Hormonal fluctuations throughout the menstrual cycle are associated with a higher prevalence of musculoskeletal injuries in women; however, their impact at the foot and ankle level remains underexplored. The aim of this systematic review and meta-analysis was to examine the potential biomechanical effect of the ovulatory phase on foot and ankle structure compared to other phases of the menstrual cycle, given its possible association with injury occurrence. A systematic search was conducted in PubMed, Scopus, Web Of Science, and Embase (last 10 years), following PRISMA guidelines. Cohort studies, non-randomized trials, and case-control studies were included. Quality assessment was performed using the JBI critical appraisal tool. A quantitative synthesis (meta-analysis) was performed for homogeneous variables (muscle stiffness). Fifteen studies were selected. The systematic review demonstrated increase in foot length, reduction in fascial thickness, and greater longitudinal arch collapse during the ovulatory phase. Tone and stiffness of the tibialis anterior and peroneus longus muscles were greater during the menstrual phase. During ovulation, lower stiffness was observed during active contraction and increased tibialis anterior activation. Greater postural sway and oscillation were recorded during ovulation in complex static tasks, and, along with the menstrual phase, in dynamic balance tests. The meta-analysis indicated a tendency towards lower tibialis anterior stiffness during the follicular phase compared to the ovulatory phase. The ovulatory phase appears to be associated with an interaction of structural alterations (ligament laxity and arch collapse) and neuromuscular changes (reduced muscle stiffness and inefficient motor control) that, together, could constitute a risk factor for local pathologies such as plantar fasciitis and chronic ankle instability.

Anterior cruciate ligament reconstruction using peroneus longus with lateral extra-articular tenodesis has excellent functional outcomes with a high return to sport rate: A prospective cohort study of 482 patients over 2years.

Plantarflexion of the first ray is an important component of cavovarus foot deformities, which is thought to be due to the pull of the peroneus longus muscle. We inferred its action by studying its insertion into the peroneus longus tubercle (PLT). Our aim was to determine how PLT orientation and morphology differs in cavovarus feet compared to controls on weightbearing computed tomography (WBCT) imaging. We retrospectively analysed 30 WBCT scans from patients with cavovarus feet and Charcot-Marie Tooth disease. We compared these to 30 normal feet using previously described measurements of PLT morphology: tubercle-to-floor (T-F) distance; bisecting angle and tubercle-to-metatarsal (T-MT) angle. The intraclass correlation coefficient (ICC) was used to assess reliability. Individuals with cavovarus feet were found to have a higher T-F distance by an average of 9.63 mm (p < 0.001), a greater vertical bisecting angle (> 10 °, p = 0.002) and a lower T-MT angle (<11 °, p < 0.001). This suggests net forefoot supination with relative pronation of the first ray. Intra- and Inter-observer reliability was excellent. We observed the PLT is both greater in size and more vertically oriented in cavovarus feet, with relative pronation of the PLT orientation when compared to the rest of the forefoot. The height of the PLT from the floor is also greater. Overall, this likely infers that the action of peroneus longus in cavovarus feet is to plantarflex and pronate the first ray, relative to a supinated forefoot. III.

One repetition maximum (1RM) testing is recognised as a reliable and valid method for determining maximum muscle strength. However, there are limited reports in the literature for measuring maximum ankle strength using free-weight methods. The aim of this study was to determine the test-retest reliability and concurrent validity of a novel free-weight device (ISOTIB) used to measure ankle strength. Fifteen healthy, recreationally active, adults (male=10, female=5, age=29.7±4.4years) volunteered for the study, attending two sessions 1week apart. Reliability was assessed using intraclass correlation coefficients (ICC(3,1)) and Bland-Altman method. Concurrent validity was examined by comparing 1RM ankle strength and normalised muscle activity using surface electromyography (sEMG) during dorsiflexion, inversion, and eversion movements performed with the ISOTIB device and an isokinetic dynamometer. The ISOTIB exhibited excellent test-retest reliability for maximal dorsiflexion (ICC(3,1)=0.99, 95% CI: 0.977-0.997), inversion (ICC(3,1)=0.99, 95% CI: 0.970-0.997), and eversion (ICC(3,1)=0.97, 95% CI: 0.920-0.991) strength. Concurrent validity was confirmed, with high positive correlations for maximal dorsiflexion (r=0.90, 95% CI: 0.72-0.97) p<0.001), inversion (r=0.67, 95% CI: 0.24-0.88) p<0.007), and eversion (r=0.87, 95% CI: 0.64-0.96) p<0.001) strength. sEMG results supported concurrent validity with comparable activity in the tibialis anterior, peroneus longus, and peroneus brevis muscles. The ISOTIB demonstrated excellent reliability and validity, suggesting it is a viable tool for assessing maximal ankle strength. The ISOTIB offers a practical alternative to current methods, which are typically expensive and utilise large immovable devices.

