Mathias Vedsø Kristiansen

Inter-subject variability of muscle synergies during bench press in power lifters and untrained individuals

The purpose of the study was to elucidate the role of expertise on muscle synergies involved in bench press. Ten expert power lifters (EXP) and nine untrained participants (UNT) completed three sets of eight repetitions at 60% of three repetition maximum in bench press. Muscle synergies were extracted from surface electromyography data of 21 bench press cycles using non‐negative matrix factorization algorithm. The synergy activation coefficient represents the relative contribution of the muscle synergy to the overall muscle activity pattern, while the muscle synergy vector represents the relative weighting of each muscle within each synergy. Describing more than 90% of the variability, two muscle synergies reflected the eccentric and concentric phase. The cross‐correlations (ρmax) for synergy activation coefficient 2 (concentric phase) were 0.83 [0.71;0.88] and 0.59 [0.49;0.77] [Median ρmax (25th;75th percentile)] (P = 0.001) in UNT and EXP, respectively. Median correlation coefficient (ρ) for muscle synergy vector 2 was 0.15 [−0.08;0.46] and 0.48 [0.02;0.70] (P = 0.03) in UNT and EXP, respectively. Thus, EXP showed larger inter‐subject variability than UNT in the synergy activation coefficient during the concentric phase, while the muscle synergy vectors were less variable in EXP. This points at the importance of a specialized neural strategy in elite bench press performance.

Effects of 5 weeks of bench press training on muscle synergies: a randomized controlled study

Abstract Kristiansen, M, Samani, A, Madeleine, P, and Hansen, EA. Effects of 5 weeks of bench press training on muscle synergies: A randomized controlled study. J Strength Cond Res 30(7): 1948–1959, 2016—The ability to perform forceful muscle contractions has important implications in sports performance and in activities of daily living. However, there is a lack of knowledge on adaptations in intermuscular coordination after strength training. The purpose of this study was therefore to assess muscle synergies before and after 5 weeks of bench press training. Thirty untrained male subjects were randomly allocated to a training group (TRA) or a control group (CON). After the pretest, TRA completed 5 weeks of bench press training, before completing a posttest, whereas subjects in CON continued their normal life. During test sessions, surface electromyography (EMG) was recorded from 13 different muscles. Muscle synergies were extracted from EMG data using nonnegative matrix factorization. To evaluate differences between pretest and posttest, we performed a cross-correlation analysis and a cross-validation analysis, in which the synergy components extracted in the pretest session were recomputed, using the fixed synergy components from the posttest session. Two muscle synergies accounted for >90% of the total variance and reflected the concentric and eccentric phase, respectively. TRA significantly increased 3 repetition maximum in bench press with 19.0% (25th; 75th percentile, 10.3%; 21.7%) (p < 0.001), whereas no change occurred in CON. No significant differences were observed in synergy components between groups. However, decreases in correlation values for intragroup comparisons in TRA may suggest that the synergy components changed, whereas this was not the case in CON. Strength and conditioning professionals may consider monitoring changes in muscle synergies in training and rehabilitation programs as a way to benchmark changes in intermuscular coordination.

Muscle synergies during bench press are reliable across days

Muscle synergies have been investigated during different types of human movement using nonnegative matrix factorization. However, there are not any reports available on the reliability of the method. To evaluate between-day reliability, 21 subjects performed bench press, in two test sessions separated by approximately 7days. The movement consisted of 3 sets of 8 repetitions at 60% of the three repetition maximum in bench press. Muscle synergies were extracted from electromyography data of 13 muscles, using nonnegative matrix factorization. To evaluate between-day reliability, we performed a cross-correlation analysis and a cross-validation analysis, in which the synergy components extracted in the first test session were recomputed, using the fixed synergy components from the second test session. Two muscle synergies accounted for >90% of the total variance, and reflected the concentric and eccentric phase, respectively. The cross-correlation values were strong to very strong (r-values between 0.58 and 0.89), while the cross-validation values ranged from substantial to almost perfect (ICC3, 1 values between 0.70 and 0.95). The present findings revealed that the same general structure of the muscle synergies was present across days and the extraction of muscle synergies is thus deemed reliable.

Inter- and Intrasubject Similarity of Muscle Synergies During Bench Press With Slow and Fast Velocity

We investigated the effect of low and high bar velocity on inter- and intrasubject similarity of muscle synergies during bench press. A total of 13 trained male subjects underwent two exercise conditions: a slow- and a fast-velocity bench press. Surface electromyography was recorded from 13 muscles, and muscle synergies were extracted using a nonnegative matrix factorization algorithm. The intrasubject similarity across conditions and intersubject similarity within conditions were computed for muscle synergy vectors and activation coefficients. Two muscle synergies were sufficient to describe the dataset variability. For the second synergy activation coefficient, the intersubject similarity within the fast-velocity condition was greater than the intrasubject similarity of the activation coefficient across the conditions. An opposite pattern was observed for the first muscle synergy vector. We concluded that the activation coefficients are robust within conditions, indicating a robust temporal pattern of muscular activity across individuals, but the muscle synergy vector seemed to be individually assigned.

Muscle synergies during bench press

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Ergonomics in sports and at work

This paper addresses issues related to ergonomics in sports and at work. Ergonomics and sports science disciplines are interrelated. Workers and athletes operate in demanding environments requiring a high level of performance. Thus, a branch of ergonomics focuses on quantifying motor strategies in order to optimize human performance and prevent injuries. These goals can be pursued by (i) assessing human characteristics and capabilities in relation to certain motor tasks, (ii) achieving optimal efficiency and improving the overall level of performance, (iii) reducing discomfort level, and (iv) ensuring safety. This paper reviews recent studies and presents novel methods used to assess human performance.