Biology subjects

Jakobi, J.

Publications and source records attributed to Jakobi, J..

3 recordsLinked to original sources

bioRxiv2026

Sex Differences in Motor Unit Properties and Force Steadiness: Insights from Strength-Matched Elbow Flexion

Sex-related differences in force steadiness are often attributed to maximal strength and motor unit (MU) properties, but their independent contributions remain unclear. This study strength-matched females and males to remove the influence of maximal strength and determine whether MU properties are associated with sex-related differences in force steadiness. Twelve young adults (6 females) were matched for elbow flexion strength (females, 188.6{+/-}15.6 N; males, 199.7{+/-}24.8 N, p=0.4). Both groups performed submaximal isometric elbow flexion contractions at 2.5%, 5%, 10%, 15%, and 25% MVC. The MU recruitment thresholds (RT), discharge rates (MUDR), and coefficient of variation of interspike intervals (CVISI) were measured from intramuscular fine wire electromyography (EMG) electrodes. Force steadiness was quantified as the standard deviation (SD) and coefficient of variation (CV) of force. Across forces, SD and CV of force did not differ between females and males (p>0.05). Females had a higher recruitment threshold than males (p<0.05). Females had higher MUDR at 15% and 25% MVC (p<0.02), while males were higher at 5% MVC (p=0.02). The CVISI was greater in females (p<0.001) and positively correlated with SD of force (r=0.2) and negatively with CV of force (r=-0.2) in females and males. When strength was matched, sex-related differences in force steadiness were not evident. However, females exhibited higher MU recruitment thresholds, MUDR and CVISI. Despite greater CVISI in females, these differences did not translate into greater force fluctuations, suggesting that individual MU discharge variability is not a primary predictor of force steadiness when maximal strength is controlled. NEW & NOTEWORTHYO_LIStrength matching eliminated sex-related differences in elbow flexor force steadiness. C_LIO_LIFemales achieved similar force steadiness using higher MU recruitment thresholds and discharge rates, particularly in the short head of the biceps brachii. C_LIO_LIIn females, the greater variability in motor unit discharge was not associated with reduced force steadiness. C_LI

physiology↗

bioRxiv2025

Value-Added: Importance of Incorporating Menstrual Cycle Phases to Clarify Sex-Related Differences in Force Steadiness

AimThis study aimed to determine whether female elbow flexion force steadiness varies across the menses, follicular and luteal phases of the menstrual cycle. MethodsTo control for repeated testing effects unrelated to hormonal fluctuations across the menstrual cycle, a comparison group of males completed the same protocol over three equally spaced testing sessions to the females. Maximal voluntary contractions and force steadiness were assessed in the neutral and pronated forearm positions. Elbow flexion force tracking tasks were performed at 2.5, 5, 10, 25, 50 and 75% maximal voluntary contraction in both forearm positions, and force steadiness was quantified as the coefficient of variation of force. ResultsMales were stronger than females (p<0.001), and maximal voluntary contractions did not differ between menstrual phases (p>0.14) or between days in males (p>0.56) in both forearm positions. There was no difference in coefficient of variation of force across sessions for the males (p<0.36). The coefficient of variation of force for all submaximal forces was significantly greater during the luteal phase compared to menses (Neutral p=0.02; Pronated p<0.05) but not the follicular phase (Neutral p=0.71; Pronated p=0.10). The coefficient of variation of force during the luteal phase in females was higher than males in both positions (p<0.02). ConclusionThese findings support previous observations that females are less steady than males for isometric steady contractions; however, this study identifies luteal specific phase effects. This underscores the importance of accounting for menstrual cycle phase when conducting sex-related comparisons.

physiology↗

bioRxiv2024

Plk1 inhibition delays mitotic entry revealing prophase-specific changes to the phosphoproteome

Polo-like kinase 1 (plk1) is a conserved regulator of cell division. During prophase, plk1 phosphorylates direct substrates and is involved in activation of the cyclin-dependent kinase 1 (cdk1). However, the exact functions of plk1 in prophase remain incompletely understood. By testing several cell lines and small-molecule inhibitors, we confirm that plk1 inhibition causes a delay in mitotic entry. We show that cells are delayed in a prophase-like state displaying progressively condensing chromosomes, increased microtubule dynamics, reorganization of the actin cortex, while the nuclear envelope remains intact. We show that during this prolonged prophase cdk1 activity increases gradually over several hours with individual cells stochastically reaching the entry threshold, explaining the highly variable timing of mitotic entry. We then use phosphoproteomics to characterize this prolonged prophase state revealing for the first time phosphosites specific to prophase including several regulators of chromatin organization and the cytoskeleton. Together, we show that plk1 functions as a catalyst of prophase to prometaphase transition, and by using plk1 inhibition as a tool, we identify early changes in the phosphoproteome as the cell prepares for division.

cell biology↗