) m, 76.8 (6.1) kg) from one team were randomly assigned to either a strength training (ST, N = 8) or a control (CON, N = 8) group. ST conducted lower extremity resistance exercises combined with plyometrics and/or sprints 2 × 30 min per week for 7 weeks. CON performed technical-tactical training during the same time period. Before and after training several physical fitness parameters were assessed: one-repetition maximum (1-RM, half squat), isometric peak strength and rate of force development (RFD, leg press), jump height (countermovement, CMJ, drop jump, DJ), sprint times, agility, and intermittent endurance. Large significant test × group interactions were found for 1-RM, CMJ, and DJ reactivity index with increases in CT relative to CON(+11 to 18%). Although not significant (P < 0.20), likely practically relevant effects were observed for isometric peak strength and RFD (+24 to 29%). We found no relevant interaction effects for agility, sprint times, and intermittent endurance. A 7-week in-season combined strength and power training program can improve relevant strength and jump parameters in high-level amateur football players.

Learning a new balance task: The influence of prior motor practice on training adaptations.

Prior motor experience is thought to aid in the acquisition of new skills. However, studies have shown that balance training does not promote learning of a subsequent balance task. These results stand in contrast to the learning-to-learn paradigm, which is well described for other tasks. We therefore tested if a coordinative affinity between tasks is needed to achieve a learning-to-learn for balance control. Three groups trained different motor tasks during training phase1 (coordination ladder (COOR); bipedal wobble board (2WB); single-leg wobble board (1WB)). During training phase2, all groups trained a tiltboard balance task. Task-specific and transfer effects were evaluated for phase1. A potential learning-to-learn effect was evaluated by comparing the acquisition rates from phase2 for the tiltboard task that was used for training and testing. The results indicate task-specific adaptations after phase1 for 1WB. In contrast, 2WB showed similar improvements than 1WB and COOR (effect sizes: -0.31 to -0.38) when tested on the wobble board with bipedal stance indicating no task-specific improvement for 2WB. For phase2, the linear regression analysis showed larger adaptations for 1WB and 2WB when compared to COOR. This effect implies some uncertainty due to overlapping confidence intervals. Task-specific adaptations after phase1 were found for 1WB but not 2WB. It is discussed that the difficulty of the training task could explain these contrasting results. During phase2, larger adaptations were found for both groups that trained balance tasks during phase1. Thus, despite some uncertainty, prior balance training appears to promote adaptations of a subsequently learned balance task.HighlightsPrior balance training augments the learning of a new balance task if the two tasks share certain coordinative features.The concept of "learning to learn" can probably be applied to postural control, although further studies are needed.Balance training results (partly) in task-specific adaptations with no immediate transfer to other (but unrelated) balance tasks.

Contribution of different strength determinants on distinct phases of Olympic rowing performance in adolescent athletes.

Aerobic metabolism dominates Olympic rowing, but research on the relative contribution of strength and power demands is limited. This study aimed to identify the contribution of different strength determinants for distinct phases of rowing ergometer performance. The cross-sectional analysis comprised of 14 rowing athletes (4 female, 10 male, age: 18.8 ± 3.0y, 16.9 ± 2.2y). Measurements included anthropometrics, maximal strength of leg press, trunk extension and flexion, mid-thigh pull (MTP) and handgrip strength, VO2max, and a 2000 m time trial, where peak forces at the start, middle and end phase were assessed. Additionally, rate of force development (RFD) was assessed during the isometric leg press and MTP with intervals of 150, 350 ms and 150, 300 ms, respectively. Stepwise regression models for ergometer performance showed that the start phase was mainly explained by maximal trunk extension and RFD 300 ms of MTP (R2 = 0.91, p < 0.001) and the middle section by VO2max, maximal leg press strength and sitting height (R2 = 0.84, p < 0.001). For the end phase, a best fit was observed for trunk flexion, RFD 350 ms of leg press, body height and sex (R2 = 0.97 p < 0.001), whereas absolute VO2max, trunk flexion and sex explained variance over the entire 2000 m time trial (R2 = 0.98, p < 0.001). It appears that for the high acceleration in the start phase, force transmission through maximum strength for trunk extension is essential, while fast power production along the kinetic chain is also relevant. Additionally, the results support that maximal force complements the reliance on VO2max. Further intervention studies are needed to refine training recommendations.

