# The effects, mechanisms, and influencing factors of concurrent strength and endurance training with different sequences: a semi-systematic review

## TL;DR

This review explores how the order of strength and endurance training affects performance, focusing on neuromuscular and molecular changes.

## Contribution

The study provides insights into how training sequence influences neuromuscular adaptations and highlights species differences in molecular responses.

## Key findings

- A 'strength-first' sequence optimizes neuromuscular adaptations and enhances relative strength and explosive power.
- Acute molecular responses vary with training sequence, but long-term adaptations are complex and non-linear.
- Animal studies show stronger regulatory effects of training sequence on hypertrophy-related pathways compared to human studies.

## Abstract

Objective: This study investigated how the sequencing of strength and endurance training affects athletic performance, and delved into the underlying mechanisms from the perspectives of neuromuscular and molecular adaptations. Furthermore, factors influencing the effectiveness of concurrent training with different sequences were also analyzed. Design and Methods: A semi-systematic review was conducted following the PRISMA guidelines. Relevant literature was retrieved from PubMed, Web of Science, EBSCO, and CNKI databases using the search terms: “concurrent training”, “simultaneous training”, “combined training”, “concurrent strength and endurance training”, “simultaneous strength and endurance training”, “combined strength and endurance training”, “sequence”, “order”. The retrieval timeframe was from January 1980 to December 2024. Results: Analysis of the 42 included studies revealed that, in human trials, while training sequence generally shows no consistent association with the ultimate gains in endurance, muscle hypertrophy, or maximal strength, adopting a “strength-first” modality optimizes neuromuscular adaptations, thereby enhancing relative strength and explosive power. Although acute molecular responses (e.g., mTOR/AMPK phosphorylation) exhibit sequence-dependent variations, their translation into long-term adaptations is complex and non-linear. Notably, animal experiments demonstrate a far more pronounced regulatory effect of training sequence on hypertrophy-related pathways than human studies, suggesting that species differences and training methodologies may be key contributing factors. Recommendations: The training sequence should be arranged reasonably based on the training objectives and the individual differences among the subjects (e.g., age, training status, sport modality). If the endurance-strength training mode is chosen, it is recommended that the interval between the two types of training be more than 3 h to prevent acute molecular interference. For athletes targeting explosive power or relative strength, the strength-endurance sequence is preferred.