Intramedullary fibular nailing (IFN) offers a minimally invasive alternative to plate fixation for unstable ankle fractures, yet concerns persist regarding potential iatrogenic injury to the peroneal tendons during portal creation. No previousin vivo study has evaluated tendon integrity after IFN using advanced imaging. In this cohort, we examined peroneal tendon morphology and syndesmotic reduction following IFN using serial postoperative magnetic resonance imaging (MRI), comparing findings with a healthy control group. A prospective cohort of 102 adults with unstable Weber B or C ankle fractures underwent IFN and completed at least eight months of follow-up. All patients received standardized ankle MRI at 3 and 8 months postoperatively. Tendon morphology, signal characteristics, and thickness were assessed by a blinded musculoskeletal radiologist. Syndesmotic reduction was evaluated in patients requiring trans-syndesmotic fixation. A control group of ten healthy volunteers underwent the same MRI protocol. Statistical comparisons were performed using independent-samples t tests and equivalence testing with predefined margins. Peroneal tendons demonstrated no MRI-detectable pathology at both 3 and 8 months. At 8 months, tendon thickness (peroneal brevis: 2.9 ± 0.3mm; peroneal longus: 3.4 ± 0.4mm) was comparable to controls (2.8 ± 0.3mm and 3.4 ± 0.4mm; p>0.37), meeting equivalence criteria (TOST p<0.001). Among patients requiring syndesmotic fixation (n=28), tibiofibular alignment remained anatomic (clear space: 3.1 ± 0.4mm; overlap: 8.7 ± 1.2mm). Union was achieved in all cases, with no infections or tendon-related symptoms. Intramedullary fibular nailing preserves peroneal tendon integrity and provides reliable syndesmotic stability when performed with proper technique. Tendon morphology and signals remained indistinguishable from healthy controls, and postoperative alignment was consistently anatomic. These findings support IFN as a safe, biologically respectful option for the treatment of unstable ankle fractures.

Mid-term functional outcomes of arthroscopy-assisted lower trapezius transfer using doubled peroneus longus tendon.

Differential effects of standing widths and foot abduction angles on muscle synergy during squatting in adult males.

Biomechanical comparison of tendon graft suturing techniques in arthroscopic ligament reconstruction using a novel knotless method in a cadaveric model.

This study evaluated the maturation of the peroneus longus (PL) tendon autograft by quantifying the key diffusion tensor imaging (DTI) parameters: fractional anisotropy (FA) and apparent diffusion coefficient (ADC) at 1 year of follow-up in patients undergoing all-inside anterior cruciate ligament (ACL) reconstruction surgery. Magnetic resonance imaging (MRI) of the knee with DTI sequences was done at 1 year of follow-up for 50 patients (mean age 26.6 ± 8.5 years; 41 males + 9 females), who underwent ACL reconstruction using PL tendon autograft. FA and ADC at different parts of the graft (femoral, mid-substance and tibial) were determined with regions of interest (ROI)-based measurements after assessing the fibre morphology on the proton density fat-saturated (PDFS) images. Figueroa scores using the conventional MRI sequences were also calculated at 1 year of follow-up and compared with the DTI parameters. The Tegner-Lysholm and knee society scores were used to evaluate functional outcomes. At 1 year, mean FA and ADC values were 0.2 ± 0.1 and 1.7 ± 0.1 × 10-3 mm²/s, both different from the reported values for native ACL. The majority of patients (35/50) had a Figueroa score of 4, indicating adequate but incomplete graft maturation. The FA and ADC values of the three individual regions of the graft, as well as the overall mean value, did not show any significant difference between the three Figueroa score groups (Figueroa score 3 vs. 4 vs. 5). There was a significant improvement (p < 0.001) in the patient-reported outcome measures at the final follow-up. DTI and conventional MRI parameters showed substantial but incomplete graft maturation, despite excellent functional recovery, at 1 year of follow-up. Our study supports the use of PL tendon as a reliable graft option, demonstrating acceptable graft maturation and favourable functional outcomes. Advanced imaging may assist in individualised return-to-sport decision-making. Level II.