This study highlights the importance of the neuromuscular system for rowing performance, which has to be considered in addition to the well-known factors VO₂max, anthropometry and sex.For overall 2000 m rowing performance, maximal leg strength appears to complement the reliance on VO₂max for maintenance of force production.For efficient force transmission in the start phase, maximal strength of trunk extension and a fast power production along the kinetic chain of legs, trunk and arms are essential, while towards the end of the race isometric trunk flexion and rate of force development of leg press appear to be important.

Translating scientific recommendations into reality: a feasibility study using group-based high-intensity functional exercise training in adolescents with cerebral palsy.

PURPOSE: To examine the feasibility and effects of a functional high-intensity exercise intervention performed in a group-setting on functionality, cardiovascular health and physical performance in adolescents with cerebral palsy (CP). METHODS: Ten adolescents with a diagnosis of CP (2 females; 16.6 ± 3.4 years; GMFCS: I-II) participated in a 12-week training intervention, containing progressive resistance training using free weights and high-intensity workouts twice a week. The six-minute walking test, arterial stiffness and physical performance (strength and power tests) were measured before and after the intervention. RESULTS: No adverse events were reported. We measured small increases in the six-minute walking test (Δ = 28.8 m, 95% CI [-1.78;52.7]; g = 0.34 [-0.04;0.72]) and a small reduction in arterial stiffness (Δ = -4.65% [-10.90;1.25]; g = -0.46 [-1.36;0.21]). All measures of physical performance increased (0.24 ≤ g ≤ 0.88). CONCLUSION: Functional training with free weights in high-functioning adolescents with CP is safe and effective in increasing parameters of physical performance and cardiovascular health. Positively influenced indicators of everyday independence (i.e. strength parameters) showed a transfer into movements of daily life. Concerns about adverse events through high-intensity training in adolescents with CP appear unjustified when training is performed progressively, following basic training principles.

High-intensity functional exercise in a group-setting is safe in high functioning adolescents with cerebral palsy (CP) when following basic training principles.Compound, multi-joint movements performed at high intensities show a transfer-effect into daily functionality.High-intensity resistance training combined with anaerobic and aerobic exercise should be included in standard therapy for high-functioning adolescents with CP.The group-setting shows potential as innovative strategy for long-term training effectiveness.

Prospective associations of physical fitness with spinal flexibility in childhood: implications for primary prevention of non-specific back pain.

Objectives: Early predictors for back pain need to be identified for the development of prevention strategies starting as early as childhood. For this purpose, the relationship between physical fitness and spinal flexibility at the age of six years and its prediction for the development of non-specific back pain (BP) during childhood were analyzed. Methods: In this prospective cohort study with 4-year follow-up, school children from the Swiss Canton Basel-Stadt, aged 6-8 (2014) at baseline and 10-12 years (2018) at follow-up, were recruited from 26 primary schools (n = 238) within a mandatory evaluation of motor skills. Data for spinal flexibility were collected by use of a hand-held computer-assisted device and physical fitness was assessed by shuttle run performance at both time points. Occurrence of non-specific BP was determined by use of a questionnaire at follow-up. Results: Children with higher physical fitness at baseline achieved a better spinal flexibility four years later (ß [95% CI] 3.75 [2.19-5.3] degree per 1 stage increase, p < 0.001). Higher spinal flexibility by 1 degree at baseline was associated with 2% less odds for non-specific BP at follow-up (OR [95% CI] 0.98 [0.97-0.99] per 1 degree increase, p = 0.032). There was little evidence for a direct association between physical fitness at baseline and development of non-specific BP at follow-up (OR [95% CI] 1.13 [0.96-1.34] per 1 stage increase, p = 0.128). Conclusion: Fitness performance is associated with the development of better childhood spinal flexibility over four years. Moreover, a better spinal flexibility at baseline was associated with less non-specific BP at follow-up. This study suggests that physical fitness may be a key modulator of spinal flexibility which itself is a main determinant of non-specific BP during childhood development. Further long-term studies are warranted to confirm our assumptions and to prove trajectories into adolescents and adulthood.