ISOMETRIC TRAINING AND LONG-TERM ADAPTATIONS: EFFECTS OF MUSCLE LENGTH, INTENSITY, AND INTENT: A SYSTEMATIC REVIEW

BACKGROUND & OBJECTIVE

Isometric exercise has a wide range of uses from pain reduction and loading injured tissue to building muscular strength and improving tendon resilience. It is applied across nearly all populations with utility for high level athletes, specialized populations, and the general public as well. The purpose of this review was to examine medium to long term adaptations of isometric training on morphological, neurological and performance variables while providing evidence-based training guidelines for a variety of desired outcomes.

METHODS

The authors used a PRISMA system to gather and assess relevant articles for the systematic review. PRISMA is an acronym standing for preferred reporting items for systematic reviews and meta-analyses. Studies were only included if they were found in peer-reviewed journals, compared two or more variations of isometric exercise, and had an intervention period of at least three weeks. Studies were excluded if any of the interventions included the use of modalities (e.g. blood flow restriction training or electrical stimulation).

26 studies were included with a total of 713 participants (463 male, 250 female). The majority of the studies (16/26) recruited untrained participants, while the remainder utilized “active” or “recreationally trained” participants. Ten studies included a control group. The mean length of intervention was approximately 8 weeks with an average of 3.5 sessions per week. The authors sought to compare variables of intensity, frequency, duration, contraction intent, and joint angle in order to better understand how to apply isometric exercise with maximal efficiency and correspondence towards the training or rehabilitation goal.

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RESULTS

Isometric exercise appears to respond to specificity of training very similarly to dynamic exercise. Longer time under tension and metabolic stress leads to greater hypertrophic adaptations, whereas shorter time under tension and greater contraction intent or speed leads to more

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