Hallux valgus (HV) is associated with altered activation of intrinsic and extrinsic foot muscles, which may be relevant to rehabilitation planning. Understanding task-specific muscle activation during commonly prescribed exercises may help inform exercise selection. This study aimed to compare the electromyographic activity of the abductor hallucis (ABH), peroneus longus (PL), flexor hallucis longus (FHL), and extensor hallucis longus (EHL) muscles during nine foot exercises in women with HV. Seventeen women with moderate-to-severe hallux valgus (22.2 ± 3.1 years) performed nine exercises: sitting short-foot, standing short-foot, single-leg short-foot, towel curl, toe-spread-out, three-dimensional foot-ankle extension in diagonals 1 and 2 (3DFA-D1E and 3DFA-D2E) patterns, calf raise, and stand swing. Surface electromyography signals were recorded from the ABH, PL, FHL, and EHL muscles. The signals were processed using a 150-ms moving root mean square (RMS) window. The mean RMS amplitude calculated from the middle three seconds of the 5-s sustained contraction phase was used for analysis. Significant differences in EMG amplitude were observed across exercises for all evaluated muscles (p < 0.001). ABH showed relatively lower activation during towel curl (p < 0.05), and higher activation during single-leg short-foot, toe-spread-out, and stand swing (p < 0.05). PL activation was highest during calf raise and 3DFA-D1E. FHL activation was highest during towel curl, 3DFA-D1E and 3DFA-D2E (p < 0.01), and calf raise, whereas sitting short-foot and toe-spread-out elicited relatively low FHL activation (p < 0.01). EHL showed highest activation during single-leg short-foot and toe-spread-out than during several other exercises (p < 0.05). These findings provide preliminary information on task-specific muscle activation patterns during commonly prescribed foot exercises in women with HV. Exercises such as single-leg short-foot, toe-spread-out, calf raise, stand swing, and 3DFA extension may help inform muscle-targeted exercise selection in HV rehabilitation; however, the long-term clinical effects of these exercises require confirmation in longitudinal and interventional studies.

Chronic ankle instability (CAI) is a prevalent sequela of lateral ankle sprains, primarily characterized by impaired neuromuscular control. Although tissue flossing (TF) has demonstrated potential in acutely enhancing neuromuscular function in CAI patients, its long-term rehabilitative effects remain unclear. This study aimed to investigate the long-term neuromuscular adaptive effects of combining TF with balance training in CAI patients. Thirty-four participants with CAI were randomly assigned (using a random number remainder method) to an 8-week intervention of either balance training combined with TF (FLOSS group, n = 17) or balance training alone (CON group, n = 17).Outcome measures, assessed pre- and post-intervention, included muscle reaction time and activation level of the tibialis anterior (TA) and peroneus longus (PL) measured using surface electromyography, isometric strength was measured with a hand-held dynamometer, static balance was evaluated via a unilateral stance test (UST) on a balance system, and dynamic balance was assessed using the Y-Balance Test (YBT). Data were analyzed using a 2 (time: pre vs. post) × 2 (group: FLOSS vs. CON) repeated-measures analysis of variance. Following the intervention, a significant Time × Group interaction was found only for the RMS amplitude of the TA during the anterior reach task (F (1, 28) = 4.417, p = 0.044, ηp2 = 0.121, large effect size), with no significant between-group difference in post-hoc tests (p = 0.454). Muscle reaction time and static balance improved significantly from baseline in all participants, but the magnitude of improvement did not differ between groups. No additional between-group differences were observed in ankle muscle strength, dynamic balance, or electromyographic activity in other directions. TF combined with balance training did not provide statistically significant additional long-term benefits compared to balance training alone.Clinical trial registration: This trial was registered at the Chinese Clinical Trial Registry (Identifier: ChiCTR2400092294) (https://www.chictr.org.cn/bin/userProject?status=%E9%80%9A%E8%BF%87%E5%AE%A1%E6%A0%B8).

