Effects of Adding End-Range Isometric Holds to Isotonic Knee Extensor Training on Isokinetic Performance in Sedentary Adults

Effects of Adding End-Range Isometric Holds to Isotonic Knee Extensor Training on Isokinetic Performance in Sedentary Adults: A Randomized Controlled Trial

The goal of this clinical trial is to learn if adding a short muscle hold (isometric contraction) to a standard leg-strengthening exercise improves knee muscle strength more than the standard exercise alone, in healthy adults who do not exercise regularly. The main question it aims to answer is:

Does adding a 5-second hold at the end of each leg-extension exercise lead to greater gains in front-thigh muscle (quadriceps) strength than leg-extension exercise alone?

Researchers will compare two exercise groups to see if the added muscle hold makes a difference:

Group 1 will do leg-extension exercises with a 5-second hold added at the end of each repetition.

Group 2 will do the same leg-extension exercises without the added hold.

Participants will:

Do leg-extension exercises 3 days a week for 8 weeks Have their thigh muscle strength tested before and after the program using a special exercise machine Have their thigh size measured before and after the program

Study Overview

• Status: Completed
• Conditions: Quadriceps Muscle Strength; Isokinetic
• Intervention / Treatment: Other: Isotonic Exercise With Added Isometric Hold; Other: Isotonic Exercise Only

Detailed Description

Quadriceps femoris weakness is associated with several musculoskeletal conditions, including knee osteoarthritis, and is a common target of physiotherapy strengthening protocols. While isotonic and isokinetic strengthening methods have each been studied separately, it remains unclear whether adding an isometric hold to isotonic exercise provides additional benefit in isokinetic strength outcomes. This study addressed that question.

This was a randomized, two-arm study conducted at the Sportomed Sports Health and Orthopedic Rehabilitation Clinic (December 2014-May 2015). Forty-six sedentary, healthy adults aged 18-40 years were enrolled, with 43 completing the 8-week protocol. Exclusion criteria included lower-extremity musculoskeletal problems, prior lower-extremity surgery or significant trauma, low back pain, cardiac or neurological conditions, and chronic systemic disease. The study was approved by the Istanbul Medipol University Non-Interventional Clinical Research Ethics Committee (decision no. 257, 07.11.2014), and written informed consent was obtained from all participants.

Participants were randomized to two groups. Both performed isotonic knee-extension exercise (2 sets × 10 repetitions, 60% of 1RM) 3 days/week for 8 weeks, with weekly load progression (~5%) and 60 seconds rest between sets. Group 1 (n=21) added a 5-second isometric hold at 0° knee extension at the end of each repetition; Group 2 (n=22) performed the isotonic protocol without this addition.

Outcomes were assessed at baseline and after 8 weeks: thigh circumference, 1RM isotonic quadriceps strength, and isokinetic peak torque (PT, Nm) at 60°/second and 180°/second using a CSMI Humac Norm 2004 dynamometer. Baseline assessments also included range of motion, manual muscle testing, and physical activity level (IPAQ Short Form).

Statistical analysis was performed using NCSS 2007. Normality was assessed with Shapiro-Wilk testing. Between-group comparisons used independent t-tests or Mann-Whitney U tests as appropriate; within-group pre-post comparisons used paired t-tests. Categorical variables were compared using chi-square testing, and correlations using Pearson testing. Significance was set at p<0.05.

• Study Type: Interventional
• Enrollment (Actual): 43
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Bostancı/Kadıköy
    • Istanbul, Bostancı/Kadıköy, Turkey (Türkiye), 34744
      • Sportomed | Physical Therapy and Rehabilitation Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Age 18-40 years
• Sedentary lifestyle (low physical activity level)
• Healthy individuals with no known knee-related disability

Exclusion Criteria:

• Musculoskeletal problems of the lower extremity
• History of lower extremity surgery or significant trauma
• Low back pain and/or lumbar region problems
• Cardiac complaints
• Neurological complaints
• Chronic systemic disease (e.g., diabetes mellitus, rheumatologic conditions)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Isotonic + Isometric Hold Group; Participants performed isotonic knee-extension exercise (2 sets of 10 repetitions at 60% of 1-repetition maximum) using a leg-extension machine, 3 days per week for 8 weeks, with weekly load progression (~5%) and 60 seconds of rest between sets. At the end of each repetition, participants held the lifted weight for 5 seconds at 0° knee extension (isometric contraction) before returning to the starting position.	Other: Isotonic Exercise With Added Isometric Hold; Isotonic knee-extension exercise (2 sets of 10 repetitions at 60% of 1-repetition maximum) performed 3 days per week for 8 weeks, with weekly load progression (~5%) and 60 seconds of rest between sets. Each repetition concluded with a 5-second isometric hold of the lifted weight at 0° knee extension.
Active Comparator: Isotonic Only Group; Participants performed the same isotonic knee-extension exercise protocol (2 sets of 10 repetitions at 60% of 1-repetition maximum) using a leg-extension machine, 3 days per week for 8 weeks, with weekly load progression (~5%) and 60 seconds of rest between sets, without the addition of an isometric hold at the end of each repetition.	Other: Isotonic Exercise Only; Isotonic knee-extension exercise (2 sets of 10 repetitions at 60% of 1-repetition maximum) performed 3 days per week for 8 weeks, with weekly load progression (~5%) and 60 seconds of rest between sets, without an added isometric hold.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Quadriceps Femoris Isokinetic Peak Torque	Quadriceps femoris isokinetic peak torque (PT, Nm) was measured bilaterally using a CSMI Humac Norm 2004 isokinetic dynamometer at angular velocities of 60°/second (5 maximal repetitions) and 180°/second (15 maximal repetitions).	Baseline and 8 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Quadriceps Femoris 1-Repetition Maximum (1RM) Isotonic Strength	Quadriceps femoris 1-repetition maximum isotonic strength was measured bilaterally using a leg-extension apparatus, with each disk increment corresponding to 10 lbs (4.54 kg).	Baseline and 8 weeks
Change in Thigh Circumference	Thigh circumference was measured bilaterally, 15 cm proximal to the superior border of the patella, using a measuring tape, in the supine position.	Baseline and 8 weeks

Collaborators and Investigators

• Sponsor: Yeditepe University
• Investigators: Study Director: Feyza Şule Hantal, PhD, Yeditepe University

Study record dates

Study Major Dates

• Study Start (Actual): December 12, 2014
• Primary Completion (Actual): May 26, 2015
• Study Completion (Actual): July 6, 2015

Study Registration Dates

• First Submitted: June 19, 2026
• First Submitted That Met QC Criteria: June 24, 2026
• First Posted (Actual): June 25, 2026

Study Record Updates

• Last Update Posted (Actual): June 30, 2026
• Last Update Submitted That Met QC Criteria: June 25, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: resistance training; isometric contraction; quadriceps muscle; knee extensor strength; isokinetic exercise
• Other Study ID Numbers: 127742

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No