Matt Strong

Matt Strong

CS PhD at Stanford University

← Paper Digest

Enhancing Balance and Posture in Material Handling Tasks with a Wearable Robotic Tail

Eisa Anwar, Sajeeva Abeywardena, Stuart C. Miller, Ildar Farkhatdinov

November 2026

TL;DR A wearable robotic tail swings a 3 kg counterweight behind the user to offset a load held out in front. In a 10-person shelf-loading study it cut peak centre-of-pressure displacement by 17-20 mm and peak trunk inclination by 4.3 degrees compared with no tail.

What they do

Placing a load on a shelf in front of you pushes your centre of pressure (CoP) toward your toes and makes you lean forward. Instead of an exoskeleton, the authors test a supernumerary limb: a wearable tail that swings backwards to counterbalance the load. Ten participants aged 20-31 moved a 4 kg load onto and off a 135 cm platform 40 cm in front of their feet, with the tail active, worn but unpowered (passive), and not worn.

How it works

  • Hardware. The tail, from the authors’ earlier work, is a 3 kg counterweight that can extend 50 cm behind the user; the whole system weighs about 6 kg.
  • Load sensing. The load sits on a handheld platform with force sensors, tethered to the wearable frame by a pull-rope encoder and a rotary encoder that measure its distance from the body.
  • Control. A static model gives the CoP offset caused by the load; the tail angle that produces an equal and opposite offset is tracked by a PD controller on a Teensy 4.1, with under 60 ms latency.
  • Measurements. Force plate, motion capture of trunk and ankle, and EMG on erector spinae, gastrocnemius, tibialis anterior and biceps; 15 repetitions per condition in random order.

Results

  • Peak CoP displacement, active tail vs no tail: 17 mm (22%) lower in placement, 20 mm (22%) lower in retrieval. The passive tail did not differ from no tail.
  • Peak trunk inclination fell 4.3 degrees (47%) with the active tail and 2.4 degrees with the passive tail; ankle angles did not change.
  • Average erector spinae activity, active vs no tail: 9% lower in placement, 28% lower in retrieval. Peak gastrocnemius activity fell 36% in placement.
  • Integrated biceps activity rose 15% with the active vs passive tail during retrieval.

Limitations

An imitated shelving task in the lab, with ten non-professional participants and one 4 kg load. The prototype still needs to become more compact, portable and power-efficient. Movement duration was not measured, so the biceps increase is not explained.

Figures

From Figure 1: The custom-built wearable robotic tail worn by a user during the object handling task.
From Figure 1: The custom-built wearable robotic tail worn by a user during the object handling task.
From Figure 5: (A) The setup and sensors: motion tracking markers, EMG sensors and a force plate under the participan...
From Figure 5: (A) The setup and sensors: motion tracking markers, EMG sensors and a force plate under the participant. (B) The two tasks, load placement and load retrieval. (C) The three conditions: tail powered and active, tail unpowered and passive, and no tail.
From Figure 2: (A) Centre of pressure over time for one participant during placement and retrieval: active tail (blue...
From Figure 2: (A) Centre of pressure over time for one participant during placement and retrieval: active tail (blue), passive tail (green), no tail (orange) and static standing (yellow); grey lines mark the front and back of the feet. (B) Peak displacement and range of motion of the centre of pressure for all participants, one colour per participant, with the significant percentage changes.
Abstract

Frequent heavy lifting is linked to musculoskeletal strain, with lower back pain affecting up to 40% of manual labourers. Inspired by animals using tails for balance, we developed a wearable robotic tail as a dynamic counterbalance. Ten participants performed an imitated shelf loading/unloading task across three conditions: active tail, passive tail, and no tail. Kinematics, centre of pressure, and muscle activation (gastrocnemius, erector spinae, tibialis anterior, biceps brachii) were measured. Compared with no tail, the active tail achieved >20 mm reduction in centre of pressure peak displacement, 4.3 degree reduction in trunk motion, and >9% and >20% reductions in erector spinae and gastrocnemius activity, respectively. The passive tail produced smaller reductions, suggesting passive counterbalancing helps while active movement augments it further. Biceps brachii activation increased with the active versus passive tail. The ankle kinematics and tibialis anterior activation were unchanged. These findings support wearable robotic tails for improving balance during material handling.

Summaries are written automatically from each paper's text. Figures and videos come from the paper and its project page; all credit goes to the authors.