To evaluate the predictive value of magnetic resonance imaging (MRI)-derived cross-sectional area (CSA) measurements of hamstring and peroneus longus tendons in estimating intraoperative autograft diameter during anterior cruciate ligament (ACL) reconstruction, and to identify clinically useful CSA cut-offs for achieving graft diameters ≥ 8mm. Fifty-two patients undergoing primary ACL reconstruction were included in this prospective observational study, with 26 each in the hamstring tendon (HT) and peroneus longus tendon (PLT) autograft groups. Preoperative CSA was measured on axial MRI at specific anatomical levels. Intraoperative graft diameters were recorded post- harvest. Correlation analysis and receiver operating characteristic curves were used to assess predictive value and determine CSA thresholds for adequate graft size. For the HT group, CSA measured at the medial femoral condyle showed the strongest correlation with intraoperative diameter (r = 0.782; p < 0.001), with an optimal CSA cut-off of ≥ 19.15mm² (AUC 0.917, sensitivity: 85%, specificity: 100%). For the PLT group, ankle-level CSA best predicted graft diameter (cut-off: ≥12.84mm², AUC 0.958, sensitivity: 95.8%, specificity: 100%). MRI-based CSA measurement provides a reliable, non-invasive method for predicting autograft adequacy. This study establishes clinically relevant CSA thresholds for HT and PLT tendons and is the first to report such values for PLT, aiding preoperative graft selection in ACL reconstruction.

Prediction of ankle kinematics and kinetics in stair ascent motion using surface EMG feature inputs of lower extremity muscle combinations.

Assessing isometric ankle abductor strength with a novel device: Reliability and electromyographic validation.

Introduction:Anterior cruciate ligament (ACL) injury remains one of the most common causes of functional knee instability among young and active individuals. Autografts, especially hamstring tendon (HT) grafts, have long been considered the standard of care; however, concerns regarding variable graft diameter, harvest-related muscle weakness, and donor-site morbidity have led to interest in alternative grafts. The peroneus longus tendon (PLT) has gained attention due to its adequate length, favorable biomechanical strength, and minimal functional deficit at the donor site. This randomized controlled trial compared the clinical, functional, and stability outcomes of PLT autografts with HT autografts in primary ACL reconstruction.Materials and Methods:A prospective randomized controlled trial was conducted on 50 patients undergoing primary ACL reconstruction. Participants were randomized into two equal groups: Group A received PLT autograft (n = 25), and Group B received HT autograft (n = 25). Baseline characteristics, intraoperative parameters, post-operative pain, knee stability, donor-site morbidity, and functional outcomes were assessed using International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores at 3 and 6 months. KT-1000 arthrometer measurements, Lachman and pivot-shift tests were used for objective stability assessment. Data were analyzed using the Statistical Package for the Social Sciences, with P < 0.05 considered statistically significant.Results:Baseline demographic variables were comparable between groups. PLT grafts demonstrated significantly larger mean graft diameter (8.9 ± 0.6 mm) compared to HT grafts (8.1 ± 0.7 mm; P = 0.001). Operative time was significantly shorter in the PLT group (78.6 ± 11.3 min vs. 86.2 ± 12.7 min; P = 0.02). Early post-operative pain scores were lower in the PLT group (P < 0.05). At 6 months, the PLT group showed significantly higher IKDC (82.6 ± 6.3 vs. 78.9 ± 7.4; P = 0.04) and Lysholm scores (89.4 ± 5.8 vs. 85.1 ± 6.4; P = 0.03). Knee stability outcomes, including Lachman grade, pivot shift, and KT-1000 measurements, were comparable across groups. Donor-site morbidity was significantly lower in the PLT group, with minimal ankle strength deficit compared to notable hamstring weakness in the HT group. Complication rates were low and similar across both groups.Conclusion:PLT autograft demonstrated larger graft diameter, reduced post-operative pain, better early functional outcomes, and lower donor-site morbidity compared with the traditional hamstring autograft while maintaining equivalent knee stability. PLT appears to be a reliable and effective graft option for primary ACL reconstruction, especially in individuals where preservation of hamstring strength is desirable.

