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Motion-Agent: A Conversational Framework for Human Motion Generation with LLMs
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Motion-Agent pairs GPT-4 as a conversational planner with MotionLLM, a LoRA-adapted Gemma2-2B that translates between text and discrete motion tokens, to support multi-turn motion generation, editing, and captioning.
Problem
3D human motion generation and understanding methods typically need extensive task-specific training, handle long complex prompts poorly, and lack multi-turn conversational control.
Approach
Motion is quantized into discrete tokens added to a pre-trained LLM's vocabulary; only LoRA adapters are trained on text-motion pairs, and a frozen GPT-4 decomposes user requests into multiple MotionLLM calls whose token outputs are concatenated and detokenized, enabling long and edited motions without extra training.
Key results
- MotionLLM reaches R-precision Top-1 0.515 and FID 0.230 on HumanML3D generation, competitive with trained-from-scratch models while fine-tuning only a small fraction of parameters.
- On HumanML3D captioning, MotionLLM reports BLEU@4 17.65, ROUGE 48.7, and BERTScore 42.63, above TM2T, MotionGPT, and MotionChain.
- MotionLLM reports the best Diversity (9.908) among the compared generation methods on HumanML3D.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use MotionLLM instead of MoMask for text-to-motion generation | MotionLLM · HumanML3D test set | Diversity: 9.620^{ \pm .064} -> 9.908^{ \pm .102} | Helped |
| Use MotionLLM instead of MoMask for text-to-motion generation | MotionLLM · HumanML3D test set | FID: 0.045^{ \pm .002} -> 0.230^{ \pm .009} | Hurt |
| Use MotionLLM instead of MoMask for text-to-motion generation | MotionLLM · HumanML3D test set | R Precision Top 1: 0.521^{ \pm .002} -> 0.515^{ \pm .004} | Hurt |
| Use MotionLLM instead of prior captioning models | MotionLLM · HumanML3D test set | Bleu@4: 12.56 -> 17.65 | Helped |
| Use MotionLLM instead of prior captioning models | MotionLLM · HumanML3D test set | Cider: 33.70 -> 33.74 | Helped |
| Increase LoRA rank from 16 to 64 (ablation) | MotionLLM with Gemma2-2b · KIT-ML | R Precision Top 1: 0.411 -> 0.422 | Helped |
| Increase LoRA rank from 16 to 64 (ablation) | MotionLLM with Gemma2-2b · KIT-ML | FID: 0.745 -> 0.658 | Helped |
| Increase LoRA rank from 16 to 64 (ablation) | MotionLLM with Gemma2-2b · KIT-ML | Multimodal Dist: 2.994 -> 2.929 | Helped |
| Increase LoRA rank from 16 to 64 (ablation) | MotionLLM with Gemma2-2b · KIT-ML | Diversity: 11.313 -> 11.195 | Hurt |
| Use Gemma2-9b instead of Gemma2-2b at LoRA rank 32 (ablation) | MotionLLM · KIT-ML | R Precision Top 1: 0.415 -> 0.439 | Helped |
| Use Gemma2-9b instead of Gemma2-2b at LoRA rank 32 (ablation) | MotionLLM · KIT-ML | FID: 0.712 -> 0.438 | Helped |
| Use Gemma2-9b instead of Gemma2-2b at LoRA rank 32 (ablation) | MotionLLM · KIT-ML | Diversity: 11.251 -> 11.151 | Hurt |
Surprising findings
- Smaller open LLMs (Llama-3-7B, Mixtral-8x7B) often failed to follow the required JSON format, so the agent could not parse their plans.
Limitations
- No 3D scene or environment interaction modeling, and no detailed hand or facial motion.
- Multi-human generation is only a preliminary trial and not fully explored.
- Long-motion and multi-turn results are qualitative, with no established ground truth or quantitative evaluation.
Experimental setup
Datasets: HumanML3D KIT-ML
Benchmarks: HumanML3D KIT-ML
Metrics: R-precision Top-1 R-precision Top-3 FID MultiModal Distance Diversity BLEU@1 BLEU@4 ROUGE CIDEr BERTScore
Baselines: T2M TM2T MDM MLD MotionDiffuse T2M-GPT MotionGPT MotionChain MoMask
Builds on: T2M-GPT MotionGPT LoRA VQ-VAE
Closest papers by meaning
- The Language of Motion: Unifying Verbal and Non-verbal Language of 3D Human Motion (CVPR 2025 · similarity 0.90)
- ReMoGPT: Part-Level Retrieval-Augmented Motion-Language Models (AAAI 2025 · similarity 0.88)
- MotionGPT: Finetuned LLMs Are General-Purpose Motion Generators (AAAI 2024 · similarity 0.88)
- Generating Human Motion in 3D Scenes from Text Descriptions (CVPR 2024 · similarity 0.88)
- AvatarGPT: All-in-One Framework for Motion Understanding Planning Generation and Beyond (CVPR 2024 · similarity 0.88)
- HSI-GPT: A General-Purpose Large Scene-Motion-Language Model for Human Scene Interaction (CVPR 2025 · similarity 0.87)
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