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

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.

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)