Introduction:Although uncommon, chronic patellar tendon rupture and failure of primary repair can be challenging to treat and compromise the knee extensor mechanism. When tendon quality is poor and there is quadriceps contracture or fibrosis, repair may be limited, making patellar tendon reconstruction the preferred treatment approach. However, no unified view exists on the optimal graft selection for reconstruction of the patellar tendon.Case Series:This is a case series of five patients treated in a tertiary care facility between 2022 and 2025 for chronic or failed primary patellar tendon ruptures. In all five patients, reconstruction was performed using the ipsilateral hamstring or peroneal autografts. The harvested tendon was passed in a figure-of-eight fashion through trans-osseous tunnels created on the patella and the tibial tuberosity. The graft was then fixed to the tibia with bioabsorbable screws and suture anchors. Functional outcomes were evaluated at the final follow-up of 6 months, focusing on the range of motion, extensor lag, radiographic patellar height, and complications observed post-surgery.Results:At final follow-up, four out of five patients gained full active knee extension without any extensor lag, while one patient still had an extension lag of 20°. The range of knee flexion was 100–130°. No cases of re-rupture or fixation failure were observed. There was minimal donor-site morbidity, and no significant ankle instability was noted in patients who underwent peroneus longus tendon harvest.Conclusion:Patellar tendon reconstruction using autografts provides reliable restoration of knee extensor function in chronic ruptures and failed primary repairs. Both hamstring and peroneus longus tendons are effective graft options, and graft selection should be individualized based on tendon defect size, tissue quality, and intraoperative findings. Accurate restoration of patellar height is critical for optimal functional outcomes.

HighlightsWhat are the main findings?Threshold-level plantar white-noise vibration combined with multi-site plantar stimulation may help improve postural control in healthy young adults.The intervention showed no marked change in ankle muscle activation, suggesting that the observed balance-related effects may be associated with sensory modulation rather than direct motor enhancement.What are the implications of the main findings?The 8-week plantar vibration intervention was associated with a reduction in the center-of-pressure envelope area during single-leg stance, suggesting a potential sustained effect on balance performance.These findings may provide a basis for further optimizing plantar vibration protocols for balance rehabilitation and injury prevention.Postural control is essential for daily function, and while stochastic resonance (SR) enhances balance in clinical populations, its efficacy in healthy young people remains underexplored. This study investigated (1) biomechanical effects of multisite plantar vibration on postural stability using center-of-pressure (CoP) parameters, and (2) short-term and sustained effects on balance performances. Phase 1 enrolled six participants to identify the optimal plantar stimulation configuration and to evaluate acute electromyographic responses under threshold-level vibration. Phase 2 evaluated long-term efficacy through an eight-week sham-controlled parallel-group randomized controlled trial. In this trial, eight participants received vibration combined with balance training, and another eight participants completed the same training protocol using sham insoles without vibration, analyzing CoP parameters (95% ellipse area, path length) and muscle activation (tibialis anterior, medial gastrocnemius, peroneus longus, extensor digitorum longus). Results showed full-site vibration reduced CoP area versus control (265.66 ± 188.6 mm2 vs. 437.84 ± 190.95 mm2, p < 0.05) without altering ankle muscle activation (all p > 0.05). Longitudinal analysis revealed CoP area reduction (−4.88 ± 10.42%) in the intervention group versus sham (p < 0.001), with maximum anterior displacement increasing by 25.03% during vibration (p < 0.05). Plantar white-noise vibration modulates CoP oscillations without neuromuscular activation changes, demonstrating that full-site stimulation acutely enhances postural stability while sustained intervention improves dynamic balance control.

Background Peroneal tendon disorders, encompassing tendinopathy, tears, subluxation, and instability, represent a significant source of lateral ankle pain and functional impairment, often exacerbated by underlying conditions such as cavovarus foot deformities or chronic lateral ankle instability. In cases of severe peroneus brevis degeneration or irreparable tears, peroneal longus to brevis tendon transfer is an effective technique to restore eversion strength and dynamic stability, though challenges persist in patients with poor tissue quality necessitating augmentation. Purpose To present a novel case of peroneus longus-to-brevis transfer augmented with the TeKBrace synthetic graft for complex peroneal pathology. Case Presentation. A 31-year-old man presented with persistent lateral ankle pain following an inversion injury 6 months prior. Conservative management, including an orthopaedic boot, home exercises, nonsteroidal anti-inflammatory drugs, physical therapy, and a peroneal tendon steroid injection, provided limited relief. Physical examination revealed cavus foot posture, tenderness over the peroneal tendons and lateral ligaments and pain with eversion. Magnetic resonance imaging showed tears in both peroneal tendons and increased signal at the peroneal tubercle. Surgery involved lateral incision, excision of the torn peroneus brevis segment, side-to-side anastomosis of the peroneal longus to brevis, peroneal tubercle planing, and lateral ankle ligament imbrication using anchors. The anastomosis was reinforced with TeKBrace synthetic graft. Postoperative protocol included non-weight-bearing in a posterior splint for 1 week, short leg cast for 2 weeks, and full weight-bearing in a walking boot at 3 weeks. Results The augmentation facilitated early mobilization and protected weightbearing, resulting in minimal muscle atrophy, shorter rehabilitation time, rapid return to activities, and no device-related complications (infection, foreign body reaction, or mechanical failure). Conclusion This single case highlights the feasible use of TeKBrace augmentation in peroneal longus to brevis transfer, suggesting potential benefits for select patients with complex peroneal tendon reconstructions. Larger series with longer-term outcomes are needed to confirm durability, integration, and any advantage over nonaugmented transfers or other reinforcement options.

Background: Tibial pilon fractures are complex injuries frequently associated with persistent functional impairment, even after successful surgical fixation. While previous studies have reported deficits in muscle strength and balance, little is known about the side-to-side variations in intrinsic biomechanical and viscoelastic muscle properties following surgery. Objectives: This study aimed to compare the biomechanical and viscoelastic properties of ankle periarticular muscles between the affected and non-affected limbs in patients with surgically treated unilateral tibial pilon fractures. A secondary objective was to evaluate the relationship between intrinsic muscle properties and isometric muscle force. Methods: A total of 39 subjects with unilateral surgically treated tibial pilon fractures were evaluated after fracture healing. Myotonometric assessment was performed to evaluate muscle mechanical parameters, including tone (frequency), stiffness, and elasticity (decrement), as well as viscoelastic properties, including relaxation time and creep, in the tibialis anterior, peroneus longus, medial gastrocnemius, and lateral gastrocnemius muscles. Isometric muscle force of ankle dorsiflexors and plantar flexors was measured using a handheld dynamometer. Side-to-side comparisons and Pearson correlation analyses were performed. Results: The affected limb showed significantly reduced ankle range of motion in all planes and significantly lower isometric muscle force in both the dorsiflexors (p = 0.0002) and the plantar flexors (p = 0.0066). Stiffness was significantly higher in the medial (p = 0.038) and lateral gastrocnemius (p = 0.045) muscles on the affected side. Decrement was significantly increased (indicating reduced elasticity) in the peroneus longus (p = 0.021). No significant differences were observed for tone, relaxation time, or creep. Conclusions: Myotonometry revealed increased stiffness in the gastrocnemius muscles and reduced elasticity in the peroneus longus on the operated side compared with the non-affected limb. Tone and viscoelastic properties did not differ significantly between sides. However, tone, stiffness, and elasticity were significantly correlated with muscle force, indicating a relationship between intrinsic muscle mechanical properties and force production after tibial pilon fracture surgery.

Background: Conditioning activity (CA) is used to elicit post-activation performance enhancement (PAPE), but it is unclear whether load response principles from back squat models generalize to unilateral split squat conditioning when external load and surface instability are manipulated together. Thus, the current study examined acute effects of stable vs. unstable split squat CA with or without external load on jump performance and phase-specific electromyography (EMG). Methods: Twenty men completed a randomized crossover of three CAs (2 × 3 reps): unloaded stable split squat (SS), unloaded BOSU SS, and BOSU loaded at 50% split squat one-repetition maximum. Single leg jump (SLJ) and countermovement jump (CMJ) were assessed pre-CA and at 3 min (SLJ) and 4 min (CMJ) post-CA. EMG was recorded from the biceps femoris (BF), semitendinosus (ST), vastus lateralis (VL), vastus medialis (VM) gluteus medius (Gmed), peroneus longus (PL), gastrocnemius lateralis (GL) and gastrocnemius medialis (GM). Signals were time-normalized across the split squat cycle and quantified using phase-specific area under the curve (AUC) (descending/ascending). Results: SLJ and CMJ increased after all conditions compared with the pre-test (p < 0.05). SS and unloaded BOSU SS produced comparable jump outcomes, whereas BOSU loaded yielded the greatest CMJ increase (p < 0.04). Unloaded BOSU SS selectively increased hamstring activation (BF, ST) without changes in Gmed or PL. BOSU loaded increased EMG amplitude across all measured muscles. Conclusions: External load primarily drives acute CMJ potentiation, whereas instability mainly redistributes recruitment toward the hamstrings without improving jump performance beyond the stable condition. These findings indicated that when the goal is acute jump enhancement, external load should be prioritized, whereas unstable surfaces may be used to selectively target posterior chain activation.